The characteristic properties of acids and bases — Paper 3 · IGCSE Science - Combined 0653

5 A student investigates the reaction between dilute sulfuric acid and copper(II) carbonate powder. The apparatus she uses is shown in Fig. 5.1. gas syringe copper(II) carbonate dilute sulfuric acid powder Fig. 5.1 The reaction produces a gas which is collected in the gas syringe. (a) (i) Name the gas and the salt which are produced in this reaction. gas … salt … [2] (ii) Describe the pH change, if any, of the reaction mixture. Name this type of reaction. pH change … reaction type … [2] (b) The student records the volume of gas in the syringe for 10 minutes. Her results are shown in Fig. 5.2. volume of gas 0 1 2 3 4 5 6 7 8 9 10 time / minutes Fig. 5.2 Suggest why the reaction stops at 4 minutes. … … [1] (c) The student repeats the experiment using the same mass of powdered copper(II) carbonate and the same volume of dilute sulfuric acid. Suggest one change that the student can make to decrease the time taken for the reaction to stop. … [1] (d) The formula of sulfuric acid is H2SO4. (i) State the number of different elements and the total number of atoms shown in this formula. number of elements … number of atoms … [2] (ii) Describe a chemical test for sulfate ions and state the positive result. test … … result … [2]

10 marks

Mark scheme: 5(a)(i) carbon dioxide ; copper sulfate ; 2 5(a)(ii) increases ; salt making / neutralisation ; 2 5(b) runs out of / no more (sulfuric) acid / copper carbonate / powder ; 1 5(c) higher temperature / more concentrated (acid) / decrease particle size (of powder) / agitate the flask ; 1 5(d)(i) three / 3 ; seven / 7 ; 2 5(d)(ii) (acidified) barium ions / barium nitrate (soln) ; (result) white ppt / white solid ; 2

This question in 0653/31 May/June 2017

5 (a) Sodium is a Group I metal. An atom of sodium is represented by the symbol 23Na11 (i) State the numbers of electrons, neutrons and protons in this atom. electrons … neutrons … protons … [2] (ii) The electronic structure of a sodium atom is shown in Fig. 5.1a. Fig. 5.1a Fig. 5.1b Complete Fig. 5.1b to show the electronic structure of a sodium ion. [1] (b) Apparatus used in the electrolysis of concentrated aqueous sodium chloride is shown in Fig. 5.2. low voltage d.c. supply – + concentrated aqueous sodium chloride Fig. 5.2 Complete the sentences about the electrolysis of concentrated aqueous sodium chloride. The concentrated aqueous sodium chloride is known as the … . The positive electrode is called the … , and the negative electrode is called the … . At the positive electrode … forms and at the negative electrode … forms. [5] (c) When a teacher adds a piece of sodium to a bowl of water, an exothermic reaction occurs. The teacher uses Universal Indicator to test the solution in the bowl after the reaction. (i) Describe a simple method that the teacher can use to show that the reaction is exothermic. … … … [2] (ii) Describe and explain the effect of the solution in the bowl on the Universal Indicator. effect … explanation … … [2] [Total: 12]

12 marks

Mark scheme: 5(a)(i) (electrons) 11 AND (protons) 11 ; (neutrons) 12 ; 2 5(a)(ii) 2, 8 ; 1 5(b) electrolyte ; anode ; cathode ; chlorine (gas) ; hydrogen (gas) ; 5 5(c)(i) uses a thermometer to measure temperature (before and after) ; temperature should show an increase / idea that heat is given out ; 2 5(c)(ii) (effect) (turns) blue ; (explanation) (forms) (sodium) hydroxide / alkaline (solution) ; 2

This question in 0653/32 Feb/March 2019

5 (a) Calcium hydroxide, a base, is used to control the acidity of soil. (i) Describe the effect of calcium hydroxide on the pH value of acid soil. … [1] (ii) On Fig. 5.1 complete the word equation for the reaction between calcium hydroxide and dilute sulfuric acid. + + water Fig. 5.1 [2] (iii) Describe the test for aqueous calcium ions, Ca2+. State the result that shows the presence of calcium ions. test … result … … [2] (b) A student makes pure crystals of copper sulfate. She adds excess copper oxide powder to dilute sulfuric acid. A blue solution of copper sulfate forms. (i) Explain why excess copper oxide is used. … … [1] (ii) Describe how she separates the unreacted copper oxide powder from the blue solution. … [1] (iii) State two processes that she uses to obtain crystals of copper sulfate from the blue solution. 1. … ………………………………………………………………… … 2. … ………………………………………………………………… … [2] [Total: 9]

9 marks

Mark scheme: 5(a)(i) increases ; 1 5(a)(ii) ;; LHS (1) RHS (1) 2 5(a)(iii) (test) (aqueous) sodium hydroxide ; (result) white precipitate ; 2 5(b)(i) react with all the acid / (make sure) all acid is used up ; 1 5(b)(ii) filter ; 1 Question Answer Marks 5(b)(iii) any two from heat / boil / evaporate ; leave to crystallise / leave to cool ; filter (crystals) ; 2

This question in 0653/33 May/June 2019

5 (a) Some of the apparatus a student uses to investigate the rate of reaction between a piece of zinc and dilute hydrochloric acid is shown in Fig. 5.1. thermometer beaker dilute hydrochloric acid piece of zinc Fig. 5.1 (i) Identify the gas formed in the reaction between zinc and dilute hydrochloric acid. … [1] (ii) Suggest the change in the pH of the mixture in the beaker during this reaction. … [1] (iii) Describe the effect of increasing the temperature on the rate of this reaction. … [1] (iv) The experiment is repeated using the same mass of zinc powder instead of the piece of zinc. Describe how this change affects the rate of the reaction. … [1] (b) Zinc oxide is heated with carbon. Reduction occurs during the reaction. The reaction is endothermic. (i) State what is meant by reduction. … … [1] (ii) State what is meant by endothermic. … … [1] (c) Complete Fig. 5.2 by drawing one straight line from each gas to the test for that gas. gas test use damp red ammonia litmus paper carbon dioxide use a glowing splint oxygen use limewater Fig. 5.2 [2] [Total: 8]

8 marks

Mark scheme: 5(a)(i) hydrogen / H2 ; 1 5(a)(ii) increases ; 1 5(a)(iii) increases ; 1 5(a)(iv) increases ; 1 5(b)(i) loses oxygen ; 1 5(b)(ii) thermal (heat) energy absorbed/taken in ; 1 5(c) three correct lines = 2 marks one or two lines correct = 1 mark 2

This question in 0653/31 Oct/Nov 2019

8 Sodium chloride, NaCl, is an ionic compound. (a) Name one method of obtaining solid sodium chloride from aqueous sodium chloride. … [1] (b) The electronic structures of an atom of sodium, Na, and of an atom of chlorine, Cl, are shown in Fig. 8.1. Na Cl atom atom Fig. 8.1 Complete Fig. 8.2 to show the electronic structure of a sodium ion, Na+, and of a chloride ion, Cl –. Na+ Cl – ion ion Fig. 8.2 [2] (c) Concentrated aqueous sodium chloride is electrolysed using inert electrodes, as shown in Fig. 8.3. low voltage d.c. supply – + concentrated aqueous sodium chloride Fig. 8.3 Complete the word equation for the electrolysis of concentrated aqueous sodium chloride. concentrated aqueous sodium + + sodium hydroxide chloride [2] (d) Suggest the pH of aqueous sodium hydroxide and its effect on the colour of Universal Indicator. pH … colour … [2] (e) State the effect of chlorine gas on damp litmus paper. … [1] [Total: 8]

8 marks

Mark scheme: 8(a) evaporate ; allow distil / crystallise / boil 1 8(b) drawn: Na+ 2, 8 ; Cl– 2, 8, 8 ; 2 8(c) (either order) concentrated aqueous sodium chloride  sodium hydroxide + hydrogen ; + chlorine ; 2 8(d) pH > 7 to 14 ; colour blue-green / blue / purple ; 2 8(e) (blue / purple to) white / bleached ; 1

This question in 0653/32 Feb/March 2020

8 (a) Sodium chloride is made when aqueous sodium hydroxide is mixed with dilute hydrochloric acid. State what happens to the pH of the mixture as the aqueous sodium hydroxide is added to the dilute hydrochloric acid. … [1] (b) Sodium is in Group I of the Periodic Table, and chlorine is in Group VII. (i) Describe the change in character of elements across a period in the Periodic Table from left to right. … … [1] (ii) Describe the trend in reactivity of Group I metals from lithium to potassium. … … [1] (iii) Describe the trend in physical state of Group VII elements from fluorine to iodine. … … [1] (c) Aqueous bromine reacts with alkenes. (i) State the colour change that occurs during this reaction. … [1] (ii) Name the reaction that produces alkenes from larger alkane molecules. … [1] [Total: 6]

6 marks

Mark scheme: 8(a) 1 8(b)(i) metal(lic) to non-metal(lic) ; 1 8(b)(ii) increases ; 1 8(b)(iii) gas to (liquid to) solid / increasing, melting / boiling point ; 1 8(c)(i) decolourises / brown disappears / brown to colourless ; 1 8(c)(ii) (catalytic) cracking ; 1

This question in 0653/31 Oct/Nov 2020

8 (a) An atom of lead is represented by the symbol shown. 207 Pb 82 (i) Deduce the number of electrons and number of neutrons in this atom. electrons … neutrons … [2] (ii) The proton number (atomic number) of lead is 82. Define the term proton number. … … [1] (iii) State the charges of protons, neutrons and electrons. protons … neutrons … electrons … [1] (b) Lead is extracted from molten lead(II) bromide using the apparatus shown in Fig. 8.1. low voltage d.c. supply – + molten lead(II) bromide Fig. 8.1 (i) Name the process shown in Fig. 8.1. … [1] (ii) State the name of the electrode at which lead forms. … [1] (c) Lead is extracted from lead(II) oxide, PbO, by heating with carbon. Carbon dioxide is also made in this endothermic reaction. (i) Describe what is meant by an endothermic reaction. … … [1] (ii) Complete the word equation for this reaction. + lead + [1] (iii) Circle the word to show whether lead(II) oxide is oxidised or reduced in this reaction. Explain your answer. oxidised reduced explanation … … (d) A teacher has a different compound of lead. When this compound of lead reacts with dilute hydrochloric acid, carbon dioxide is formed. Suggest the name of this compound of lead. … [1] [Total: 10]

10 marks

Mark scheme: 8(a)(i) (electrons) 82 ; (neutrons) 125 ; 2 8(a)(ii) the number of protons in the nucleus of an atom ; 1 8(a)(iii) (protons) +1 (neutrons) no charge (electrons) -1 ; all three needed for one mark 1 Question Answer Marks 8(b)(i) electrolysis ; 1 8(b)(ii) cathode ; 1 8(c)(i) takes in, heat / energy ; 1 8(c)(ii) ; 1 8(c)(iii) reduced (circled) AND (explanation) loses oxygen ; 1 8(d) lead carbonate / PbCO3 ; 1

This question in 0653/32 Feb/March 2021

2 (a) Fig. 2.1 shows part of Group I of the Periodic Table. 3 Li lithium 7 11 Na sodium 23 19 K potassium 39 Fig. 2.1 (i) State the trend in the reactivity of the elements going down Group I. … [1] (ii) Explain why lithium does not react with helium, a Group VIII element. … … [1] (iii) Lithium is a solid and helium is a gas. Describe two differences between the structures of a solid and a gas. 1 … … 2 … … [2] (b) A piece of sodium is added to water, as shown in Fig. 2.2. sodium water Fig. 2.2 The sodium reacts with water. The reaction is exothermic. (i) State one other observation that is seen when sodium reacts with water. … [1] (ii) Complete the word equation for the reaction of sodium with water. sodium + water + [2] (c) X is a compound that reacts with dilute hydrochloric acid to form sodium chloride and water. Suggest the identity of X. … [1] (d) Concentrated aqueous sodium chloride is broken down by electrolysis. (i) State the type of chemical bond in sodium chloride. … [1] (ii) Identify the product that forms at the anode (positive electrode). … [1] [Total: 10]

10 marks

Mark scheme: 2(a)(i) increasing / more reactive / faster reaction ; 1 2(a)(ii) helium / He is, unreactive / inert ; 1 2(a)(iii) any two from: (solid/lithium) particles close(r) (together) ORA ; (solid/lithium) particles regular arrangement ORA ; (solid/lithium) particles vibrate / not free-moving ORA ; 2 Question Answer Marks 2(b)(i) fizzes / bubbles OR gets smaller / disappears OR moves around ; 1 2(b)(ii) sodium + water → sodium hydroxide + hydrogen in either order sodium hydroxide ; hydrogen ; 2 2(c) sodium hydroxide / NaOH OR sodium carbonate / Na2CO3 ; 1 2(d)(i) ionic ; 1 2(d)(ii) chlorine / Cl2 ; 1

This question in 0653/31 May/June 2021

5 Magnesium sulfate is produced by reacting excess magnesium oxide with dilute sulfuric acid. (a) Complete the word equation for this reaction. magnesium + + sulfate [2] (b) A coloured aqueous solution is used to measure the pH of dilute sulfuric acid. (i) State the name of the coloured aqueous solution that is used to measure the pH of acids and alkalis. … [1] (ii) Suggest the pH value of dilute sulfuric acid. … [1] (c) Complete the sentences about the preparation of salt crystals. Use words from the list. Each word may be used once, more than once or not at all. acid filtering heating magnesium distillation magnesium sulfate shaking solid Excess magnesium oxide is added to dilute sulfuric acid and stirred until no more … dissolves. Pure aqueous magnesium sulfate is separated by … . Some water is removed by gentle … . The solution is then left to form pure dry crystals of the salt called … . [4] (d) Magnesium sulfate contains magnesium ions, Mg2+. Describe how magnesium ions are formed from magnesium atoms. … [1] (e) Aqueous magnesium sulfate is broken down by an electric current. State the name of this process. … [1] [Total: 10]

10 marks

Mark scheme: 5(a) magnesium oxide + sulfuric acid  magnesium sulfate + water ;; LHS (1) RHS (1) 5(b)(i) universal indicator ; 1 5(b)(ii) 1 – 6 ; 1 5(c) solid ; filtering / filtration ; heating ; magnesium sulfate ; 4 5(d) loss of electrons ; 1 Question Answer Marks 5(e) electrolysis ; 1

This question in 0653/33 May/June 2023

2 A student dissolves sodium carbonate, Na2CO3, in water to form aqueous sodium carbonate. (a) (i) State a chemical test for water and the observation for a positive result. test … observation … [2] (ii) Complete Fig. 2.1 to show the dot-and-cross diagram of a molecule of water. Show all of the outer shell electrons. H O H Fig. 2.1 [2] (b) The student measures the boiling point of the aqueous sodium carbonate. (i) State the piece of apparatus used to measure the temperature of the boiling point of the aqueous sodium carbonate. … [1] (ii) State whether boiling is a chemical or a physical change. Give a reason for your answer. change … reason … … [1] (iii) During boiling, thermal energy (heat) is taken in. State the name for the type of process that takes in thermal energy. … [1] (c) The student adds dilute hydrochloric acid to a sample of aqueous sodium carbonate. Complete the word equation for the reaction. sodium hydrochloric + + +carbonate acid [2] [Total: 9]

9 marks

Mark scheme: 2(a)(i) test (anhydrous) copper sulfate ; 2 observation (white to) blue ; OR test (anhydrous) cobalt chloride ; observation (blue to) pink ; 2(a)(ii) one bond pair between each H atom and O atom ; 2 two lone pairs on O atom and all else correct ; 2(b)(i) thermometer ; 1 2(b)(ii) change physical AND 1 explanation no new substance is made ; 2(b)(iii) endothermic ; 1 2(c) 2 sodium chloride correct / carbon dioxide and water correct ; all three correct ;

This question in 0653/31 Oct/Nov 2023

5 (a) Fig. 5.1 is a pie chart showing the composition of clean air. Fig. 5.1 Identify the gases in clean air by completing the key for the pie chart shown in Fig. 5.1. Key … … … and … and … [3] (b) Carbon monoxide and the oxides of nitrogen are common pollutants in air. State one adverse effect that each of these air pollutants causes. carbon monoxide … … oxides of nitrogen … … [2] (c) Carbon dioxide is a gas. (i) Carbon dioxide forms during the thermal decomposition of calcium carbonate. Calcium oxide is the other product. Write the word equation for this reaction in the boxes. + [1] (ii) Calcium carbonate reacts with dilute hydrochloric acid to form carbon dioxide. Suggest a value for the pH of dilute hydrochloric acid. pH = … [1] (d) Hydrogen chloride, HCl , is a covalent molecule. Complete Fig. 5.2 to show the dot-and-cross diagram for a molecule of hydrogen chloride. Show only the electrons in the outer shells. H Cl Fig. 5.2 [2] [Total: 9]

9 marks

Mark scheme: 5(a) (grey shading) nitrogen 3 (dots shading) oxygen (white shading) noble gases / named noble gas (white shading) water vapour (white shading) carbon dioxide ;;; 5 correct = [3] 3–4 correct = [2] 1–2 correct = [1] 5(b) carbon monoxide: 2 headaches / tiredness / confusion / toxic ; oxides of nitrogen: acid rain / damages buildings ; 5(c)(i) calcium carbonate → calcium oxide + carbon dioxide ; 1 5(c)(ii) 1–4 ; 1 5(d) shared pair of electrons ; 2 3 lone pairs in Cl and no other electrons in H ;

This question in 0653/32 Feb/March 2024

2 A student investigates the reaction of magnesium with excess dilute hydrochloric acid using the apparatus shown in Fig. 2.1. excess dilute hydrochloric acid magnesium Fig. 2.1 The equation for the reaction is shown. Mg + 2HCl MgCl2 + H2 (a) The student repeats the experiment at the same temperature, using the same volume of acid with a lower concentration. Describe the effect of this change on the rate of the reaction. … [1] (b) Describe the effect of dilute hydrochloric acid on litmus paper. … [1] (c) Describe a chemical test for hydrogen gas. State the observation for a positive result. test … observation … … [2] (d) One alloy contains copper and magnesium. (i) State what is meant by an alloy. … … [1] (ii) Copper is extracted from copper oxide by heating with carbon. Magnesium cannot be extracted from magnesium oxide by heating with carbon. Explain these observations. copper … … magnesium … … [2] [Total: 7]

7 marks

Mark scheme: 2(a) (rate of reaction) decreases / slows down ; 1 2(b) (turns blue litmus paper) red ; 1 2(c) (test) lighted splint ; (observation) ‘pops’ ; 2 2(d)(i) a mixture of a metal with another element(s) ; 1 2(d)(ii) (copper) is less reactive than carbon ORA ; (magnesium) is more reactive than carbon ORA ; 2

This question in 0653/32 May/June 2024

5 Dilute sulfuric acid is used in an electrolysis experiment. (a) Universal indicator is used to measure the pH of the dilute sulfuric acid. Describe how to use universal indicator to measure pH. … … … [2] (b) Fig. 5.1 shows the electrolysis. dilute sulfuric acid positive electrode negative electrode power supply Fig. 5.1 (i) Identify the gas formed at each electrode. negative electrode … positive electrode … [2] (ii) State the name of the positive electrode. … [1] (iii) Identify the electrolyte in this electrolysis. … [1] (c) The volume of gas formed at each electrode is measured every 30 s for 2 min. The results are shown in Table 5.1. Table 5.1 volume of gas at the volume of gas at the time negative electrode positive electrode / s / cm3 / cm3 0 0 0 30 18 9 60 36 18 90 54 27 120 36 (i) Use Table 5.1 to predict the volume of gas given off at the negative electrode at 120 s. volume = … cm3 [1] (ii) Use Table 5.1 to calculate the volume of gas formed per second at the positive electrode. volume = … cm3 / s [1] [Total: 8]

8 marks

Mark scheme: 5(a) (add UI to the acid and) look at the colour / state acid gives red colour ; 2 compare to a (pH number) chart ; 5(b)(i) negative electrode: hydrogen ; 2 positive electrode: oxygen ; 5(b)(ii) anode ; 1 5(b)(iii) (dilute) sulfuric acid ; 1 5(c)(i) 72 (cm3) ; 1 5(c)(ii) 0.3 (cm3 / s) ; 1

This question in 0653/33 May/June 2025