Chemistry Year 9 Textbook PDF

Chemistry Year 9 Textbook This textbook will be available in digital format (PDF) only. It is intended to be used by secondary school students and teachers in Malta and Gozo. It leads students to sit for the SEC06 Chemistry examination from 2025 onwards. Version history Version 1.0 distributed in January 2022. Version 1.1 distributed in August 2023. Contains updates related to changes made to the SEC06 Chemistry syllabus. Some areas have been rearranged and/or reworded to reflect feedback received from teachers. Acknowledgements Mizzi Doreen (HoD – Secretariat for Catholic Secretariat Education), Zammit Robert (HoD), Zarb Dennis (HoD), and Mercieca Michael (EO) edited this textbook. Azzopardi Orietta (Tr), Balzan Maria (Tr), Bezzina Josepha (Tr), Camilleri Rose Marie (Tr), Curmi Alexia (Tr), Cuschieri Cheryl Ann (Tr), Dalli Charmaine (Tr), Farrugia Sacco Carmen (Tr), Sant Rebecca Marie (Tr), Vassallo Sarah (Asst Head), Mizzi Doreen (HoD), and Mercieca Michael (EO) contributed towards subject content. Zammit Robert (HoD), Attard Elizabeth (Tr) with the help and support of Chircop Godwin, Debono Leandro, and Micallef Mario (Laboratory Technicians) contributed towards the provision of video clips that were shot at St. Ignatius Secondary School, Ħandaq, Qormi. Special thanks go to Zammit Robert for coordinating and editing these video clips. Gafa’ Louise (Tr), Grech Melanie (Tr), Scicluna Mantas Maria-Liza (Tr), and Mercieca Michael (EO) contributed towards snippets of information. Fsadni Geraldine (Tr) contributed towards sourcing animations. Abela Claire (Tr) contributed towards designing diagrams. Magro Miriana (Tr) contributed towards sourcing pictures. Mercieca Michael (EO) contributed towards the frontpage and typesetting. This e-book was reviewed by all chemistry teachers who attended CoPE sessions. Special thanks go to Dr Christine Firman (EO) and her team at SpLD (MYER) for their contribution towards making this textbook more user friendly as well as Audrey Vella Bondin (EO Physics) for her contribution to the section regarding the nature of science. i Chemistry Year 9 Textbook How to use this e-book This e-book is closely linked to the SEC Chemistry Learning Outcomes Framework syllabus which can be downloaded at: https://www.um.edu.mt/matsec/syllabi/secsyllabi2025 Each chapter represents the work expected in one learning outcome. Each chapter, except for chapter one, starts with a graphic that indicates the subject focus, which the learning outcome is part of. Chapters are split into sections that deal with groups of related assessment criteria. These assessment criteria are declared so that students can focus on what needs to be learned. Hyperlinks link to content that is online and serve to further develop students’ knowledge. Online content is not examinable however students are encouraged to follow these links to further their understanding of the role of chemistry in the real world. An internet connection is required to access video clips, animations, and online content. When using the digital version of this e-book, QR codes can be clicked to access the online resources. When using this e-book on a computer, use the navigation feature provided by your PDF viewer. Throughout this e-book you will find one of five types of textboxes shown below: This textbox shows exercises related to content that students can work on their own or with their teachers. This textbox shows snippets of information that are NOT meant to be studied for your examination, but which give extra information related to discoverers, discoveries, and further relevant content. This textbox shows a QR code which links to an online video clip. Click on the QR code when using the digital version to access the resource. This textbox shows a QR code which links to an animation. Click on the QR code when using the digital version to access the resource. This textbox shows a QR code which links to further reading. Click on the QR code when using the digital version to access the resource. Definitions and important information is presented on a blue background. ii Chemistry Year 9 Textbook Contents 1 UNDERSTANDING HOW CHEMISTRY WORKS AND IS COMMUNICATED (LO 1).................................................... 1 1.1 UNDERSTANDING THE SCIENTIFIC PROCESS.................................................................................................................... 1 1.1.1 The nature of scientific knowledge............................................................................................................. 1 1.2 HEALTH AND SAFETY................................................................................................................................................. 3 1.2.1 General rules............................................................................................................................................... 3 1.2.2 Glassware.................................................................................................................................................... 3 1.2.3 Fire.............................................................................................................................................................. 4 1.2.4 Electricity..................................................................................................................................................... 5 1.2.5 Fume cupboard........................................................................................................................................... 5 1.2.6 Chemical substances................................................................................................................................... 6 1.3 PERFORMING EXPERIMENTS....................................................................................................................................... 8 1.3.1 Laboratory apparatus................................................................................................................................. 8 1.4 REPORT WRITING................................................................................................................................................... 11 1.4.1 Aim of the experiment.............................................................................................................................. 17 1.4.2 Drawing and labelling diagrams............................................................................................................... 17 1.4.3 Identifying variables in an experiment...................................................................................................... 20 1.4.4 Precautions and safety considerations..................................................................................................... 23 1.4.5 Recording observations and measurements............................................................................................. 23 1.4.6 Plotting graphs.......................................................................................................................................... 24 1.4.7 Reading and interpreting graphs.............................................................................................................. 24 1.4.8 Sketching graphs....................................................................................................................................... 25 1.4.9 Discussing results and drawing conclusions.............................................................................................. 26 1.4.10 Evaluating a laboratory report................................................................................................................. 26 1.5 INVESTIGATIVE EXPERIMENTS................................................................................................................................... 27 2 GASES FOUND IN AIR AND THEIR LAB PREPARATION (LO 2)............................................................................. 30 2.1 GASES IN THE EARTH’S ATMOSPHERE......................................................................................................................... 30 2.1.1 Composition of air..................................................................................................................................... 30 2.1.2 Measuring the percentage of oxygen in air.............................................................................................. 31 2.1.3 Properties and uses of the gases in dry air............................................................................................... 33 2.2 ELEMENTS, COMPOUNDS, AND MIXTURES................................................................................................................... 36 2.2.1 Mixtures.................................................................................................................................................... 36 2.2.2 Elements.................................................................................................................................................... 37 2.2.3 Compounds............................................................................................................................................... 38 2.3 THE PERIODIC TABLE OF THE ELEMENTS..................................................................................................................... 39 2.3.1 Chemical naming and symbols.................................................................................................................. 41 2.4 THE NUCLEAR MODEL - PROTONS, NEUTRONS, AND ELECTRONS....................................................................................... 43 2.4.1 Atomic number and mass number............................................................................................................ 45 2.4.2 Electrons in shells...................................................................................................................................... 47 2.4.3 Relationship between electron structure, group, and period number...................................................... 49 2.4.4 Isotopes..................................................................................................................................................... 50 2.4.5 Relative atomic mass................................................................................................................................ 51 2.4.6 Monoatomic elements.............................................................................................................................. 53 2.4.7 Formation of molecules............................................................................................................................ 53 2.4.8 Valency...................................................................................................................................................... 54 2.5 COVALENT BONDING.............................................................................................................................................. 55 2.5.1 Covalent bonding between atoms of the same non-metals..................................................................... 56 2.5.2 Covalent bonding between atoms of different non-metals...................................................................... 58 iii Chemistry Year 9 Textbook 2.5.3 Chemical formulae of covalent compounds.............................................................................................. 60 2.5.4 Properties of covalent compounds............................................................................................................ 61 2.6 REPRESENTING CHEMICAL REACTIONS........................................................................................................................ 62 2.6.1 Word equations........................................................................................................................................ 62 2.6.2 States of matter........................................................................................................................................ 62 2.6.3 Balanced chemical equations.................................................................................................................... 63 2.7 DIFFUSION AND DENSITY OF GASES............................................................................................................................ 66 2.7.1 Diffusion.................................................................................................................................................... 66 2.7.2 Density of gases........................................................................................................................................ 68 2.8 PREPARING, COLLECTING, AND TESTING FOR GASES....................................................................................................... 69 2.8.1 Preparing gases......................................................................................................................................... 69 2.8.2 Collecting gases........................................................................................................................................ 70 2.8.3 Testing for gases....................................................................................................................................... 74 2.9 ATMOSPHERIC POLLUTION....................................................................................................................................... 75 2.9.1 Greenhouse gases..................................................................................................................................... 75 2.9.2 Carbon monoxide...................................................................................................................................... 79 2.9.3 Complete and incomplete combustion..................................................................................................... 80 2.9.4 Particulates............................................................................................................................................... 82 2.9.5 Sulfur dioxide............................................................................................................................................ 83 2.9.6 Nitrogen oxides (NOx)............................................................................................................................... 84 2.9.7 Acid rain.................................................................................................................................................... 86 2.9.8 Chlorofluorocarbons and ozone................................................................................................................ 87 3 THE SOLVENT ACTION OF WATER INCLUDING THE IMPACT OF WATER HARDNESS (LO 3)................................. 91 3.1 WATER – A SOURCE OF LIFE AND CONFLICT................................................................................................................. 91 3.2 POTABLE WATER SOURCES IN MALTA......................................................................................................................... 92 3.2.1 Ground water............................................................................................................................................ 93 3.2.2 Reverse osmosis........................................................................................................................................ 94 3.2.3 Desalination through distillation.............................................................................................................. 95 3.3 PROPERTIES OF PURE WATER.................................................................................................................................... 96 3.3.1 Hydrated salts........................................................................................................................................... 97 3.3.2 Testing for the presence of water............................................................................................................. 97 3.4 MIXTURES............................................................................................................................................................ 98 3.4.1 Mixed states.............................................................................................................................................. 98 3.4.2 Solid/liquid mixtures - Soluble substances................................................................................................ 98 3.5 OBTAINING TABLE SALT........................................................................................................................................... 99 3.5.1 Production of salt from seawater in Malta............................................................................................... 99 3.5.2 Production of salt from rock salt............................................................................................................. 100 3.5.3 Separation techniques............................................................................................................................ 101 3.6 SALTS AND IONIC BONDING.................................................................................................................................... 103 3.6.1 Ionic (electrovalent) bonding.................................................................................................................. 104 3.6.2 Valency.................................................................................................................................................... 105 3.6.3 Writing chemical formulae of ionic substances...................................................................................... 110 3.6.4 Balancing chemical equations - revisited................................................................................................ 115 3.7 SOLVENT ACTION OF WATER, SOLUTION, AND SOLUBILITY............................................................................................. 118 3.7.1 Dilute and concentrated solutions.......................................................................................................... 119 3.7.2 Solubility rules......................................................................................................................................... 119 3.7.3 Solubility of solids and gases in water.................................................................................................... 120 3.8 HARD AND SOFT WATER........................................................................................................................................ 123 3.8.1 Water hardness....................................................................................................................................... 123 3.8.2 Softening of hard water.......................................................................................................................... 124 3.8.3 Testing for water hardness..................................................................................................................... 127 iv Chemistry Year 9 Textbook 3.8.4 Advantages and disadvantages of hard water....................................................................................... 129 4 ACIDS, BASES, AND SALTS (LO 4)......................................................................................................................131 4.1 INDICATORS........................................................................................................................................................ 132 4.2 ACIDS................................................................................................................................................................ 134 4.2.1 Strong and weak acids............................................................................................................................ 134 4.2.2 Properties of acids................................................................................................................................... 135 4.3 BASES AND ALKALIS.............................................................................................................................................. 136 4.3.1 Strong and weak alkalis.......................................................................................................................... 137 4.3.2 Properties of alkalis................................................................................................................................. 137 4.4 METALLIC AND NON-METALLIC OXIDES..................................................................................................................... 138 4.4.1 Acidic and neutral oxides........................................................................................................................ 138 4.4.2 Basic and amphoteric oxides................................................................................................................... 139 4.5 ACID REACTIONS.................................................................................................................................................. 140 4.5.1 Reactions of acids with bases................................................................................................................. 140 4.5.2 Reactions of acids with metals................................................................................................................ 141 4.6 APPLICATIONS OF ACID-BASE CONCEPTS IN REAL-LIFE SITUATIONS.................................................................................. 143 4.6.1 Acid rain.................................................................................................................................................. 143 4.6.2 Neutralisation of acid soils...................................................................................................................... 144 4.6.3 Excess stomach acidity............................................................................................................................ 145 4.7 SALTS................................................................................................................................................................ 146 4.7.1 Making salts............................................................................................................................................ 147 4.7.2 Some useful salts..................................................................................................................................... 150 5 PERIODIC TABLES OF THE ELEMENTS................................................................................................................152 v Chemistry Year 9 Textbook 1 Understanding how chemistry works and is communicated (LO 1) 1.1 Understanding the scientific process By the end of this section, you should be able to: State that scientific knowledge changes with new evidence/ observations/ experiments. (1.1a) Distinguish between a fact, a hypothesis, and a theory. (1.2a) Discuss briefly the meaning of science in terms of its healthy scepticism, aimed objectivity, and the value of physical (observable/ measurable) evidence. (1.3a) 1.1.1 The nature of scientific knowledge People once thought that the Earth was flat. This was the dominant view before the 2nd century BC. From the evidence collected over the centuries this idea changed and we know that the Earth is a planet. Scientific knowledge is never absolute, it can change when new discoveries are made. So, one will wonder, what is science? How is scientific knowledge produced?1 Science consists of a body of knowledge and the process by which that knowledge is produced. We tend to think that science is a body of knowledge since we are presented with many different facts e.g., the Earth is round, electrons are negatively charged, etc. However, it is important to be aware how scientific knowledge is generated. This is known as the scientific process which is a way of building knowledge and making predictions about the world in such a way that they are testable. The question of whether Earth is flat or round, could be put to the test. This could be studied through multiple lines of research, and the evidence is evaluated to determine whether the evidence supports a round or flat planet. Different scientific disciplines typically use different methods and approaches to investigate the natural world, but objective testing lies at the core of scientific inquiry for all scientists. As scientists analyse and interpret their data, they generate hypotheses and theories which help explain their results and place them in context of the larger body of scientific knowledge. These different kinds of explanations are tested by scientists through additional experiments, observations, modelling, and theoretical studies. Thus, the body of scientific knowledge builds on previous ideas and is constantly growing. It is deliberately shared with colleagues through the process of peer review, where scientists comment on each other's work, and then through publication in the scientific literature, where it can be evaluated and integrated into the body of scientific knowledge by the larger community. Scientists’ beliefs, knowledge and experiences influence their observations and interpretations. Observations are never neutral but are always interpreted from within theoretical frameworks which introduce an element of subjectivity. Scientists attempt to be “open minded and apply mechanisms such as peer review and data triangulation to improve objectivity” (Chen, 2006, p. 806). One of the hallmarks of scientific knowledge is that it is subject to change, as new data are collected, and reinterpretations of existing data are made. Scientific knowledge, therefore, 1 Adapted from https://www.visionlearning.com/en/library/Process-of-Science/49/The-Nature-of-Scientific-Knowledge/185 1 Chemistry Year 9 Textbook although reliable, does not lead to absolute truth and is subject to change in the light of new evidence or interpretations or social and cultural changes. Changes can take place in two ways: evolutionary when theories evolve with new evidence or interpretations, revolutionary when theories are completely replaced by new theories following new evidence or interpretation. Major theories, which are supported by multiple lines of evidence are rarely completely changed, but new data and tested explanations add nuance and detail. Scientific knowledge helps people understand and answer questions about the world around us. Science is built on several facts conceived through several theories. Theories are generated through evidence, observation, and experimentation. This is the nature of scientific knowledge. If the theory supports the evidence collected through observation and experimentation, and is also able to make predictions, then facts and knowledge are retained. If not, new experiments have to be constructed. The observations and evidence collected through these new experiments may change the nature of scientific knowledge. For this reason, scientific knowledge is dynamic and is constantly developing. Generation of scientific knowledge also involves human creativity at all stages of investigations; prior to, during collection and interpretation of data, and during generation of conclusions. Scientists also use imagination together with logical reasoning to create scientific knowledge. Finally, science is a human endeavour which is affected by the culture and society it is accomplished in. Cultural values as well as power structures such as religion, political and economic factors, influence how science is conducted and interpreted. Such properties are exhibited through public funding for scientific research. The following table shows the differences between the terms: fact, hypothesis, and theory. Term Meaning Example A phenomenon that has been observed Mercury is the only metallic Fact to be true and has been repeatedly element that is liquid at standard confirmed to be so. temperature and pressure. A tentative explanation about an Soluble solids would dissolve faster Hypothesis observation. A hypothesis triggers off a if the temperature of the water is series of experiments/investigations. increased. An explanation of why a phenomenon Theory occurs, which has been substantially The Kinetic Theory of Matter confirmed by facts and hypotheses. Scientists continuously utilize critical thinking and reasoning skills in order to evaluate existing evidence. This is referred to as healthy scepticism. This dynamic, logical approach to science enhances the validity of scientific results and deepens understanding. Scientific knowledge is built through an accumulation of observations and experimentation. For this reason, it is healthy to adopt an objective approach in science. When planning and conducting experiments, gathering observable and measurable evidence, reporting observations and results, and communicating experimental outcomes; scientists need to do so within a frame of mind free from bias and personal interest. The scientific method. 2 Chemistry Year 9 Textbook 1.2 Health and safety By the end of this section, you should be able to: Follow health and safety regulations. (1.1e) State health and safety considerations. (1.2e) Evaluate an experiment in terms of health and safety. (1.3e) Studying chemistry involves a good amount of laboratory work where glassware, fire, electricity, and chemical substances are used. Always follow the instructions provided by your teacher while performing experiments in the laboratory. 1.2.1 General rules When you are in a chemistry laboratory, follow the rules below: Always wear eye protection. Always wear a laboratory coat. Wash your hands regularly. Keep your work area clear and tidy. Never eat or drink in the laboratory. Check the SDS (Safety Data Sheet also known as MSDS that is Material Safety Data Sheet) of chemicals before starting work and take the necessary precautions. Clean up all spillages immediately. Keep long hair tied back. Wear appropriate clothing that does not leave skin exposed (e.g. shorts, skirts, sandals). Label bottles and other containers clearly and correctly. Do not write directly on to bottles where the ink can run or be easily removed, e.g. by solvent. Keep walkways clear. Check glassware for damage, cracks, and broken edges before use. Make sure all equipment is in good working order and fit for use. (List adapted from: rsc.org) 1.2.2 Glassware Glassware refers to any equipment that is used in the laboratory which is made of glass. Laboratory equipment is made of glass as it is transparent, resists heating and easy to clean. However, glass is brittle and can break if not handled properly. The problem with glass is that as it breaks, it forms sharp edges that can penetrate one’s skin causing serious injury. In the event that glassware is broken, do NOT handle the broken pieces bare handed. Inform your teacher that glassware has been broken. Your teacher will take note of the equipment broken, wear protective gloves to handle the larger pieces and then use a brush and dustpan to remove the smaller pieces. The broken glassware will then be placed in a container marked accordingly to prevent injury to other people. 3 Chemistry Year 9 Textbook 1.2.3 Fire On some occasions, chemical reactions need to be heated so that a chemical reaction can proceed at a desired rate. In a chemistry laboratory this is often done using a Bunsen burner. Since a Bunsen burner produces a naked flame, it is important to handle this equipment with care. Wear eye protection. People with long hair must pull it up to prevent their hair from catching fire. Avoid leaning over the bench while working especially if a Bunsen burner is in use! collar air hole gas inlet (LPG) The Bunsen burner is designed such that it has a collar that one can rotate to control the amount of air that is mixed with the LPG by controlling the size of the air hole. This is a safety feature that is inbuilt so that when the burner is not in use the air hole is closed to produce a yellow flame, which is more visible than a clean blue flame. When the air hole is opened, a blue Bunsen burner flame is produced that must be used while heating since it produces the hottest flame and does not produce soot, which makes glassware black. Some chemical substances are said to be flammable or inflammable. These two words both mean that a substance can catch fire easily. Examples include ethanol (present in alcoholic beverages such as vodka) and propanone (also known as acetone and present in nail polish remover). Flammable substances should never be heated with a Bunsen burner flame as they will catch fire. These substances are marked with a flammable sign to inform the user of its fire risk. However, they can be heated either using a heating mantle or using a water bath. Heating mantle Water bath How to use the Bunsen burner. 4 Chemistry Year 9 Textbook 1.2.4 Electricity There will be instances when the use of electricity to perform experiments will be required. Electricity comes in two forms, either alternating current (AC) or direct current (DC). The electricity supply in the laboratory and at your home is supplied via three pin sockets which is of the AC type. It provides considerable power which is why it needs to be used with care. Usually, the type of electricity that is used by students in the laboratory is of the DC type which is provided by a special transformer that is connected to the AC laboratory power supply to provide a maximum of 20 V (Volt) DC. The red socket is the positive outlet while the black socket is the negative outlet. These power supplies provide safe DC power. However, caution must be always taken. 1.2.5 Fume cupboard A fume cupboard such as the one on the right, is an enclosed chamber that is open from one side only. It has a powerful pump that sucks air from the fume cupboard and passes it through a special filter to remove any toxic gases. Fume cupboards are used widely in laboratories and are designed to capture and remove air-borne hazardous substances generated during laboratory experiments (e.g., gases, vapours, aerosols, and particulates/dust). Experiments that involve toxic reactants and/or products are carried out in the fume cupboard. 1. State why the following laboratory rules need to be followed: a. Always wear eye protection. b. Always wear a laboratory coat. c. Never eat or drink in the laboratory. d. Keep long hair tied back. e. Wear appropriate clothing that does not leave skin exposed (e.g. shorts, skirts, sandals). 2. State the position that the collar of a Bunsen burner must be in to produce a blue flame. 3. Give an alternative name for the yellow flame produced by a Bunsen burner. Explain why the flame turns yellow when the Bunsen burner collar is closed. 4. Name the two types of electricity that are available. Which of them is used during science experiments in the lab? 5 Chemistry Year 9 Textbook 1.2.6 Chemical substances Some chemical substances are inert, while others have properties that might cause harm if inhaled, swallowed, or allowed to touch one’s skin. This does not mean that as junior chemists you should avoid using these substances. Being informed of their potential hazardous properties puts one in a better position to take the necessary precautions to perform experiments safely. For this reason, an international system of signs is in place to provide information of the hazards chemical substances might carry. You will find these symbols on the original packaging of materials and on laboratory reagent bottles. The table below shows the new and old hazard symbols. Hazard New Symbol Old symbol Corrosive Acute toxicity Serious health hazard Health hazard Flammable Oxidising Explosive Gas under pressure No symbol available. Hazard to the environment 6 Chemistry Year 9 Textbook All chemical substances have a Safety Data Sheet (SDS). This document can easily be accessed online by typing the name of the substance followed by SDS. SDS documents provide all the information required by chemists so they are informed of the hazard chemicals may pose. Knowing about the hazards in advance, makes working with chemicals that much safer as one would know how to handle these chemicals safely. All SDS documents have the same sixteen section format so that chemists all over the world know what to expect when reading these documents. All chemistry labs are required to have an easily accessible folder containing SDSs for all chemicals that are used in that laboratory. Meanwhile, your teacher will provide you with a simplified, student friendly version of these SDSs that you can use during your laboratory work. Below is an excerpt of one of these SDSs. 1. Give the name of the following hazard symbols: 2. Use the SDS for the following chemicals to complete the table below. Chemical Hazard Safety precaution Magnesium ribbon Hydrochloric acid (1.0 mol dm-3) Copper(II) sulfate crystals Crash Course Chemistry: Lab Techniques and Safety 7 Chemistry Year 9 Textbook 1.3 Performing experiments By the end of this section, you should be able to: Carry out, with supervision/ with limited supervision/ with no direct supervision, a written procedure for an experiment. (1.1h, 1.2h, 1.3h) To carry out experiments safely and accurately, the instructions given in your experiment task sheet must be read and followed carefully. Failing to do so could result in your experiment not working properly or even worse, causing injury to you and others. 1.3.1 Laboratory apparatus The first step towards performing experiments safely is to be familiar with the equipment being used. Knowing their names and what they are used for, is a must. This will allow you to follow the instructions in your experiment without misinterpretation. The table below shows the names and pictures of equipment that are commonly used during experiments. The table also includes how the equipment should be drawn in your diagrams, as well as what it is used for. Name Used for… Picture Diagram A test tube is used to mix chemical substances on a Test tube / boiling small scale while a tube boiling tube is used to heat substances to perform chemical reactions. Test tube rack Holding test tubes. Holding a test tube while it is being Not usually shown in Test tube holder heated on a flame to diagrams avoid burning yourself. Not usually shown in Test tube cleaner Cleaning test tubes. diagrams Measuring a specific Measuring cylinder volume of liquid. 8 Chemistry Year 9 Textbook Name Used for… Picture Diagram Pouring a liquid from one container into Glass funnel another to avoid spillage or used during filtration. Moving solid substances from their Not usually shown in Spatula container to a test diagrams tube, beaker, or flask. Holding and/or Beaker heating liquid substances. Holding and reacting liquid substances at room temperature. It is ideal for swirling Conical flask its contents as it avoids spilling. DO NOT HEAT AS IT MAY CRACK. Heating liquids/ Round bottomed powder on a Bunsen flask flame. Holding and reacting liquid substances at Flat bottomed flask room temperature. DO NOT HEAT AS IT MAY CRACK. Heating containers. It includes a safety feature to produce a or Bunsen burner safety flame. It can be represented by the following symbol: 9 Chemistry Year 9 Textbook Name Used for… Picture Diagram Holding a container above a heat source such as a Bunsen Tripod burner. DO NOT TOUCH WHEN HOT! Handling hot objects such as crucibles as Not usually shown in Crucible tongs well as wire gauzes diagrams etc. Placed between a container and a tripod. It helps to Wire gauze distribute heat ________________ evenly. DO NOT TOUCH WHEN HOT! Stirring substances Glass rod normally in a beaker. Holding a solid substance Watch glass temporarily. It is not meant to be heated. Heating solutions of Evaporating salts in a process dish/basin called evaporation to dryness. Heating solid substances to very Crucible with lid high temperature. DO NOT TOUCH WHEN HOT! Holding a crucible on a tripod. Pipe clay triangle DO NOT TOUCH WHEN HOT! Transferring a liquid into a reaction vessel. It must be Thistle funnel fitted such that its leg is underneath the level of the reacting liquid. 10 Chemistry Year 9 Textbook Name Used for… Picture Diagram Transferring a liquid into a reaction vessel Dropping funnel and allowing control over the amount added. Separating / tap Separating funnel immiscible liquids. Holding equipment at Stand and clamp a height and angle as required. Measuring Thermometer temperature. 1.4 Report writing By the end of this section, you should be able to: Structure a laboratory report in sections (1.2t). Write a scientific report for an experiment carried out (1.3t). Practical work is important in Chemistry. Through experiments you will develop experimental skills and techniques such as handling apparatus, performing tests or procedures, identifying variables to alter or control, conducting observations and measurements, and tabulating data. Furthermore, during data processing you can plot graphs, work out calculations, look for patterns and trends, analyse and interpret data observed, draw conclusions and link to scientific knowledge, principles, and theory. Conducting experiments will help you to get a feel of the phenomena such as they can make the connections between observing concrete evidence and the more abstract ideas or theories. The following template, published by SEC, shows the sections and respective notes that should be included in an experiment report. Third person past tense should be used in a report. 11 Chemistry Year 9 Textbook Write up of an experiment Date Write the date when the experiment was carried out in the lab. The title indicates the links to particular assessment criteria as outlined in Title the curriculum. Aim The purpose of the experiment is clearly stated. Apparatus A list of apparatus and materials/chemicals used during the experiment. Clear diagram/s of the experimental setup are to be drawn and labelled in Diagram pencil. Diagrams should not be too small nor too large. Procedure This section will be given to the students. A variables grid should be included specifying the independent variable (the Variables one which is changed during the experiment) and the dependent variable (the one which is measured for a change in the independent variable). (if applicable) Other variables which are kept constant, to ensure fair testing, should be included. A list of precautions taken to improve the accuracy of the experiment. Each Precautions precaution needs to be supported with reason/s explaining why such precautions are taken. Safety A short paragraph/list that identifies safety considerations associated with Considerations the preparation and implementation of the experiments to prevent any (if applicable) accidents Depending on the nature and type of the experiment: Observations can be written in paragraphs or in tables. Observations are to be written in a sequential order as noted during the different stages of the experiment. Results and Numerical results should be tabulated. Observations o Write the name of the measurement and its units in the column headers of the table of results. o Repeated readings should be taken when possible and recorded in the table. o Numerical values should be given to the same number of significant figures appropriate to the measuring device. Graphs are a pictorial way of looking at a table of results. Patterns can be observed, and anomalous results can be identified. Line graphs should include at least 5 data points. Processing Suitable scales should be chosen which makes it easy to plot data. data At least 2⁄3 of the graph paper should be used. Each axis should be labelled with the name and unit of the quantity being plotted. The data points should be clearly marked, and the points are joined to have a line of best fit or a smooth curve. 12 Chemistry Year 9 Textbook The line must go through the origin for quantities which are directly proportional. Data can also be presented in the form of bar graphs. Gradient of line graphs are calculated, and answers are given with the appropriate units. Show all steps in the calculations. In working calculations, the answer should have the same number of significant figures as the measurements used in the calculation. Avoid excessive rounding especially in calculations involving moles. Include the following points as applicable to the nature of the experiment. A summary of the findings of the experiments and relate them clearly to the aim of the experiment. A discussion of any patterns or trends in the data. State any relationships discovered or confirmed between variables Discussion being tested in the experiment. and Compare numerical results with known values from data books and Conclusion suggest any reasons for any differences. A complete analysis or interpretation of observations noted in the experiment (including balanced chemical equations and ionic equations where appropriate). Draw a conclusion based on experimental evidence and relate it to scientific knowledge, laws, and theory. Identify and comment on any sources of error in the experiment. Discuss any difficulties encountered in carrying out the experiment and Evaluation any precautions taken to achieve accuracy. Suggest way/s of improving the experimental set-up and or results. Suggest any other experiments which can be done to support the conclusions. Source: https://www.um.edu.mt/__data/assets/pdf_file/0007/509191/SEC062025Resources.pdf The following sample experiment report shows how a report should be written. SAMPLE EXPERIMENT REPORT Date: Write the date when the experiment was carried out. Title: The effect of surface area on the rate of a reaction. Aim: To determine the effect of changing surface area on the rate of a chemical reaction. Apparatus and materials: Measuring cylinder, conical flask, electronic balance, weighing boat, stopwatch, glass wool, pestle and mortar, calcium carbonate, dilute hydrochloric acid. 13 Chemistry Year 9 Textbook SAMPLE EXPERIMENT REPORT - Continued Procedure: 1. Measure 50 cm3 of dilute hydrochloric acid using a measuring cylinder. 2. Measure 1 g of crushed calcium carbonate and place in conical flask. 3. Pour the dilute acid in the conical flask and quickly close with a glass wool. 4. Switch on the stopwatch and measure the mass of flask and its contents at 1-minute intervals for 10 minutes. 5. Repeat the above steps using 1 g of larger lumps of calcium carbonate. Diagram: Variables: Independent variable Surface area of calcium carbonate Dependent variable Rate of loss of CO2 Controlled variables Mass of calcium carbonate, volume and concentration of acid, Temperature Precautions: Volume of acid in the measuring cylinder was read at eye level to prevent parallax errors. The following variables: volume and concentration of acid, mass of calcium carbonate, and temperature, were kept constant for fair testing. A glass wool was used to allow carbon dioxide to escape but prevents the acid spray from escaping. Safety considerations: Chemical Hazard Safety precautions hydrochloric acid Not hazardous Dilute acid may still cause harm to the eyes 1.0 mol dm -3 or the skin. Wear eye protection and use low volume and concentration. calcium carbonate Not hazardous Wear eye protection and avoid raising dust. Results and observations: When crushed calcium carbonate reacted with an acid faster effervescence took place. On the other hand, when larger pieces of calcium carbonate were added to the acid, slower effervescence was noted. In both experiments effervescence was fastest at the beginning. With time the rate of effervescence decreased in both reactions. 14 Chemistry Year 9 Textbook SAMPLE EXPERIMENT REPORT – Continued Mass of container Mass of container Time Mass of carbon Mass of carbon with large pieces of with small pieces of (min) dioxide (g) dioxide (g) Ca CO3 (g) Ca CO3 (g) 0 55.25 0 55.24 0 1 55.19 0.06 54.07 0.17 2 55.10 0.15 54.89 0.35 3 55.00 0.25 54.76 0.48 4 54.92 0.33 54.67 0.57 5 54.84 0.41 54.61 0.63 6 54.77 0.48 54.56 0.68 7 54.72 0.53 54.52 0.72 8 54.68 0.57 54.49 0.75 9 54.63 0.62 54.48 0.76 10 54.60 0.65 54.46 0.78 Processing data: Discussion and Conclusion: During this experiment calcium carbonate reacted with dilute hydrochloric acid to form calcium chloride, water and carbon dioxide as seen in the following equation: calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g) When calcium carbonate reacted with an acid, effervescence was observed since carbon dioxide gas was released. The gas escaped through the glass wool and the flask, and its contents became lighter. The rate of this reaction was followed by measuring the loss of carbon dioxide at regular time intervals for 10 minutes. 15 Chemistry Year 9 Textbook SAMPLE EXPERIMENT REPORT – Continued The aim of this experiment was to determine whether the surface area of a solid reagent affects the rate of a reaction. From the graph it can be concluded that the reaction of crushed calcium carbonate with acid was faster than the reaction of large calcium carbonate due to a steeper gradient. This experiment showed that by increasing the surface area of calcium carbonate the rate of reaction increased. From the graph it can also be concluded that initially in the first two minutes both reactions were fast. Then from the 3rd and 9th minute both reactions slowed down. On reaching the 10th minute both reactions were almost over since the effervescence slowed down considerably. This change in rate of reaction can be explained using the collision theory. Initially there are many successful collisions between the reactants resulting in a fast reaction. As the reagents are used up there are less successful collisions, hence the rate of reaction slows down. Moreover, by increasing the surface area of the solid reagent there are more exposed particles reacting with acid, leading to more successful collisions producing a faster reaction with crushed calcium carbonate. When larger pieces of calcium carbonate are used, the acid hits the outer layer of the calcium carbonate resulting in a slower reaction. Evaluation: The experiment produced a good set of readings to determine whether surface area affects the rate of reaction. However, the experiment could be improved by modifying the setup as shown in Figure 1. The calcium carbonate is placed in a small crucible in the conical flask filled with acid. The advantage of using this setup is that the reagents are quickly mixed, and the stopwatch can be started immediately. Secondly the experiment could run for a longer period of time such that the last three readings remain unchanged showing that the reaction is over. This experiment could also be carried out by collecting the gas in a gas syringe and noting the volume of gas at regular time intervals as shown in Figure 2. Figure 1 Figure 2 Besides changing the surface area, the rate of reaction of calcium carbonate and acid can be altered by changing the concentration of the acid, or by changing the temperature at which the reaction takes place. 16 Chemistry Year 9 Textbook 1.4.1 Aim of the experiment By the end of this section, you should be able to: State the aim/s of an experiment / investigation. (1.1d) The aim of the experiment is stated at the beginning of the lab report. It should be concise and indicates what you are about to do in the experiment. 1.4.2 Drawing and labelling diagrams By the end of this section, you should be able to: Label given diagrams (1.1k) Draw labelled diagrams from given apparatus (1.2k). Draw labelled diagrams of apparatus used during experiment/ investigations (1.3k) Diagrams are an important aspect of the laboratory report since they give a pictorial representation of the setup used during the experiment / investigation. If the experiment involves several separate setups, then a diagram for each setup is expected. Section 1.3.1 shows how laboratory apparatus is to be drawn in the report. A science stencil is useful to draw neat diagrams of the appropriate size. Follow the rules below when drawing and labelling diagrams: 1. Use a sharp pencil for the diagrams and labelling. Do not use a pen, coloured pencil, or blunt pencil. 2. Draw objects in two dimensions. Do not draw in 3D. 17 Chemistry Year 9 Textbook 3. Draw clean single lines. Do not draw sketchy lines. 4. Do not close off openings of glassware. 5. Use a ruler to draw straight lines. Do not draw lines freehand. 6. Do not shade or colour in. They might look nicer coloured in, but scientific diagrams need to be clear and simple. 18 Chemistry Year 9 Textbook 7. Do not float objects. If objects are in contact with each other, show it in the diagram. 8. Label objects with straight lines. Do not use arrow heads. Avoid crossing over lines. Write labels in a horizontal manner. (Rules and diagrams in this section adapted from: https://www.goodscience.com.au/year-7-chemistry/scientific-diagrams/) Lines with arrowheads should only be used to show movement such as the flow of a liquid. The size of a diagram must neither be too small nor too large. As a rule of thumb, the height of a diagram should not exceed 8 to 10 cm. 19 Chemistry Year 9 Textbook 1.4.3 Identifying variables in an experiment By the end of this section, you should be able to: Identify variables in an experiment (1.1c) Identify dependent, independent, and controlled variables. (1.3c) Some experiments are carried out to determine a cause-and-effect relationship. For example, does watering a plant (cause), improve growth (effect)? Source: https://theory.labster.com/experimental_variables/ There are many factors that could be altered, and these are known as variables. A variable is any factor, trait, or condition that can exist in differing amounts or types. An experiment usually has 3 types of variables: independent, dependent, and controlled. The independent variable is the factor whose values are changed and controlled by the scientist to study the cause and effect this has on the values of the dependent variable. In other words, it is the quantity the scientist is changing. To ensure a fair test, a good experiment has only one independent variable. The dependent variable is the factor that is being investigated in an experiment and it changes in response to the value of the independent variable. In other words, it is the quantity being measured after the independent variable is changed. The controlled variables are conditions which must be controlled and kept constant throughout the experiment so that they do not interfere with the dependent variable. When the experiment is repeated, the controlled variables must be the same. In the above experiment the variables will be as follows: Independent variable Volume of water. (the variable that is changed) Dependent variable Length/growth of plant. (the variable that is measured) Type of soil, intensity of light, Controlled variables same kind of plant, ambient (the variables that are kept the same) temperature, etc. 20 Chemistry Year 9 Textbook 1.4.3.1 Fair and objective testing in science By the end of this section, you should be able to: State the importance of fair (objective) testing in science. (1.1b) Discuss the importance of fair (objective) testing in science. (1.2b) Evaluate an experiment in terms of its objectivity. (1.3b) While performing science experiments, it is important to experiment fairly. This is done by changing only one factor (variable) at a time while all other conditions are kept constant (the same). The outcome of this variable on the experiment is observed and noted. Experimenting fairly helps increase the validity and reliability of the results obtained. For example, consider the following experiment: Experiment: To determine whether pure and salty water would take the same time to boil. One should note that there are several aspects shown in the setup that render this experiment useless since the experiments are not being done fairly. These aspects include: the volume of liquid used is not the same, and the number of candles used is not the same. When evaluating and applying experimental results, one needs to be aware of how objective the scientist was when planning, conducting, and reporting the experiment. Being objective implies that throughout the scientific process: the scientist was free from all bias, interest, and manipulations, the scientist considered all possible viewpoints when conducting the experiment, the experimental conclusions are an honest reflection of truthful facts that actually resulted from the experiment. 21 Chemistry Year 9 Textbook 1. Consider the following 2 experiments: Exp 1: Measuring the volume of oxygen gas in 3 minutes from hydrogen peroxide solution after addition of LARGE potato pieces with a total mass of 5 g. Exp 2: Measuring the volume of oxygen gas in 3 minutes from hydrogen peroxide solution after addition of SMALL potato pieces with a total mass of 5 g. a. Identify the dependent and independent variables. b. Identify the controlled variables to have a fair test. 2. Identify the variable being controlled in the following pairs of experiments. Examples of Paired Experiments Controlled Variable 1. Reaction between 2 g magnesium ribbon and 20 ml dilute hydrochloric acid. Reaction between 4 g magnesium ribbon and 20 ml dilute hydrochloric acid. 2. Reaction between 2 g magnesium ribbon and 20 ml dilute hydrochloric acid. Reaction between 2 g magnesium powder and 20 ml dilute hydrochloric acid. 3. Reaction between 2 g magnesium powder and 20 ml dilute hydrochloric acid. Reaction between 2 g magnesium powder and 20 ml concentrated hydrochloric acid. 3. Identify the independent and dependent variables in the following experiments. Experiment Independent Variable Dependent Variable Investigating the rate of production of oxygen gas when using hydrogen peroxide solutions of different concentrations. Investigating the rate of production of carbon dioxide gas when reacting dilute hydrochloric acid with powdered and lumpy calcium carbonate. Investigating the rise in temperature when reacting magnesium powder with dilute and concentrated hydrochloric acid. Investigating the mass of silver produced when exposing silver chloride to lights of various intensities. Investigating the effect on rhythm of the heart produced by varying potassium levels in the blood. 22 Chemistry Year 9 Textbook 1.4.4 Precautions and safety considerations By the end of this section, you should be able to: Identify precautions for a given experiment/ investigation (1.2f). Justify precautions for a given experiment/ investigation (1.3f). Before carrying out an experiment, the procedure must be read and understood. If there are steps that you do not understand, make sure to ask your teacher to clarify your misunderstanding. After reading the procedure, outline the precautions that need to be taken to improve the accuracy and reliability of the experiment. You also need to explain why each precaution needs to be taken. In a report, precautions are written in the third person past tense. Prior to an experiment, consult SDS documents for chemicals so that health and safety considerations are given due importance. Safety precautions related to glassware, electricity and fire should also be considered. Remember, that no matter how excited you may be to start your experiment; safety comes first for your sake and that of others. 1.4.5 Recording observations and measurements By the end of this section, you should be able to: Complete observations/ measurements in a given table for an experiment. (1.1i) Record all observations/ measurements in a given table for an experiment. (1.2i) Record observations/ measurements appropriately for an experiment/investigation. (1.3i, 1.2j) Determine which observations/ measurements are to be measured for an investigation. (1.3j) A written procedure will surely provide instances where you will need to measure quantities. Usually, a table is used to write and present the information that is measured during an experiment in an orderly manner. The first row would include the headings of the quantities that are being measured as well as calculated quantities where applicable. These headings also include the unit of measurement in brackets to avoid writing the unit of measurement with every measurement taken. It is important to write readings with the same number of decimal places. The independent variable usually goes into the first column and the dependent variable goes into the second column. At times you may decide to repeat the experiment to obtain more reliable data. The table of results would look like this. Dependent variable (unit) Independent variable (unit) Mean 1st trail 2nd trial 3rd trial (average) Apart from the measurement of quantities one needs to keep a watchful eye to what is happening during an experiment such as changes in state, colour, texture, odours, liberation of a gas (effervescence), emission or absorption of heat, etc. Any of these observable changes must be noted and included in your laboratory report. 23 Chemistry Year 9 Textbook 1.4.6 Plotting graphs By the end of this section, you should be able to: Plot a single series of data on given axes (1.1m). Plot a single series of data (1.2m). Plot multiple series of data on the same axes (1.3m). Not examinable in Year 9 During an experiment that involves measuring quantities, the information obtained is usually presented in a table. To better understand the relationship between variables, a graph would need to be plotted to obtain a visual perspective of the data obtained during the experiment. Plotting a graph involves some skills that need to be mastered as listed below: 1. Draw the x and y axes on your graph paper. 2. Label each axis with the variable it represents, including the units. 3. Put the independent variable on the x-axis and the dependent variable on the y-axis. 4. Identify the range of data you must include for each variable such that the graph would occupy at least 2⁄3 of the graph area. 5. Decide how many units every line on the graph represents for each of your variables. 6. Plot your data by using a plus (+) notation. Do not use an “×” to plot points. 7. Connect the data points with a best straight line or smooth curve depending on the general shape of the graph plotted. 8. Steps 5 and 6 should be repeated when plotting several series of data on the same graph. Use different symbols for the data points of each graph. Label each graph accordingly. 9. Write the graph’s title at the top of the graph. (List adapted from: https://www.wikihow.com/Make-a-Line-Graph) 1.4.7 Reading and interpreting graphs By the end of this section, you should be able to: Read values from simple graphical representations (1.1l). Interpret graphical representations containing single series of data (1.2l). Interpret multiple series of data plotted on the same axis (1.3l). Reading and interpreting graphs are two different skills that one needs to develop while studying Chemistry. Consider the solubility curves shown on the next page which show the solubilities of copper(II) chloride and sodium chloride at different temperatures. Reading a graph means that you should be able to give the values for the x and y axes of a given point on a graph. For example, at 44 °C, 40 g of sodium chloride dissolve in 100 g of water whereas at the same temperature, 34 g of copper(II) chloride dissolve in 100 g of water. At 56 °C both salts have the same solubility that is 42 g in 100 g of water. 24 Chemistry Year 9 Textbook Interpreting a graph means that when you look at the plotted graph, you should be able to tell how solubility varies with temperature. For example, the solubility of sodium chloride increases steadily with increasing temperature, but the solubility of copper(II) chloride rapidly increases with higher temperature. 1.4.8 Sketching graphs By the end of this section, you should be able to: Interpret situations by sketching a graph (1.2n) Interpret situations by sketching graphs in relation to existing plotted graphs (1.3n) Not examinable in Year 9 Sketching graphs means that you should be able to draw a graph without having specific coordinates. However, since you would know in advance what the graph should look like, you would be able to sketch the graph. The graph shown here shows a sketch of ice being heated until it melts and reaches room temperature. Note how the sketch shows the rise in temperature of the ice until it reaches the melting point, which is shown by the horizontal line and then the rise in temperature of the water is shown by the second slope. Sketches may also be drawn on existing plotted graphs to show how the plotted graph would change if a variable were changed in a particular way. 25 Chemistry Year 9 Textbook 1.4.9 Discussing results and drawing conclusion s By the end of this section, you should be able to: Draw conclusions from an experiment (1.2o) Draw conclusions from an experiment by relating it to scientific knowledge, laws, and theory (1.3o) After performing an experiment and processing data, you should be able to conclude your experiment by: Writing a summary of the findings of the experiments and relating them clearly to the aim of the experiment. Writing a discussion of any patterns or trends in the data. Stating any relationships discovered or confirmed between variables being tested in the experiment. Comparing numerical results with known values from data books and suggesting any reasons for any differences. Making a complete analysis or interpretation of observations noted in the experiment (including balanced chemical equations and ionic equations where appropriate). Drawing a conclusion based on experimental evidence and relating it to scientific knowledge, laws, and theory. 1.4.10 Evaluating a laboratory report By the end of this section, you should be able to: Identify sources of error to suggest improvements (1.2p) Evaluate an experimental procedure and results by suggesting improvements (1.3p). Your report should end with an evaluation where you should be able to: Identify and comment on any sources of error in the experiment. Discuss any anomalous results and try to explain why they happened. Discuss any difficulties encountered in carrying out the experiment and any precautions taken to achieve accuracy. Suggest way/s of improving the experimental setup and/or results. Suggest any other experiments which can be done to support the conclusions. 26 Chemistry Year 9 Textbook 1.5 Investigative experiments By the end of this section, you should be able to: Predict what might happen in an experiment/ investigation. (1.2g) Justify prediction/s made for an experiment/ investigation. (1.3g) Plan an experiment to solve a given problem with supervision. (1.2q) Plan an experiment to solve a given problem without direct supervision. (1.3q) Carry out an experiment to solve a given problem with supervision. (1.2r) Carry out an experiment to solve a given problem without direct supervision. (1.3r) An investigative experiment differs from a normal experiment in that you would be given a problem that needs to be solved. You will need to think of a solution and design an experiment to test your solution. Your plan (investigation outline) needs to be presented to your teacher so that s/he could assess your plan for health and safety issues only. When the plan is approved by your teacher, you will then execute your plan and perform the experiment that you proposed. Sometimes, when your plan may not be adequate, you will need to adjust it accordingly while you are performing the experiment. These changes need to be noted in the experimental procedure as well as in the evaluation section. The following template, as published by SEC, show the sections and respective notes that should be included in an investigation report. Write up of an investigation This section should contain an outline of the procedure that will be devised in the investigation together with scientific theory required to understand the investigation. The plan should be concise and written in the future tense. This section should include: The title. A short statement of the problem to be investigated. The aim of the investigation. A brief description of the scientific procedure. Investigation A list of materials and apparatus. outline Any pre-experiment work. A variables grid may be presented to highlight all the variables in the investigation (where applicable). Variables should be identified as independent and dependent variables. Other significant/relevant variables should be noted including the way they are controlled for results to be more reliable. Any background theory/research where applicable is given. The hypothesis section (where applicable) should give an outline of what may happen and why. (Note: Students are to be made aware that no marks will be lost if the hypothesis is disproved.) This section should include: Precautions Any precautions taken to achieve a more accurate result and improve and safety the outcome of the investigation. considerations Safety considerations associated with the preparation and implementation of the investigation to prevent any accidents. 27 Chemistry Year 9 Textbook This section should include: A detailed account of the procedure followed. All the steps involved to perform the experiment including any modifications made to the plan and any additional materials and apparatus used should be stated. The method should include measurements used, diagrams, and photos, where applicable. Procedure Note: Followed Results should not be included in this section. Third person past tense should be used. Any concentrations, measurements, amounts, times, and temperatures should be quantified. The procedure should be written in such a way that an independent person could repeat the experiment without referring to the person writing the report. This section should include: All observations and/or measurements should be presented in an organised form. Any calculated data should be presented showing all steps. Graphical representations should be used to display data when possible. Results and Note: observations Tables may be the best way of presenting data. Tables should have headings and units. An adequate number of readings should be taken especially if a graph has to be plotted. Results should not be interpreted in this section. Third person past tense should be used to describe any observations. This section should include: A brief summary of the aim of the investigation. A summary of the most important findings including trends and patterns emerging from analysis of the results. Discussion An explanation why calculations were used if any, and their link to the and investigation. Conclusion A very brief description stating whether the investigation has supported/falsified the hypothesis. A description and an explanation of how the results relate to the expectations based on laws, theories, relationships, patterns, and models studied. This section should be concluded by a closure of all findings. This section should include: A list of procedural/sources of errors that may have affected the result. Evaluation and A list of improvements and any other experiments which can be done to references support the conclusions. All sources cited in the text should be listed in full. A basic format should be used when listing the sources. Source: https://www.um.edu.mt/__data/assets/pdf_file/0007/509191/SEC062025Resources.pdf 28 Chemistry Year 9 Textbook 29 Chemistry Year 9 Textbook 2 Gases found in air and their lab preparation (LO 2) 2.1 Gases in the Earth’s atmosphere By the end of this section, you should be able to: Identify the gases that make up the air naturally and those that may be added by humans. (E.g., nitrogen, oxygen, carbon dioxide, water vapour, noble gases, carbon monoxide, sulfur dioxide, nitrogen oxides and ozone.) (2.1a) State the approximate percentage of nitrogen, oxygen, carbon dioxide and noble gases in dry, unpolluted air. (2.2a) 2.1.1 Composition of air The composition of air varies from place to place because air is a mixture of gases. A mixture is made up of two or more substances mixed together, that can be separated by physical means. The composition by volume of a typical sample of air is as follows: GAS PERCENTAGE VOLUME Nitrogen 78 % Oxygen 21 % Clean dry air Carbon dioxide 0.03 % Noble gases * Approximately 1 % (Argon, neon, helium, krypton, xenon) Humidity Water vapour Variable Impurities or pollutants (e.g., sulfur dioxide (SO2), Air pollution Variable oxides of nitrogen (NO and NO2), carbon monoxide (CO), ozone (O3), etc.) * The most abundant of the noble gases is argon which amounts to 0.9%. The composition of air is mainly affected by the following factors: respiration by all living things, in which oxygen is taken in and carbon dioxide is given out to the atmosphere. photosynthesis (the way plants build up their food using sunlight) in which carbon dioxide is taken in and oxygen is given out to the atmosphere. decay (when living things die and are consumed by microorganisms) in which carbon dioxide is released. volcanic activity in which water vapour, carbon dioxide and other impurities (sulfur dioxide and hydrogen sulfide) are released when a volcano erupts. human activity involving burning of fossil fuels, in which carbon dioxide and water vapour are produced as well as other pollutant gases such as sulfur dioxide and oxides of nitrogen. 30 Chemistry Year 9 Textbook 2.1.2 Measuring the percentage of oxygen in air By the end of this section, you should be able to: Determine experimentally the percentage oxygen in air. (2.3a) During combustion reactions, substances react with oxygen to form oxides. The following experiment can be used to measure the percentage of oxygen found in air. 1. Place an excess of red-brown copper turnings in a hard glass tube connected to two gas syringes one on each side. 2. Check that the apparatus is airtight by pushing the air from one syringe to the other for several times. 3. Pass 100 cm3 of air over the heated copper turnings by pushing the plunger to and fro until the volume in the gas syringes does not change. 4. Leave the syringes to cool to room temperature before taking any readings since air expands on heating and a higher value would be obtained if read at a high temperature. Volume of air at the start (cm3) Volume of air at the end (cm3) Volume of oxygen used (cm3) 100 79 21 Therefore, the percentage of oxygen gas in the air is: 21 × 100 = 21% 100 In this experiment the reactive part of air, i.e. oxygen, is reacting with copper to form black copper(II) oxide, as shown in the equation below. copper + oxygen → copper(II) oxide 2Cu(s) + O2(g) → 2CuO(s) Measuring the percentage of oxygen in air. 31 Chemistry Year 9 Textbook 1. Fill in the table below with the composition by volume of a typical sample of air. Gas Percentage volume Nitrogen Oxygen Carbon dioxide Noble gases (argon, neon, helium, krypton, xenon) Water vapour Impurities or pollutants (e.g., NOx, SO2, etc) 2. Indicate whether the following statements are true or false. Correct the false statements. a. The air is mainly a mixture of two gases – hydrogen and oxygen. T/F b. Component gases of clean air are carbon dioxide, water vapour, noble gases, and sulfur dioxide. T/F c. The composition of air varies from place to place. T/F d. The most abundant of the noble gases in air is neon. T/F e. Burning fossil fuels contribute to the amount of carbon dioxide, sulfur dioxide and oxides of nitrogen in the atmosphere. T/F f. Oxygen takes up one fourth of air. T/F 3. The apparatus shown below is used to estimate the proportion of oxygen in the atmosphere. Copper is present in excess. A volume of dry air (90 cm3) is passed backwards and forwards over heated copper until no further change in volume takes place. The apparatus is then allowed to cool down to room temperature and the final volume reading is taken. Some typical results are shown below. Volume of gas before passing over heated copper = 90.0 cm3 Volume of gas after passing over heated copper = 70.7 cm3 During the experiment the copper slowly turned black. a. Explain why it is important that copper is present in excess quantity. b. Explain why the apparatus is allowed to cool back to room temperature before the final volume reading is taken. c. Using the information given above, calculate the reduction in volume in the gas syringes at the end of the experiment. d. Explain why there is a change in volume. e. Calculate the percentage reduction in volume. f. Would you expect the copper to have increased or decreased in mass during the experiment? Explain your answer. g. Write a word equation for the reaction taking place. h. Give the name of the main residual gas at the end of the experiment. 32 Chemistry Year 9 Textbook 2.1.3 Properties and uses of the gases in dry air By the end of this section, you should be able to: Describe the properties of nitrogen, oxygen, carbon dioxide and noble gases. (2.1b) Relate the properties of nitrogen, oxygen, carbon dioxide and noble gases to their uses. (2.2b) 2.1.3.1 Nitrogen – properties and uses Nitrogen is the most abundant gas in air. The following include some of nitrogen’s properties. It is a colourless and odourless gas. It is a neutral gas (pH 7). It is slightly soluble in water. It has a similar density to air. (N2 = 1.25 g/l; air = 1.29 g/l at STP) It is very unreactive compared with oxygen. Nitrogen also combines with oxygen at high temperatures to form oxides: nitrogen monoxide (NO) and nitrogen dioxide (NO2). This reaction occurs naturally in the air due to lightning during thunderstorms, as well as inside running car engines and power station furnaces. Nitrogen is used in the following situations. Liquid nitrogen is very cold. It boils at -196 °C. It is used to quick-freeze food in food factories. Liquid nitrogen is often used as a refrigerant. It is used for storing sperm, ova, and other cells for medical research and reproductive technologies. It is also used in hospitals to store tissue samples. Due to its lack of reactivity, nitrogen gas is flushed through food packing to remove oxygen and keep Source: https://www.thoughtco.com/liquid- nitrogen-facts-608504 the food fresh for a longer period of time. To produce ammonia when combined with hydrogen under special conditions. Further reading on facts and properties of liquid nitrogen. Daniel Rutherford and the ‘property’ of nitrogen The Scottish chemist, Daniel Rutherford, isolated nitrogen gas from air in 1772. He was a student of Joseph Black, who discovered the presence of CO 2 in air. Rutherford carried out experiments that removed the oxygen and carbon dioxide present in air. He noticed that living things could not survive in the remaining gas. This gas was later named nitrogen. 33 Chemistry Year 9 Textbook 2.1.3.2 Oxygen – properties and uses Oxygen has the following properties. It is a colourless and odourless gas. It is a neutral gas. It is slightly soluble in water; in fact it supports aquatic life. It is slightly denser than air. (O2 = 1.43 g/l; air = 1.29 g/l at STP) It is a reactive element, combining vigorously with many metals (e.g., sodium, magnesium, copper) and non-metals (e.g., carbon, sulfur). It supports combustion. Oxygen is used in the following situations. Required during combustion reactions. As an aid to breathing where the natural supply of oxygen is insufficient. For example, in high-altitude flying or climbing, and when anaesthetics are administered to a patient. In the oxyacetylene (oxygen-ethyne) torch, which can be used for welding and for cutting very thick steel plates. The temperature of the flame reaches about 3200 °C. For making steel. In sewage treatment. If it were not for this treatment, many rivers and lakes would be spoiled by sewage. Further reading on facts about oxygen. Properties of oxygen - John Mayow John Mayow, born in England in 1640, was one of the first scientists who identified the nature of air. Through his work, he established that air was not composed of a single element, but of different substances. Mayow showed that combustion was supported by only a part of air and this same portion was responsible for respiration. Mayow, wrote on the function of oxygen in respiration almost a hundred years before oxygen was discovered. 2.1.3.3 Carbon dioxide – properties and uses Carbon dioxide has the following properties. It is a colourless, odourless gas. It is an acidic gas because it is slightly soluble in water, forming carbonic acid, H2CO3. It is denser than air (CO2 = 1.96 g/l; air = 1.29 g/l at STP). Things will not burn in it (it does not support combustion). It is not poisonous but does not support respiration. 34 Chemistry Year 9 Textbook Carbon dioxide is used in the following situations. It is taken up by plants during the process of photosynthesis. It is used in the production of sparkling mineral water, fizzy drink, and beers. It is used in fire extinguishers. It is used as a coolant. Carbon dioxide in the form of dry ice is used in the winemaking industry. Dry ice is solid carbon dioxide, and it is used to cool down gr

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