Integrated Science Notes 2023 PDF

Integrated Science Notes 2023 Secondary 2/ Year 2 Chapter 7.1 Chemical Changes NAME CLASS 2 INDEX NO. TEACHER 1  Contents...

Integrated Science Notes 2023 Secondary 2/ Year 2 Chapter 7.1 Chemical Changes NAME CLASS 2 INDEX NO. TEACHER 1  Contents Page Glossary of Terms & Learning Outcomes 2 7.1 Chemical Changes 7.1.1 Identifying a Chemical Change 3 7.1.2 Types of Chemical Changes A) Mixing 3 - Acid reactions B) Heating 4 - Thermal Decomposition - Combustion C) Exposure to light 4 - Photosynthesis D) Interaction with oxygen 4 - Rusting - Respiration E) Using an electrical current 5 - Electroplating At the end of this topic, you will be able to: (a) identify chemical and physical changes based on attributes in a reaction (b) identify the different types of chemical changes (c) describe how chemical changes occur (d) state the importance of chemical changes in our daily lives 2 7.1 Chemical Changes 7.1.1 Identifying a Chemical Change Recall: Chemical Change – a change in which new substance is formed Physical Change – a change in which no new substances are formed The table below shows the characteristics of a physical and chemical change. Chemical Change Physical Change New substances are formed. No new substances are formed. - Change in the properties of substance (eg - No change in the properties of substance color, magnetic properties, electrical conductivity, etc) Energy in the form of heat/light is produced (in No heat/light produced some reactions only) Reactions are usually irreversible. Reactions are usually reversible. Can be separated using physical changes (eg filtration, evaporation to dryness, distillation etc) Read pages 60 – 65 of Textbook 2A to understand chemical changes 7.1.2 Types of chemical changes Chemical changes can occur due to various reasons. Listed here are some of the ways that result in chemical reactions and some types of chemical reactions. A) Mixing (Chemical reactions that occurs when 2 or more reactants are mixed together) 1. Acid reactions Eg: acid + metal  salt + hydrogen acid + base  salt + water acid + carbonate  salt + carbon dioxide + water Read Pg 66 – 78 of Textbook 2A 3 B) Heating (Reactions in which heat or increase in temperature is necessary) Heating may bring about the decomposition of some substances. These reactions are called thermal decomposition. 1. Thermal decomposition heat Eg: Calcium carbonate calcium oxide + carbon dioxide Another example of a reaction that can be brought about by heating is combustion (or burning). Combustion refers to the combination of a substance with oxygen in the presence of heat. 2. Combustion heat Eg: petrol + oxygen carbon dioxide + water Importance to daily lives: Heating brings about essential chemical reactions especially when cooking where the flavours are released by various ingredients eg caramelization of sugar Combustion is used daily in cars, when petrol undergoes combustion to release more heat energy to power a car. Can you think of some harmful effects of combustion? C) Exposure to light (Reactions that only occur when light is present) 1. Photosynthesis light Word equation: carbon dioxide + water glucose + oxygen Importance to daily lives: Apart from the crucial role that plants play in maintaining the levels of carbon dioxide and oxygen in the atmosphere, photochemical reactions are used in X-ray films, photographic films and more, where silver bromide decomposes in the presence of light to form silver and bromine. D) Interaction with oxygen (Oxidation) (For any reactions involving oxygen) 1. Rusting *(Note that rusting is only for iron. Other metals corrode when reacted with oxygen) Eg: iron + water + oxygen  hydrated iron(III) oxide For rusting to occur, moisture and oxygen must be present to form rust (hydrated iron (III) oxide) 2. Respiration Eg: Glucose + oxygen  carbon dioxide + water Importance to daily lives: In a tropical climate like Singapore, rusting is a common occurrence. As such, knowing the substances that are crucial for rusting allows us to find ways to prevent rusting. Eg: covering the iron with a layer of paint/oil to prevent it coming into contact with oxygen/moisture 4 E) Using an electric current (Some chemical reactions occur when an electric current is passed through) 1. Electroplating – coating an object with a metal by passing an electric current through a solution. Electroplating is used to coat items like trophies or coins with a thin layer of metal. Importance to daily lives: This process allows us to coat many different types of surfaces with a thin layer of metal with the help of electrochemical process. This results in a wide range of applications from the making of jewelry (aesthetic) to other manufacturing industry for protection purpose and also in the medical field. The RISIS orchid was pioneered in Singapore since 1976. We were the first to discover a way to encapsulate natural orchids in gold. Other uses include coating a thin layer of non-corrosive metal to prevent corrosion on metal appliances that corrode easily. Computers, cell phones and other electronic devices use good conductors of electricity such as gold and silver. But these elements are costly, hence by coating a thin layer of these metals helps to increase the conductivity of the circuits. Gold plating is also employed to create tooth inlays and aid in various dental procedures. Implanted parts such as replacement joints, screws, and plates are frequently electroplated to make parts more corrosion-resistant and compatible with pre-insertion sterilization. Medical and surgical tools, including forceps and radiological parts, are also commonly electroplated. 5 [Enrichment] Watch these videos if you are interested to know how electroplating works Copper Electroplating Experiment https://youtu.be/gTjWkeSpRqk Electroforming Tutorial - Gold Plating on Plastic Electroplating https://youtu.be/Zxd_uzRW3OM How does Electroplating Work https://youtu.be/OxhCU_jBiOA Examples of Chemical Reactions in Everyday Life Here are some broad examples of chemical reactions in daily life. 1. Combustion 2. Photosynthesis 3. Aerobic cellular respiration 4. Anaerobic respiration (including fermentation) 5. Oxidation (including rust) 6. Electrochemistry (including chemical batteries) 7. Digestion 8. Acid-base reactions 9. Cooking 10. Fireworks 11. Rotting of food 12. Electroplating metals 6