Year 8 Practice Two IB Middle Years Chemistry PDF

Aga Khan Academy Mombasa year 8 practice two IB Middle Years Chemistry Grade: Grade 9 Criteria: A 124 B 114 C 109 D 25 Total: 372 points Authors: Fred Machel Bongu Page 1 of 146 Section 1 No items in this...

Aga Khan Academy Mombasa year 8 practice two IB Middle Years Chemistry Grade: Grade 9 Criteria: A 124 B 114 C 109 D 25 Total: 372 points Authors: Fred Machel Bongu Page 1 of 146 Section 1 No items in this section Page 2 of 146 Task 1 Q 2.1 The Modern Periodic Table of Elements is arranged by A1 A. atomic mass B. atomic number C.valence electrons D. number of isotopes A A B B C C D D Q 2.2 Which is an alkali metal? A1 A. Magnesium B. Iron C. Sodium D. Europium A A B B C C D D Page 3 of 146 Q 2.3 Elements in a..................have similar chemical properties. A1 A. period B. group C. row A A B B C C Q 2.4 As you move down a group, atomic radius increases because - A1 A. you add more and more neutrons B. you add more and more protons C. you add more and more shells (energy levels) D. you add more atomic mass A A B B C C D D Page 4 of 146 Q 2.5 Elements in the same column of the periodic table always have the same # of A1 _______ as one another. A. Protons B. Neutrons C. Electrons D. Valence Electrons A A B B C C D D Page 5 of 146 The Periodic Table The periodic table shows the positions of metals, non-metals and metalloids. Metals tend to lose electrons and so they form cations. Non-metals tend to gain electrons so they form anions. Elements in a group have the same oxidation state and therefore similar chemical properties. Page 6 of 146 Q 3.1 A6 Page 7 of 146 Teacher's Explanation Page 8 of 146 Q 3.2 A2 Teacher's Explanation Page 9 of 146 Q 3.3 A1 Teacher's Explanation Q 3.4 A2 Teacher's Explanation Page 10 of 146 Q 3.5 A3 Teacher's Explanation Page 11 of 146 Atomic Number Q 4.1 A1 Teacher's Explanation Atomic number Q 4.2 A1 Teacher's Explanation Page 12 of 146 Page 13 of 146 Q 4.3 A5 Teacher's Explanation Page 14 of 146 Criterion BC A group of students wanted to find out the if there is any effect on change of state at different places. They decided to climb a mountain and did the experiment at 5 diffrent places as they climbed up. This is how they did the experiment: A sample of pure substance called X was slowly heated from –5.0 °C, which is below its melting point, to 90 °C, which is above its boiling point. Its temperature is measured every minute and the results are represented on the graph. Q 5.1 B2 State a research question for this experiment. {level 1-2 Teacher's Explanation What is the effect of change in altitude/height in the melting point of substance X? Page 15 of 146 Q 5.2 B2 Describe the independent variable [level 3-4] Teacher's Explanation Change of height or altitude the experiment was done at 5 different locations which had different height above sea level At the bottom of the mountain, then 3 other locations each 1000metere or IKm apart going up the mountain Q 5.3 B2 Describe the dependent variable Teacher's Explanation The DV was the melting point measured using a thermometer in oC The temperature was recorded when all substance x has melted This was repeated 3 times at each location the results were recorded in a table for easy reference and presentation Q 5.4 B2 Suggest one control variable Teacher's Explanation amount of substance used should be constant, say 5g each time. if different amounts are used, it will not be a fair test Page 16 of 146 Q 5.5 C2 Suggest an explanation why the temperature stays the same between B and C as shown in the graph. Teacher's Explanation Heat is being absorbed to change state. Q 5.6 C2 Describe a weakness in this investigation and suggest how it might be improved Teacher's Explanation One minute is too long to wait to measure change in temperature. Something might have changed between the next minute. It would be better to measure every 30 seconds or use a data logger connected to a laptop so that the temperature is measures throughout. Page 17 of 146 Criterion A Page 18 of 146 Q 6.1 A3 a. Identify the name of the row with the elements Li to Ne in the Periodic Table above. (level 1-2) b. State the element with the smallest radius in this row of Li to Ne. (Level 3-4) c. Suggest the reason this element has the smallest atomic radius. (Level 5-6) Teacher's Explanation a. Period 2 b. Neon c. Due to the increasing effective nuclear charge which increases across the period attracting the shells more strongly, an electron is added as we move across but goes to the same shell therefore the ENC is stronger reducing the size of the atom across. Page 19 of 146 The following poem by Vernon Newton is called "Mistress Fluorine" Fervid Fluorine, though just nine Knows her aim in life: combine! In fact, of things that like to mingle, None's less likely to stay single. Page 20 of 146 Q 6.2 A1 Of the halogens in the periodic table above, state which element has the smallest radius. (level 1-2) A Br B At C Cl D F Teacher's Explanation D Q 6.3 Describe the trend of atomic radius from Li to K in the periodic table above. (level 5- A1 6) Teacher's Explanation The atomic radius of atoms generally increases from top to bottom within a group. Li has only two energy levels, 2.1 so it is has a small atomic radius; while K has 4 energy levels 2.8.8.1 hence it has a large atomic radius Page 21 of 146 Q 6.4 Explain why the halogens in Group VII have similar chemical properties. (Level 7-8) A1 Teacher's Explanation all have 7 electrons in their outer shell all react by gaining one electron Q 6.5 A1 The diagram above illustrated a relationship between electrons in an atom. Describe the trend in this relationship down a group in the periodic table. (level 5-6) Teacher's Explanation The diagram shows shielding effect which increases down a group because the number of energy level increases hence more repulsion between electrons further down a group. Page 22 of 146 Q 6.6 A3 Interpret this information to make scientifically supported judgments about the chemistry of fluorine. ( hint: make as many conclusions as you can form the information given) (level 7-8) Teacher's Explanation Has atomic number 9 electron configuration 2.7 very reactive gains 1 electron most reactive halogen because of small size, therefore, attracts electrons easily. reactivity decreases down the group Page 23 of 146 Models (Criterion B) As a scientist, an industry has requested you to determine the rate of a reaction that is used to make carbon dioxide. The industry uses limestone (calcium carbonate) and hydrochloric acid to produce carbon dioxide. CaCO3 + 2HCl --> CaCl2 + H2O + CO2 You are given a set up of apparatus shown below. Page 24 of 146 Q 7.1 B1 The limestone (calcium carbonate) used in the factory is brought in from the mine in different sizes. State a research question that you can investigate based on a factor that affects the rate of a reaction. (level 1-2) Teacher's Explanation How does change in size of calcium carbonate affects the rate of a reaction with hydrochloric acid. How does change in surface area affect the rate of a reaction Q 7.2 B1 State hypothesis that can be tested in this investigation. (Level 1-2) Teacher's Explanation Increasing the sizes of calcium carbonate used in the reaction with hydrochloric acid will reduce the rate of production of carbon dioxide. Increasing the surface area of calcium carbonate by reducing the sizes will increase the rate of reaction with hydrochloric acid. Page 25 of 146 Q 7.3 B1 Describe the independent variable in this investigation. ( Level 3-4) Teacher's Explanation Independent variable is the different sizes of calcium carbonate Independent variable is change in surface area Q 7.4 B1 Describe the dependent variable in this investigation. (Level 3-4) Teacher's Explanation Dependent variable is the rate of reaction measured by recording the volume of carbon dioxide produce per second or minute. Q 7.5 B1 Describe a safety measure you will observe while carrying out the investigation. (Level 5-6) Teacher's Explanation Wear a lab coat or gloves to protect skin from the hydrochloric acid Wear goggles to protect eye from spillage or particles of calcium carbonate Page 26 of 146 Q 7.6 B1 Describe an environmental issue you will observe in this investigation. (Level 5-6) Teacher's Explanation Carbon dioxide, CO2 produced is a green house gas, so only little amount should be produced. So I will use small amounts of calcium carbonate Calcium carbonate is mined, so I will use very little amount. Waste such as calcium chloride should not be poured directly into the sink but into a chemical waste container to be disposed properly by laboratory technician or recycled Q 7.7 B2 Explain why it is important to repeat an investigation several times. (Level 7-8) Teacher's Explanation Replication lets you see patterns and trends in your results. The more times an experiment is repeated, the more anomalies stick out and can be discounted. Too check for anomalies and to show that the results is not by luck or random. If you repeat it many times then the data is considered more reliable as the chance of it all being down to luck or random is reduced. Page 27 of 146 Q 7.8 B2 Suggest another method you could use to measure the rate in this investigation. ( Level 7-8) Teacher's Explanation Use a weighing balance to measure change in mass per second or minute Page 28 of 146 Patterns Q 8.1 A1 A Choice A B Choice B C C Teacher's Explanation B Page 29 of 146 Q 8.2 A1 A Choice A B Choice B C C Teacher's Explanation C Page 30 of 146 Q 8.3 A1 A Choice A B Choice B C C Teacher's Explanation A Page 31 of 146 Q 8.4 A1 A Choice A B Choice B C C Teacher's Explanation A Page 32 of 146 Q 8.5 A1 A Choice A B Choice B C C Teacher's Explanation B Page 33 of 146 Q 8.6 A1 A Choice A B Choice B C C Teacher's Explanation B Page 34 of 146 Q 8.7 A1 A Choice A B Choice B C C Teacher's Explanation C Page 35 of 146 Q 8.8 A1 A Choice A B Choice B C C Teacher's Explanation C Page 36 of 146 Q 8.9 A1 A Choice A B Choice B C C Teacher's Explanation A Page 37 of 146 Q 8.10 A1 A Choice A B Choice B C C Teacher's Explanation B Page 38 of 146 Q 8.11 A1 A Choice A B Choice B C C Teacher's Explanation B Page 39 of 146 Q 8.12 A1 A Choice A B Choice B C C Teacher's Explanation A Page 40 of 146 Q 8.13 A1 A Choice A B Choice B C C Teacher's Explanation B Page 41 of 146 Q 8.14 A1 A Choice A B Choice B C C Teacher's Explanation B Page 42 of 146 Q 8.15 A1 A Choice A B Choice B C C Teacher's Explanation C Page 43 of 146 Q 8.16 A1 A Choice A B Choice B C C Teacher's Explanation C Page 44 of 146 Periodic table Q 9.1 C1 Identify a pair of letters which represents elements that are in the same period. A Choice A B Choice B C Choice C D Choice D Teacher's Explanation D Page 45 of 146 Q 9.2 Identify which row shows the correct number of protons and electrons in the ion of C1 an element in Group II of the Periodic Table. A Choice A B Choice B C Choice C D Choice D Teacher's Explanation B Page 46 of 146 Q 9.3 C1 State what determines the order of the elements in the Periodic Table. Teacher's Explanation atomic number / number of protons ignore: number of electrons Periodic trend Q 9.4 A2 Explain the ionic radii for elements across period 3 shown in the diagram above. Teacher's Explanation Ionic radius decreases moving from left to right across a period. This is because metals lose electrons to form ions hence ending up with more protons so the positively charged nucleus draws in the electrons more tightly. But, for the non-metallic elements, ionic radius increases because there are more electrons than protons as non-metals form ions by gaining electrons Page 47 of 146 Periodic table Q 10.1 C1 Identify a pair of letters which represents elements that are in the same period. A Choice A B Choice B C Choice C D Choice D Teacher's Explanation D Page 48 of 146 Q 10.2 Identify which row shows the correct number of protons and electrons in the ion of C1 an element in Group II of the Periodic Table. A Choice A B Choice B C Choice C D Choice D Teacher's Explanation B Page 49 of 146 Q 10.3 C1 State what determines the order of the elements in the Periodic Table. Teacher's Explanation atomic number / number of protons ignore: number of electrons Periodic trend Q 10.4 A2 Explain the ionic radii for elements across period 3 shown in the diagram above. Teacher's Explanation Ionic radius decreases moving from left to right across a period. This is because metals lose electrons to form ions hence ending up with more protons so the positively charged nucleus draws in the electrons more tightly. But, for the non-metallic elements, ionic radius increases because there are more electrons than protons as non-metals form ions by gaining electrons Page 50 of 146 Atomic structure Q 11.1 A3 Teacher's Explanation The table shows some information about six particles. Page 51 of 146 Q 11.2 A1 State the nucleon number for particle A Teacher's Explanation 85 Q 11.3 A1 Explain why particle B is a negative ion. Teacher's Explanation Has more electrons than protons Q 11.4 A2 Which two atoms are isotopes of the same element?........................... and........................... Explain your answer. Teacher's Explanation C and E (1) Same number of protons but different number of neutrons (1) Page 52 of 146 These tasks explores evidence as a related concept Q 12.1 A1 State what is meant by the term isotopes. Teacher's Explanation Atoms with same number of protons and different number of neutrons / atoms with same atomic number and different mass number Q 12.2 A3 Number neutrons Number of protons Electronic configuration Teacher's Explanation number of neutrons 17 number of protons 16 electronic configuration 2.8.6 Page 53 of 146 Q 12.3 A1 Sulfur has a low melting point and does not conduct electricity. Explain why sulfur has a low melting point. Teacher's Explanation Weak intermolecular forces / weak attraction between molecules Q 12.4 A1 Explain why sulfur does not conduct electricity. Teacher's Explanation No free electrons / no delocalised electrons / all electrons used in bonding / no mobile electrons Page 54 of 146 This question is about bonding, structures and properties. The box gives four types of structure. The table shows some properties of four substances, A, B, C and D. Page 55 of 146 Q 12.5 A2 Complete the table by giving the correct type of structure for each substance. You may use each structure once, more than once or not at all. A B C D Teacher's Explanation A simple molecular B giant covalent C giant metallic D giant ionic All 3 to 4 correct 2 marks 1 to 2 correct options 1 mark. Page 56 of 146 A group of students tested electrical conductivity of a range of solids and liquids using the apparatus below. The students recorded their results in the table below. Page 57 of 146 Q 12.6 A2 Explain the difference in conductivity between sodium chloride solution and sodium chloride solid. Teacher's Explanation When sodium chloride is dissolved in water, the solution conducts very well, because the solution contains ions. The solution of sodium chloride contains sodium ions, which have a positive charge, and chloride ions, which have a negative charge. However, sodium chloride in solid state has no free ions. The ions are held tightly by strong electrostatic bonds. Q 12.7 A1 Explain the observation recorded for graphite. Teacher's Explanation Graphite is a good conductor of electricity because it contains delocalised (free) electrons. These electrons are free to move through the structure of the graphite. Q 12.8 A1 Suggest the difference in conductivity between distilled water and tap water. Teacher's Explanation Tap water contains dissolved salts in it. These salts dissociates into ions when electricity passed through it which are responsible for the electricity conductivity of tap water. But distilled water does not contain any dissolved salts, so it does not conduct electricity. Page 58 of 146 Interaction is the related concept explored in these question A group of Y9 students conducted an investigation using the information below. Data Table Element Group Atomic radius (10-12m) Li 1 130 Na 1 160 K 1 200 Q 13.1 B1 State a research question that the students used to guide the investigation. Teacher's Explanation How does change in atomic radius affect reactivity of alkali metals with water? Page 59 of 146 Q 13.2 B1 State an hypothesis that the student tested in this investigation. Teacher's Explanation Reactivity of alkali metals is directly proportional to atomic radius As the atomic radius increases, the reactivity of alkali metals with water increases. Q 13.3 B1 Describe independent variable in this investigation. Teacher's Explanation Atomic radius of alkali metals Q 13.4 B1 Describe dependent variable in this investigation. Teacher's Explanation Time taken for 1g of each metal to react completely with water. Page 60 of 146 Q 13.5 B2 Describe two control variables that the students kept constant for fair test. Teacher's Explanation Volume of water used should be the same for a fair test Mass of alkali metal used Q 13.6 B1 State a safety precaution that is necessary in this investigation. Teacher's Explanation Wear lab coat to protect against accidental spills, Wear goggles, or safety glasses to protective eyes protect the area surrounding the eye in order to prevent particulates, water or chemicals from striking the eyes. Wear gloves to protect against chemicals, Q 13.7 B3 Describe how the investigation was carried out by the students Teacher's Explanation 1. Pour a fixed volume of water in the water trough. 2. Place 1g of lithium on the water surface. 3. Time how long it takes for the metal to react completely with water 4. Repeat at least three times 5. Repeat for Na and K Page 61 of 146 Q 13.8 C1 Suggest an improve that the students could make in order to collect enough data. Teacher's Explanation Increase the number of alkali metals to 5 in order to have five data points. Page 62 of 146 Periodic table Q 14.1 A2 Use the correct words from the box to complete the sentence. electrons ions protons neutrons shells The nucleus of an aluminium atom contains.............................. and............................... Teacher's Explanation protons neutrons any order allow proton allow neutron Page 63 of 146 Q 14.2 A1 Complete the sentence. In the periodic table, aluminium is in Group.............................. Teacher's Explanation three Page 64 of 146 Q 14.3 A1 The symbol means that aluminium can be recycled. It does not show the correct chemical symbol for aluminium. State the correct chemical symbol for aluminium...................................................... Teacher's Explanation Al Page 65 of 146 Q 14.4 D2 State two reasons why aluminium should be recycled. Teacher's Explanation any two from: limited resource expensive in terms of energy / mining effects on the environment, such as, landfill, atmospheric pollution, quarrying Q 14.5 D2 Aluminium has a low density, conducts electricity and is resistant to corrosion. Which one of these properties makes aluminium suitable to use as kitchen foil? Give a reason for your answer. Teacher's Explanation resistant to corrosion does not react (with water or food) Page 66 of 146 Atomic Structure This question is about atomic structure and elements. Q 15.1 A2 Complete the sentences. The atomic number of an atom is the number of............................................................. The mass number of an atom is the number of.......................................................................................................................................................................................... Teacher's Explanation protons protons and neutrons Q 15.2 A2 Explain why an atom has no overall charge. Use the relative electrical charges of sub-atomic particles in your explanation. Teacher's Explanation (because the relative electrical charges are) –(1) for an electron and +(1) for a proton and the number of electrons is equal to the number of protons Page 67 of 146 Q 15.3 A2 Explain why fluorine and chlorine are in the same group of the periodic table. Give the electronic structures of fluorine and chlorine in your explanation. Teacher's Explanation (the electronic structure of) fluorine is 2,7 and chlorine is 2,8,7 (so fluorine and chlorine are in the same group) because they have the same number of or 7 electrons in their highest energy level or outer shell Page 68 of 146 Q 15.4 C1 What is the chemical symbol of this non-metal? Teacher's Explanation S Q 15.5 A2 When elements react, their atoms join with other atoms to form compounds. Complete the sentences. Compounds formed when non-metals react with metals consist of particles called................................................... Compounds formed from only non-metals consist of particles called......................................... Teacher's Explanation ions molecules Page 69 of 146 Group 1 Metals: Alkalis Q 16.1 C6 Two elements in group 1 of the periodic table are lithium and sodium. Very small pieces of lithium and sodium were reacted separately with water. Describe the similarities and differences in what is seen and in the products of the reactions. Teacher's Explanation Your answer can include any of the following: Similarities - both: float/on the surface move around effervescence/bubble/fizz decrease in size/disappear/dissolve produce hydrogen/H2 produce (metal) hydroxide/LiOH and NaOH produce alkaline solution/solution with pH greater than 7/add named indicator to the solution and correct colour change correct products shown in equations Differences: sodium more vigorous/more effervescence/moves faster melts forms ball/sphere produces a flame/catches fire/sparks Page 70 of 146 Q 16.2 C6 Group 1 of the periodic table contains the alkali metals lithium, sodium and potassium. The alkali metals show a pattern in their reactivity with water. This pattern is shown when small pieces of lithium, sodium and potassium are added separately to water. Describe the reactions and explain the pattern in reactivity. Teacher's Explanation Your answer can include any of the following: Description: effervescence/fizzing/bubbles float/on surface move produce hydrogen (may be shown in word or balanced equation) an alkaline/metal hydroxide solution (may be shown in word or balanced equation) gets smaller/disappears/dissolves reactivity increases with increasing atomic number/down the group/potassium effervesces more than sodium and lithium/potassium moves faster than sodium or lithium sodium and potassium melt/form a (silver-coloured) ball hydrogen burns when potassium/ sodium react potassium gives a lilac flame/sodium gives a yellow flame universal indicator added to water turns blue/purple Explanation: (group 1 metals) react by losing one electron electron is more easily lost with increasing atomic number/down the group electron/ outer shell is further away from nucleus/atomic radius increases/there are more electron shells with increasing atomic number/down the group more shielding (of outer electron)/less attraction between nucleus and outer electron/ more shells between outer electron and nucleus with increasing atomic number/down the Page 71 of 146 Criterion B A student is interested in the length of time that glow sticks will glow at different temperatures. The student placed identical sticks into water at various temperatures and then broke the inner tube, starting the reaction. Q 17.1 Identify the variables in this investigation. Independent variable, the dependent B4 variable, and two control variables Teacher's Explanation Page 72 of 146 Q 17.2 Formulate a suitable hypothesis for the investigation. If.... then.... because.... B3 Teacher's Explanation Q 17.3 Using the equipment above design an investigation to determine the conductivity of B3 sugar and table salt. Teacher's Explanation Insert the conductivity meter probe into a beaker containing the solution of the sample. Record the results and repeat 3 times to get at least similar readings. Page 73 of 146 Patterns Q 18.1 Describe the atomic radius from Q to T. Then explain the atomic radius trend you C2 have stated from Q to T. Teacher's Explanation Atomic radius increases from Q to T. Atomic radius increases down a group due to increase in energy level. Page 74 of 146 Q 18.2 C1 State a pair of letters that represents elements that are in the same group. A Q and T B R and S C P and S D Q and S Teacher's Explanation D Q 18.3 C1 State what determines the order of the elements in the Periodic Table. Teacher's Explanation atomic number / number of protons ignore: number of electrons Page 75 of 146 Q 18.4 A2 Explain the difference between the ionic radius of Q and R. Teacher's Explanation The ionic radius of Q is smaller than that of R. This is because metals lose electrons to form ions hence ending up with more protons so the positively charged nucleus draws in the electrons more tightly. But, for the non-metallic elements such as R, the ionic radius increases because there are more electrons than protons as non-metals form ions by gaining electrons Page 76 of 146 Q 18.5 State which group of the periodic table should this element be placed. Give a reason C2 for your answer. Teacher's Explanation Group 8 the element has 8 electrons in the outer energy level/shell Q 18.6 Lithium, sodium, and potassium are in Group 1. All these elements react with water. C2 In terms of electronic structure, explain why elements in the same group of the periodic table have similar chemical properties Teacher's Explanation elements in same group have the same number of electrons in outer shell accept energy level for shell accept a correct reference to a specific group eg (all) have one electron in outershell / (all) lose one electron (when they react) Page 77 of 146 Criterion A Q 19.1 A3 Name Charge Relative mass Proton Neutron Electron Teacher's Explanation proton, positive, 1 neutron, neutral, 1 electron, negative, zero or 1/1840, Page 78 of 146 Q 19.2 State the name of the gas produced when lithium reacts with water. A1 Teacher's Explanation Hydrogen Q 19.3 Lithium + Chlorine --> Lithium chloride A1 Balance the equation below Li + Cl2 --> LiCl Teacher's Explanation 2Li + Cl2 --> 2LiCl Q 19.4 The alkali metals are in group 1 of the periodic table. Explain in terms of electrons A1 why the alkali metals are in group 1. Teacher's Explanation Alkali metals have one electron in the last energy level/shell. Page 79 of 146 Q 19.5 State the period of the periodic table in which this element should be placed in. A2 Explain your answer. Teacher's Explanation Period 6 It has 6 energy level or shells Page 80 of 146 Criterion B Content type: Video This item includes interactive content. Please refer to the digital version of this assessment to view this item. Q 20.1 A group of Y9 students watches the video above to investigate how changes in atomic B2 radius affect the reactivity of the alkali metals down the group. State the independent and the dependent variable in this investigation. Teacher's Explanation IDV = atomic radius DV = reactivity of the metals Q 20.2 Suggest two control variables in this investigation. B2 Teacher's Explanation (i) The volume of water should be the same (ii) The size/mass of the metal used should be the same Page 81 of 146 Q 20.3 Suggest two apparatus that can be used to measure to measure the control variable B2 Teacher's Explanation ((i) measuring cylinder (ii) weighing balance Q 20.4 Suggest two safety precautions that should be observed when reacting Alkali metals B2 with water in a school laboratory. Teacher's Explanation (i) wear safety goggles to protect the eyes (ii) wear the gloves to protect their hands from the alkali solution (iii) wear the laboratory coat to protect the clothes and skin Page 82 of 146 Criterion B Content type: Video Displacement reactions of the halogens As the outer shell becomes further from the nucleus. the force of attraction between the nucleus and the outer shell decreases. As a result, the halogen becomes less reactive. This item includes interactive content. Please refer to the digital version of this assessment to view this item. Q 21.1 State a research question that can be investigated using the information in the video B1 and the statement above. Teacher's Explanation How does a change in atomic radius affect the reactivity of the halogens? Page 83 of 146 Q 21.2 Describe the independent and dependent variables in your research question. B2 Teacher's Explanation IDV = the change in atomic radius which increases down the group DV = reactivity of the halogens which decreases as the atomic radius increases Q 21.3 Suggest two control variables in this investigation B2 Teacher's Explanation Use the same volume of the halogens in the reaction Use the same concentrations of the halogens Q 21.4 State the name of the apparatus that can be used to measure the control variable B1 mentioned above. Teacher's Explanation Measuring cylinder to measure the volume of solution Page 84 of 146 Q 21.5 Suggest safety precautions that should be observed while carrying out displacement B2 reactions. Teacher's Explanation Carry out the reactions in a fume cupboard or an open area that is well-ventilated because halogen fumes are poisonous. wear gas mask to prevent the inhaling of the halogen fumes Wear safety goggles to protect your eyes from objects or spillage wear gloves to protect hands and skin from halogen solutions which are corrosive wear lab coat to protect clothing and skin from halogen spillage Page 85 of 146 Criterion C Q 22.1 Explain improvements or extensions to the method that would benefit the scientific investigation C2 carried out as shown in the video in criterion B above. Teacher's Explanation Repeating an experiment more than once helps determine if the data was a fluke, or represents the normal case. Q 22.2 State and explain the trend of atomic radius down group 17, the halogens. C2 Teacher's Explanation The atomic radius (atomic size) of the halogens increases gradually down the group. Reason: The number of shells occupied with electrons increases down the group. Page 86 of 146 Q 22.3 Suggest a relationship between atomic radius and reactivity of the halogens down C2 the group. Teacher's Explanation As you go down the group the reactivity of the halogens decreases because they increase in electron shells; so the atoms are larger as you go down the group. Therefore, the attraction of the outer electron to the nucleus decreases as you go down group 17 Page 87 of 146 Criterion C Q 23.1 Explain improvements or extensions to the method that would benefit the scientific investigation C2 carried out as shown in the video in criterion B above. Teacher's Explanation Repeating an experiment more than once helps determine if the data was a fluke, or represents the normal case. Q 23.2 State and explain the trend of atomic radius down group 17, the halogens. C2 Teacher's Explanation The atomic radius (atomic size) of the halogens increases gradually down the group. Reason: The number of shells occupied with electrons increases down the group. Page 88 of 146 Q 23.3 Suggest a relationship between atomic radius and reactivity of the halogens down C2 the group. Teacher's Explanation As you go down the group the reactivity of the halogens decreases because they increase in electron shells; so the atoms are larger as you go down the group. Therefore, the attraction of the outer electron to the nucleus decreases as you go down group 17 Page 89 of 146 Criterion B and C Metals react with dilute acids to form a salt and hydrogen gas. A student investigated how changing the concentration of hydrochloric acid affected how fast the reaction between hydrochloric acid (HCl) and Magnesium ribbon takes to produce Magnesium chloride ( MgCl2 ) and hydrogen gas (H2) Page 90 of 146 Q 24.1 Calculate the mean for the 1.2 mol/dm3 concentration of hydrochloric acid, in the third C2 row. Teacher's Explanation 51 + 49 = 100 100/2 = 50 seconds [2 mks] but if 68 = 51 + 49 = 168 168/2 = 84 [1mk only] Q 24.2 State three apparatus that are not shown in the diagram that was used in this B3 investigation Teacher's Explanation measuring cylinder for measuring volume of the acid weigh balance for weighing magnesium ribbon stop watch for recording the time Q 24.3 State a research question that could be used to guide the investigation B1 Teacher's Explanation Does an increase in the concentration of hydrochloric acid affect the time taken to produce 30 cm3 of hydrogen gas? Page 91 of 146 Q 24.4 Describe the independent and dependent variables. B2 Teacher's Explanation IDV = Change in concentration DV = time taken Q 24.5 Suggest two control variables B2 Teacher's Explanation The volume of hydrochloric acid Mass of magnesium ribbon Q 24.6 Describe two safety precautions that could be observed during the investigation. B2 Teacher's Explanation Acids are corrosive hence one should wear gloves and a lab coat Wear goggles to protect the eye from acid spillage and objects Page 92 of 146 Q 24.7 One weakness in this investigation is hydrogen gas escaping immediately after the C2 metal is added to the acid before the stopper is fixed. Another student made a different apparatus set up as a way to improve the investigation. The set is shown below Explain how the reaction will be started in this second set up. Teacher's Explanation The thread is pulled to mix the magnesium ribbon and acid. The stopwatch is started at the same time. Page 93 of 146 Section 6 Applying Science The global context is globalization and sustainability with a focus on human impact on environment. This task (Section 6-7) addresses the key concept of system and assesses criterion D (reflecting on the impacts of Science). Hydroelectricity, or hydroelectric power, is electricity produced from hydropower Displacement in water resources development occurs as a result of three categories of dams, irrigation dams, hydropower dams, dams and reservoirs for potable water supplies (multipurpose dams combine two or all three functions), by adversely affecting people whose lands or house, or both, are submerged (in full or in part), or people whose place of employment disappears Page 94 of 146 Image 6.1 Page 95 of 146 List of Hydroelectric Power station failures Plant Country Year Power Loss Cause / Deaths Möhne Germany 1943 5.1 MW Destroyed during WWII by RAF Reservoir Lancaster Schoellkopf United 1956 One worker Destruction of the plant as it fell from Power Station States was killed the Niagara Gorge wall and collapsed into the Niagara River, caused by water seeping into the back wall of the power station. Vajont Dam Italy 1963 1917 Overtopping due to landslide caused deaths by instability of the rock around, with the evidence of the instability suppressed by the Government. Mangla Dam Pakistan 1971 1000 MW The power house was damaged due to an Indian Air Force raid during the Indo-Pakistani War of 1971. Banqiao Dam China 1975 26000 dead Flood Lawn Lake Dam United 1982 Three lives Failed in fair weather due to a States lost combination of poor construction, age, and neglect. Sayano- Russia 2009 75 Fatalities Turbine Failure Shushenskaya Dam Dhauliganga India 2013 280 MW Unprecedented flash floods in June, hydroelectric 2013 in the State of Uttarakhand station. causing the complete submergence of power house. Page 96 of 146 Q 25.1 Using the information from the task, discuss and evaluate implications of using D 13 hydroelectric power plant for electricity. In your answer you should include: Ethical Impacts on the local community while getting displaced and losing their land due to construction of hydroelectric power Economic impact of hydropower plant for State Govt. Wider Impact on the ecosystem Sustainability of Hydroelectric power plant in comparison with other renewable source of energy A concluding appraisal of all the points discussed above Page 97 of 146 Teacher's Explanation Use this to award marks Either an economical or ethical impact is 1-2 stated Impact on ecosystem is stated A statement of one economical impact on 3-4 State Govt A statement of one ethical impact on local community Environmental impact stated Sustainability of hydropower plant stated Two economical implications for State Govt 5-8 Two ethical implications on local community Two environmental impact on ecosystem Sustainability of hydropower plant compared with one renewable resources Two economical implications for State Govt, 9 - 13 with justification for one (2) Two ethical implications on local community, with justification for one (3) Two environmental impact on ecosystem, with justification for one (3) Sustainability of hydropower plant compared with two other renewable resources, with justification for one (3) A concluding appraisal (2) Page 98 of 146 Section 3 Investigating Skills This task (Sections 3-4) addresses the key concept of systems and focuses on Criterion B (Inquiring and Designing) and Criterion C (Processing and Evaluating). A group of students investigated reactions between metals and hydrochloric acid to confirm their positions on the reactivity series. Page 99 of 146 The rate of production of hydrogen gas is a consequence of the reactivity of the metal present during the reaction. They were provided with the following. Equipment Freshly polished pieces of metal of equal surface area (2 cm × 2 cm) including copper, zinc, tin, magnesium, aluminium, and iron. 1.0 mol dm-3 hydrochloric acid 250 cm3 conical flask Glass gas syringe Rubber bung Stopwatch Diagram Page 100 of 146 Q 26.1 Help them design an experiment to investigate the effect the reactivity of a metal has B 10 on the initial rate of production of hydrogen gas. In your design you must: State a hypothesis. 1 mk Identify a control variable. Describe how to control this variable. 2mks Explain how the method you have designed will enable the students to examine the initial rate of reaction and hence make a comparison between the reactivity of the metals. 5 mks Describe any two safety measures 2mks Teacher's Explanation How does IV affect DV, keeping CV constant. 3 marks IV-metal, CV-Surface area, DV-Volume of 3 marks hydrogen Using gas syringe-measure the volume -stop 3 marks watch Safety glasses, gloves etc 3 marks State a hypothesis. 1 mk A more reactive metal will produce the largest volume of hydrogen gas in a given time Identify a control variable. the volume of HCl, time taken for the reaction Describe how to control this variable. 2mks Measure the volume of HCl using a measuring cylinder, time using a stopwatch when the reaction starts and stops Explain how the method you have designed will enable the students to examine the initial rate of reaction and hence make a comparison between the reactivity of the metals. 5 mks Using a syringe attached to the conical flask as shown in the diagram, record the volume of the gas produced every 15 seconds for 4 minutes repeat 3 times for each metal calculate the average and use the results to plot a graph. Describe any two safety measures 2mks wear lab coat to protect against corrosive acid wear goggles to protect the eye from objects and spillage wear gloves to protect hands from corrosive acid Page 101 of 146 Criterion A Strand (i) Describe Scientific knowledge 1. The description below represents the development of atomic theory from Dalton’s indivisible atom to the modern atomic model. As per Dalton’s atomic theory: Atoms are smallest indivisible particles All atoms in the same element are identical Atoms can neither be created nor destroyed All atoms share identical properties including weight within an element. Q 27.1 "Atoms are smallest indivisible particles" This statement can be modified, by A1 identifying the 3 subatomic particles. Name these 3 subatomic particles Teacher's Explanation All the protons, neutrons and electrons Page 102 of 146 Q 27.2 All atoms in the same element are identical A1 Outline a reason for modification of this statement. Teacher's Explanation atoms can have isotopes which have different number of neutrons Page 103 of 146 Criterion B Make Meals in the Mountains A celebrity chef from Hyderabad is well known for her cooking skills. Hyderabad Biryani is her signature dish, which is usually made with spices, vegetables, rice, and meat. On special occasions and festival seasons, people stand in the long queue to taste her signature dish. Her competitors wanted to challenge her cooking skills, so they asked a chef to do a cooking show in different parts of India and make her signature dish “Hyderabadi Biryani”. Particularly they choose all the places located at high altitudes (1000-3000 meters above the sea level). High altitude presents several challenges when preparing certain foods. While doing her cooking shows, she noticed it takes much longer to cook dishes in the hills which are at high altitudes than in the plain areas which are at low altitudes. It also significantly affected her dish quality. She thought this problem was due to the raw materials, vegetables, and meat being from different areas. So, she brought all the raw materials and ingredients from Hyderabad, however, it did not solve the issue. Bringing her kitchen crew from Hyderabad also did not resolve the cooking issue. After hearing this problem, her friend working at the university mentioned that in higher altitudes the air pressure will drop, which lowers the boiling point of the water. Vegetables and meat cooked with moist heat take much longer to cook at high altitudes because water cannot achieve a higher temperature than its boiling point which is eventually low. Then she made slight adjustments in the cooking method and brought the original flavours of the “Hyderabad Biryani”. To understand the science behind the story, design a suitable experiment to investigate the boiling of the water in different altitudes. Page 104 of 146 Q 28.1 State the research question to be tested in this investigation. [AL 1-2] B1 Teacher's Explanation Does an increase in the altitude affect the boiling point of water? Q 28.2 Outline the independent variable used in this study. [AL 3-4] B1 Teacher's Explanation The change in altitude: 5 data points should be chosen between 1000 - 3000 meters above sea level Q 28.3 State the dependent variable in the experiment. [ AL 1-2] B1 Q 28.4 State the units of the dependent variable in the experiment. [ B1 AL 1-2] Teacher's Explanation The boiling point of water was measured using a thermometer (using 0C as units) Page 105 of 146 Q 28.5 Outline two controlled variables relevant to the experiment. [AL 3-4] B2 Teacher's Explanation The volume of water used should be the same = 100 ml Use distilled water because it is pure. Impurities affect the boiling point of water The amount of heat used should be the same = bunsen burner / portable gas burner Q 28.6 Formulate and explain a suitable hypothesis that could be tested. [AL 5-6] B1 Teacher's Explanation An increase in altitude will result in a decrease in the boiling point of water because there is less or decrease in air pressure at higher altitude Q 28.7 Describe two relevant safety considerations to carry out the experiment [AL 5-6] B1 Teacher's Explanation Wear a lab coat to protect clothing and skin from any water spillage Use heat prove gloves for handling hot apparatus Wear goggles to protect the eye from any water splattering Use a pair of tongs to hold the hot apparatus Q 28.8 Explain how sufficient and relevant data will be collected in the experiment. [AL 7-8] B1 Teacher's Explanation choose 5 altitudes as data points between 1000 - 3000 meters above sea level Repeats temperature measurements 5 times or 3 times at each altitude do obtain concordant values Page 106 of 146 Q 28.9 Explain how two controlled variables were kept constant in the experiment [AL 7- B1 8] Teacher's Explanation measure the volume of water using a 100 ml measuring cylinder Use distilled water as different waters might have some solutes in them that affect the boiling point Page 107 of 146 Criterion B Things taste and smell nice because they have lots of sugar dissolved in them and they give out perfume. Perfume is a liquid but we manage to smell it when we are some way away. A group of Y9 students decided to design an investigation to find out if the distance from the source of perfume like food or flower affects the time taken to detect the smell. Q 29.1 State a research question that the students could use in the investigation. B1 Teacher's Explanation How does the increase in the distance from the source of the perfume affect the time taken to detect the smell? Q 29.2 State and explain the hypothesis that would guide the students to carry out the B3 investigation. Teacher's Explanation Hypothesis: As the distance between a person and the source of a perfume increases, the time taken to detect the scent of the perfume will increase. Explanation: The distance between a person and a source of perfume affects the time taken to detect the scent. As the distance increases, it will become more challenging for a person to perceive the fragrance. This is because the movement of perfume molecules in the air takes time as one moves away from the source, the further the distance the more time it takes before one can smell the perfume. Page 108 of 146 Q 29.3 Explain how the variables will be manipulated to collect sufficient relevant data. B6 Independent variable.... Dependent variable.... Two control variable.... Teacher's Explanation Independent variable: distance in metres To investigate this hypothesis, the students could design an experiment where they place a person at various distances (1m, 2m, 3m, 4m, and 5m) from a controlled source of perfume, such as a cooking food. Dependent variable: time taken in seconds They would then ask the person to start and stop a stopwatch as soon as the perfume is sprayed, or food lid opened and when they smell the perfume or food. By repeating the process 5 times and recording data, the students can analyze whether their hypothesis is supported by data. Control variable Amount of perfume sprayed each time. If the amount is different, then the rate of movement of the molecules will be different. The position/height at which the perfume is sprayed should be kept constant. position and direction of the spray will affect the movement of the perfume molecules. The room should be closed and fans switched off to prevent drought or wind. The movement of air will affect the speed at which perfume molecules move. Page 109 of 146 Criterion A Knowing and understanding This task (questions 1 to 2) addresses the key concept of systems and focuses on criterion A (Knowing and understanding). The arrangement of the elements in the periodic table comes from the electronic configuration of the elements. Periodic table, in full periodic table of the elements, in chemistry, the organised array of all the chemical elements in order of increasing atomic number—i.e., the total number of protons in the atomic nucleus. Page 110 of 146 Q 30.1 A1 Select the correct terms from the given options and fill in the blanks. 1. There are 7 Periods and Groups in the periodic table. Teacher's Explanation There are seven periods and eighteen/(eight) groups in the periodic table. Q 30.2 State the family names of the following elements - A2 1. Calcium 2. Chlorine Teacher's Explanation 1. Alkaline earth metals 2. Halogens Page 111 of 146 Q 30.3 From the given elements, identify the element which has similar physical and A1 chemical properties of that of Magnesium - 12. Calcium -20, Sodium- 11, Aluminium- 13, Potassium- 19 Teacher's Explanation Calcium, since they are in the same group. Page 112 of 146 Q 30.4 A3 Teacher's Explanation Page 113 of 146 Q 30.5 A2 Use at least four points to describe this. Teacher's Explanation Page 114 of 146 Q 30.6 A1 Teacher's Explanation Page 115 of 146 Criterion D Applying science The global context is scientific and technical innovation. This task (questions address the key concept of change and assesses criterion D (Reflecting on the impacts of science). Each element possesses unique properties and characteristics, making them valuable and essential for various applications. Carbon also does an excellent job of removing trihalomethanes (THMs) from the water. THMs are a class of chlorinated chemicals which result from the interaction of chlorine and decaying organic matter in the public water supply. These chemicals are known carcinogens, and the high levels found in local water supplies have been a cause for concern in recent years. Our Carbon Adsorption Towers are in series – meaning water has to pass through both towers before moving on to the next step. We routinely change out all of the carbon in each of the tanks on an annual basis. Many will recognize the term “granular activated carbon” as it is the most common technology used in home filter systems, refrigerator filters and ice maker filters. The technology is designed primarily to remove the chlorine taste found in tap water. Unfortunately, these home systems are often poorly maintained and neglected. They will work for a while but then what happens next can be kind of scary. If the filter isn’t changed at the appropriate interval, the effectiveness of the chlorine removal will decrease and, in some cases, the contaminants in an over-loaded filter actually begin to discharge back into the water. That’s not good. And furthermore, there have been numerous instances of bacterial contamination associated with poorly maintained home filter systems. Once the chlorine is gone – there’s the risk of bacteriological growth downstream of the filter. As you answer the questions, do not copy-paste, use your own words. Page 116 of 146 Q 31.1 State how often is the carbon in each of the tanks changed out. D1 Teacher's Explanation Yearly, carbon in each of the tanks on an annual basis. Q 31.2 Explain why chlorine is used in Swimming pools. D2 Teacher's Explanation Disinfection: Chlorine is a disinfectant that sanitizes the water in swimming pools by killing bacteria, viruses, and other microorganisms that can cause diseases and infections. Preventing the growth of bacteria and algae: Chlorine also prevents bacteria and algae growth in swimming pools. Q 31.3 Suggest the risks associated with poorly maintained home filter systems. D2 Teacher's Explanation Poorly maintained home filter systems can decrease the effectiveness of chlorine removal and, in some cases, the contaminants in an over-loaded filter can actually begin to discharge back into the water. There have also been numerous instances of bacterial contamination associated with poorly maintained home filter systems. Page 117 of 146 Q 31.4 Low-cost activated carbon has been the focus of research in recent years. Agricultural C2 waste such as coconut shell, orange and banana peels are getting much attention these days. Use of the waste as a low-cost adsorbent will provide several advantages. Suggest two advantages of using this agricultural waste for activated carbon in water treatment. Teacher's Explanation recycling of waste material secondly economical – its affordable to many Q 31.5 Discuss and evaluate the implications of using carbon filters for removing chlorine D3 taste in drinking water, interacting with economic factors. Teacher's Explanation carbon filters are effective for removing chlorine taste in drinking water. They remove TMS compounds from water from water. This is good since they are carcinogenic and reduce the chance of one getting cancer, which is expensive to treat. Carbon filters may not be effective in removing all contaminants However, because they are removed yearly, carbon filters can be expensive Page 118 of 146 Criterion B Investigation skills This task addresses the key concept of systems and focuses on criterion B (Inquiring and designing) In this task you will investigate how temperature is related to the solubility of salts. Solutions are important in many areas of chemistry, as they play a critical role in a variety of processes, such as chemical reactions, purification, and separation. When a solute is added to a solvent, the kinetic energy of the solvent molecules generally overcomes the attractive forces among solute particles. The solute particles leave the surface of the solid and move into the liquid phase. If we heat the solvent, the average kinetic energies of its molecules increase. Hence, the solvent is able to dislodge more particles from the surface of the solute. The solubility of KCl in g/100 ml of water at different temperatures (in 0 °C) is given below. Temperature (°C) Solubility of KCl (g/100ml H2O) 0 3.3 20 7.3 40 13.9 60 23.8 80 37.5 100 56.3 Page 119 of 146 Q 32.1 State a research question for the given data B1 Teacher's Explanation Any reasonable RQ linking solubility with only one independent variable which is Temperature. Q 32.2 Formulate a suitable hypothesis with appropriate scientific reasoning. B2 Teacher's Explanation A hypothesis that explains IV and DV are directly proportional with a scientific explanation. More specifically "As the temperature of the solution increases, the solubility of KCl in water also increases." This hypothesis suggests that there is a positive correlation between temperature and solubility, meaning that as the temperature of the solution increases, more KCl can dissolve in the water Q 32.3 Identify the dependent, independent, and controlled variables. B4 Teacher's Explanation IV is Temperature, DV is solubility and any two controlled variables like Pressure, concentration , volume of the water 100ml, etc. Q 32.4 Design a scientific investigation to test the hypothesis mentioned. Write a safe and B3 logical method you will follow and the materials and equipment required. Teacher's Explanation Complete method fully explained and could be replicated and A relevant safety precaution linked to heating hazard Page 120 of 146 Criteria B and C Source https://www.researchgate.net/figure/Fig-1-Electrical-conductivity-meter_fig1_320427865 Conductivity is the measure of the ease at which an electric charge or heat can pass through a material. Page 121 of 146  Solutions that contain dissolved salts conduct electricity because they release charged particles into solution that are capable of carrying an electric current. Drops of NaCl Conductivity of 15cm3 of Drops of Conductivity of −1 solution in μS cm CaCl2 solution in μS cm−1 0 110 0 110 1 132 1 150 2 155 2 282 3 245 3 404 4 340 4 518 Q 33.1 State a research question for some investigation that could test the conductivity of B1 NaCl. Teacher's Explanation How does the conductivity of solution depend on the number of drops of NaCl ? Q 33.2 Using the data in the table above, formulate a suitable hypothesis that could be B2 tested. Use the sentence If........... then........ because......... Teacher's Explanation If the number of drops of NaCl solution increases, then the conductivity of the solution increases because there are more charged particles in the solution. Page 122 of 146 Q 33.3 Identify the variables : B3 Independent variable Dependent variable Control variable Teacher's Explanation Independent variable: Number of drops Dependent variable: Conductivity of the solution Control variable: Concentration of salt, temperature, volume of soluton Page 123 of 146 Q 33.4 From the data in the table, plot a suitable graph and give appropriate title to the C5 graph and label X and Y axis. Teacher's Explanation Page 124 of 146 Q 33.5 Explain which salt shows steeper graph. Justify your answer. C3 Teacher's Explanation will have a steeper graph. NaCl will give two mole ion on dissociation whereas CaCl2 will give 3 mole of ion on dissociation. Q 33.6 State one improvement in the method for collecting this data. C1 Teacher's Explanation Increase the number of drops / Use concentration instead of number of drops Page 125 of 146 Criterion C Processing and evaluating This section addresses the key concept of relationships and focuses on criterion C (Processing and evaluating). Chemists look for patterns in the periodic table to discover relationships and trends that help them to predict physical and chemical properties. Page 126 of 146 A class of MYP 9 students experimented to investigate the relationship between atomic radius and boiling points of elements, focusing on the halogen family. They obtained liquid samples of the halogens and heated them until they vaporized, recording the following data: 1. Group one heated bromine and the result was 58.8°C 2. Group two heated fluorine and the result was -188.11°C 3. Group three heated iodine and the result was 184.3°C 4. Group five heated chlorine: and the result was -34.04°C Page 127 of 146 Q 34.1 Draw a table to present the results. C3 Teacher's Explanation Table title and column heading Page 128 of 146 Q 34.2 Plot a graph using the results. C3 Teacher's Explanation atomic radius versus the boiling points of the halogens Q 34.3 Using the graph drawn, explain the relationship between the boiling point and atomic C3 radius. Teacher's Explanation The graph between boiling point and atomic radius shows a general trend where the boiling point decreases as the atomic radius increases. This trend suggests that atoms with larger radii tend to have weaker intermolecular forces. As the atomic radius increases, the outermost electrons are farther from the nucleus, weakening the bond to the neighboring atoms and thus lowering the temperature at which the substance transforms from liquid to gas. Page 129 of 146 Q 34.4 Evaluate the validity of the hypothesis based on the outcome of the as presented by C2 the students. Teacher's Explanation The Validity of a Hypothesis Based on Investigation Outcomes In this case, the data supports the hypothesis. The hypothesis is valid because it is supported by data. Q 34.5 Evaluate the validity of the method based on the outcome of the as presented by the C3 students. Teacher's Explanation The method is valid as it enabled the students to collect data that supported the hypothesis and is based on the expected. However, the method should have included at least 5 trials. This would eliminate the chance that it could just be a coincidence. Having 5 trials increases the reliability of the data. Q 34.6 Suggest extensions to the method that would help the students understand the C1 relationship between atomic radius and boiling points of elements in the periodic table. Teacher's Explanation To facilitate a deeper understanding of the relationship between atomic radius and boiling points within the periodic table, the students could investigate the trend of boiling points across a period. Page 130 of 146 Criterion C Page 131 of 146 Q 35.1 A group of students reacted metals with water using the apparatus above to measure C4 the volume of gas produced. Explain improvements to the method to enable the students to measure the volume of the gas accurately. Teacher's Explanation Use a Graduated Cylinder: Instead of the boiling tube, use a graduated cylinder to collect the gas. This will allow for more precise measurement of the gas volume. The graduated markings on the cylinder will provide an accurate reading of the volume in milliliters or cubic centimeters. Ensure an Airtight Seal: Make sure the connection between the test tube and the delivery tube is completely airtight. Any leaks will result in inaccurate gas volume measurements. Use a rubber stopper or other sealant to create an airtight seal. Measure Water Displacement: As the gas collects in the graduated cylinder, it will displace an equal volume of water. By measuring the volume of water displaced, you can determine the volume of gas produced. This method is more accurate than measuring the gas directly. Control Temperature and Pressure: Temperature and pressure can affect the volume of gas produced. Try to maintain a constant temperature throughout the experiment. If possible, conduct the experiment at standard temperature and pressure (STP) conditions for the most accurate results. Repeat Trials: Perform multiple trials of the experiment and take the average gas volume. This will help account for any experimental errors or variations in the reaction. Consistent results across trials will increase confidence in the accuracy of the measurements. Page 132 of 146 Q 35.2 Plot a graph using the data above and the atomic number of the alkali metals. Use C4 the periodic table to find the atomic number of the alkalis. Teacher's Explanation Atomic number versus atomic radius of the alkali metals Q 35.3 Describe and explain the trend in atomic radius down the group. C2 Teacher's Explanation Atomic radius increases down because of the increase in number of shells or energy levels Page 133 of 146 Q 35.4 Suggest the relationship between Atomic radius and reactivity of the Alkali metals C2 down the group Teacher's Explanation As the atomic radius increases down the group, the reactivity also increases. Content type: Video This item includes interactive content. Please refer to the digital version of this assessment to view this item. Q 35.5 Suggest evidence of reactivity of elements with other substances. C1 Teacher's Explanation production of gas formation of precipitate change in colour Page 134 of 146 Q 35.6 Describe the trend in trend in boiling point from fluorine to iodine C1 Teacher's Explanation Increases from fluorine to iodine Q 35.7 Suggest an explanation for the trend of boiling point from fluorine to iodine, C1 Teacher's Explanation As the atomic mass increases from fluorine to iodine, the boiling point increases Page 135 of 146 Criterion Band C Processing and evaluating This section addresses the key concept of relationships and focuses on criterion C (Processing and evaluating). Chemists look for patterns in the periodic table to discover relationships and trends that help them to predict physical and chemical properties. The periodic table, also known as the periodic table of the elements, is a rows and columns arrangement of the chemical elements. Page 136 of 146 Lothar Meyer, a Geman chemist proposed that on arranging elements in the increasing order of their atomic weights, similarities appear in physical and chemical properties at regular intervals. Robert, a student of St. Peter’s school wanted to check for the validity of the hypothesis and compiled a data of Atomic Mass and Atomic Volume of some elements. Element Atomic Mass Atomic Volume ( ) Hydrogen 1 19 Helium 4 40 Lithium 7 18 Beryllium 9 9 Boron 10 8 Carbon 12 4 Nitrogen 14 22 Oxygen 15 21 Fluorine 19 22 Neon 20 22 Sodium 23 29 Magnesium 25 21.5 Aluminium 26 17 Chlorine 35 40 Argon 40 41 Potassium 41 53 Calcium 40.08 41 Iron 56 11 Bromine 80 35 Rubidium 85 60 Strontium 87 40 Page 137 of 146 Q 36.1 Select the most appropriate graph to present the periodic trend of these C1 elements. A Scattered graph B Bubble graph C Bar graph D Line graph Teacher's Explanation D line graph Page 138 of 146 Q 36.2 Use the compiled data of atomic mass and atomic volume and present the data in C 10 a graph. Label the x and y-axis. Teacher's Explanation Graph title - 1 mark Type of graph - 1 mark At least five points plotted correctly - 1 mark Ten points plotted correctly - 2 marks All points plotted correctly- 4 marks. Page 139 of 146 Q 36.3 Using the data in the table, state why alkali metals occupied the peak position. C2 Teacher's Explanation Q 36.4 Suggest one way to improve the validity of the data. C2 Teacher's Explanation pH is a scale used to specify the acidity or basicity of an aqueous solution. Acid solutions are measured to have lower pH values than basic or alkaline solutions. Content type: Video This item includes interactive content. Please refer to the digital version of this assessment to view this item. Page 140 of 146 Q 36.5 State a research question that can be used to study the effect of pH on plants. B1 Teacher's Explanation "How does varying soil pH levels affect the growth and health of plant species X over a period of Y weeks?" How does changing soil pH levels affect the growth and health of plant species X over a period of Y weeks?" a. Q 36.6 Identify the independent variable and describe how you will manipulate it to B3 investigate the ideal pH for plant growth Teacher's Explanation The independent variable in this investigation is the pH level of the soil. To manipulate this variable, you can prepare several soil samples with different pH levels within and outside the ideal range. For example: Sample A: pH 5.5 Sample B: pH 6.0 Sample C: pH 6.5 Sample D: pH 7.0 Sample E: pH 7.5 Sample F: pH 8.0 Ensure to keep other variables such as temperature, light, and water supply constant for all samples. Monitor and measure the plant growth in each sample over a set period, and analyze the data to determine the optimal pH range for plant growth. This manipulation will allow you to observe the effects of different pH levels on plant growth and identify the ideal soil pH conditions. Page 141 of 146 Q 36.7 You are planning to design a method to investigate the pH of the soil of your garden, C5 playground, neighbourhood park, nearest construction site, and nearby farming area. Design a table for recording and processing your data. You should select the number of rows and columns and add labels. The table should include: indication of more than one trial column for independent variable: type of soil column for dependent variable: pH of soil. column for average: pH of soil. Teacher's Explanation Page 142 of 146 Criterion A: Knowing and Understanding Q 37.1 When a substance dissolves, it: A1 A changes into a completely new substance that can disappear in all liquids B breaks apart into smaller particles that are invisible to the naked eye C melts into a new chemical that is invisible D undergoes a chemical change A changes into a completely new substance that can disappear in all liquids B breaks apart into smaller particles that are invisible to the naked eye C melts into a new chemical that is invisible D undergoes a chemical change Q 37.2 Solutions can contain a solid and a liquid. sometimes they can contain two liquids. A1 An example where a solution contains two liquids is: A. a cup of instant coffee B. an ocean of saltwater C. cleaning wet paintbrushes with turpentine or water D. a mixture of cooking oil and milk A a cup of instant coffee B an ocean of saltwater C cleaning wet paintbrushes with turpentine or water D a mixture of cooking oil and milk Page 143 of 146  Heating curves show how the temperature changes as a substance is heated up. Q 37.3 Answer the questions using this heating curve. A3 a. Suggest the boiling point temperature of the substance b. Suggest a letter representing the range where the solid is being warmed c. Suggest the letter that represents the range where the vapor/gas is being warmed Q 37.4 Define atomic number and mass number A1 Q 37.5 A1 Explain why an atom has no charge. Hint. use the charges of subatomic particles in your work Page 144 of 146 Q 37.6 an atom X has the electron arrangement 2.8.1. Describe its position in the periodic A1 table. Q 37.7 Plant leaf pigments can be separated using paper chromatography. The Rf values A2 can then be used to identify the pigments. The Rf value is the ratio of the solute’s distance travelled to the solvent’s distance travelled. Using the diagram below, calculate the Rf value. From the diagram: Distance travelled by the solute = 2.1 cm Distance travelled by the solvent = 2.8 cm Page 145 of 146 Q 37.8 A3 Q 37.9 Analyse and evaluate the effectiveness of using a separating funnel to separate A2 immiscible liquids. Page 146 of 146