Elements, compounds and mixtures — Paper 3 · IGCSE Sciences - Co-ordinated (Double) 0654

5 Ionic compounds contain ions. Covalent compounds are made of molecules. Mixtures contain two or more compounds or elements. (a) (i) Complete Table 5.1 by writing a tick (3) in the column that describes each substance. Table 5.1 covalent substance element ionic compound mixture compound air bromine carbon dioxide iron oxide [3] (ii) Glucose has the chemical formula C6H12O6. Describe what this chemical formula shows about the elements in one molecule of glucose. … … … [2] (b) Fig. 5.1 shows processes, P and Q, that are used to extract metallic elements from metal compounds. P Q copper chloride solution gas inert inert anode cathode mixture of lead oxide and carbon switch d.c. power supply heat (i) Name process P. … [1] (ii) Describe what is observed at the anode and at the cathode in process P when the switch in Fig. 5.1 is closed. at the anode … at the cathode … [2] (iii) In process Q, a redox reaction occurs that produces lead and a gas. Complete the word equation for the reaction that occurs in process Q. + lead + [2] (iv) State and explain which of the reacting substances is reduced during the reaction in process Q. substance … explanation … … [1]

11 marks

Mark scheme: 5(a)(i) substance element ionic compound covalent compound mixture air 9 bromine 9 carbon dioxide 9 iron oxide 9 1 or 2 ticks correct ; 3 ticks correct ; 4 ticks correct ; 3 5(a)(ii) contains carbon hydrogen and oxygen ; shows 6 × C 12 × H 6 × O atoms ; 2 5(b)(i) electrolysis ; 1 Question Answer Marks 5(b)(ii) anode – bubbles / gas released ; cathode – colour change / coloured layer forms / pink / orange layer forms ; 2 5(b)(iii) lead oxide + carbon → (lead) + carbon dioxide / monoxide LHS correct ; RHS correct ; 2 5(b)(iv) (lead oxide) oxygen removed ; 1

This question in 0654/32 Oct/Nov 2017

2 Calcium carbonate, CaCO3, is the main compound in limestone. (a) (i) State the number of different elements shown in the formula of calcium carbonate. … [1] (ii) Calcium carbonate reacts with hydrochloric acid to produce calcium chloride and two other products. Complete the word equation for this reaction. hydrochloric calcium calcium + + + acid carbonate chloride [2] (iii) Describe one observation during the reaction in (a)(ii) that shows a chemical reaction is taking place. … [1] (iv) Describe a chemical test, and its result, for chloride (Cl −) ions. test … result … [2] (b) A student heats 10.0 g of limestone strongly for several minutes. The limestone changes into a white solid M. The mass of solid M is 5.6 g. (i) State the type of chemical reaction that occurs when limestone is heated strongly. … [1] (ii) Explain why the mass of solid M is lower than that of the original piece of limestone. … … [1] (iii) State the name of solid M. … [1] (c) Describe why limestone is sometimes used to treat soil. … … [1]

10 marks

Mark scheme: 2(a)(i) 3 ; 1 2(a)(ii) carbon dioxide ; water ; 2 2(a)(iii) effervescence ; temperature increase ; AVP max 1 2(a)(iv) (dilute nitric acid, then) silver nitrate ; white ppt. ; 2 2(b)(i) (thermal) decomposition ; 1 2(b)(ii) gas / carbon dioxide released / given off ; 1 2(b)(iii) calcium oxide / quicklime / lime ; 1 2(c) reference to the reduction of acidity ; 1

This question in 0654/31 Oct/Nov 2018

2 Air is a mixture of gases. Most of the air is made up of nitrogen and oxygen. (a) Fig. 2.1 shows pie charts representing two mixtures of gases J and K. These mixtures are different from clean air. other gases other gases nitrogen oxygen nitrogen oxygen mixture J mixture K Fig. 2.1 Describe one difference between clean air and: mixture J … … mixture K. … … [2] (b) The air in cities contains pollutants including carbon monoxide. (i) Describe how carbon monoxide is formed. … … [1] (ii) State why carbon monoxide is harmful to health. … … [1] (iii) Clean air contains small amounts of elements found in Group VIII of the Periodic Table. Identify the Group VIII element in the third period of the Periodic Table. … [1] (iv) Explain why clean air containing this Group VIII element is not harmful to humans. … … [1] (c) Fig. 2.2 shows diagrams of some of the molecules in air. O H H N N O C O O O Fig. 2.2 (i) On Fig. 2.2, draw a label line to a molecule of an element and label it E. Explain your answer. … … [1] (ii) On Fig. 2.2, draw a label line to the molecule of water and label it W. Explain your answer. … … [1] (iii) Describe a chemical test and its result to show that the air contains water. test … result … [2]

10 marks

Mark scheme: 2(a) J too great a proportion of other gases / too little oxygen; K nitrogen and oxygen the wrong way round; 2 2(b)(i) incomplete combustion of hydrocarbons / fuel; 1 2(b)(ii) toxic; 1 2(b)(iii) argon / Ar; 1 2(b)(iv) it is inert / does not react in the body; 1 2(c)(i) (label to either N2 or O2) only one type of atom; 1 2(c)(ii) (label to H2O) water molecules contain two hydrogen atoms and one oxygen atom; 1 2(c)(ii) cobalt chloride (paper); turns from blue to pink; 2

This question in 0654/32 Oct/Nov 2018

2 Fig. 2.1 shows the chemical symbols of five elements in Period 4 of the Periodic Table. A copy of the whole Periodic Table is on page 36. 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Mn Co Br Kr Fig. 2.1 (a) (i) Explain what the numbers 19 to 36 represent for the elements in Period 4 from K to Kr. … … [1] (ii) Using only the symbols shown in Fig. 2.1, identify: a metallic element … a non-metallic element … a transition metal … a halogen … the least reactive element in the period … an element that reacts violently with water. … [3] (b) An atom of phosphorus contains 15 electrons. Complete Fig. 2.2 to show the number of electrons in each shell of a phosphorus atom. One electron in each shell has been drawn for you. electron x x x Fig. 2.2 [2] (c) The elements hydrogen and oxygen combine to form water, H2O. Fig. 2.3 shows molecules in a mixture of hydrogen and oxygen. Fig. 2.4 shows molecules in water vapour. Fig. 2.3 Fig. 2.4 (i) State the formula of an oxygen molecule. … [1] (ii) Use Fig. 2.3 and Fig. 2.4 to describe one difference between a mixture of two elements and a compound of two elements. … … … … [2] [Total: 9]

9 marks

Mark scheme: 2(a)(i) this is the proton number / atomic number – the number of protons (in an atom) ; 1 2(a)(ii) K / Mn / Co Br / Kr Mn / Co Br Kr K 2 or 3 correct ; 4 or 5 correct ; 6 correct ; 3 2(b) inner shells 2.8 ; outer shell 5 ; 2 2(c)(i) O2 ; 1 2(c)(ii) mixture – different atoms not bonded to each other ; compound – different atoms bonded together ; or mixture – idea that relative amounts of different atoms not fixed ; compound – has a formula / fixed ratio of atoms ; 2

This question in 0654/32 May/June 2019

2 Fig. 2.1 shows the chemical symbols of five elements in Period 4 of the Periodic Table. A copy of the whole Periodic Table is on page 36. 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Mn Co Br Kr Fig. 2.1 (a) (i) Explain what the numbers 19 to 36 represent for the elements in Period 4 from K to Kr. … … [1] (ii) Using only the symbols shown in Fig. 2.1, identify: a metallic element … a non-metallic element … a transition metal … a halogen … the least reactive element in the period … an element that reacts violently with water. … [3] (b) An atom of phosphorus contains 15 electrons. Complete Fig. 2.2 to show the number of electrons in each shell of a phosphorus atom. One electron in each shell has been drawn for you. electron x x x Fig. 2.2 [2] (c) The elements hydrogen and oxygen combine to form water, H2O. Fig. 2.3 shows molecules in a mixture of hydrogen and oxygen. Fig. 2.4 shows molecules in water vapour. Fig. 2.3 Fig. 2.4 (i) State the formula of an oxygen molecule. … [1] (ii) Use Fig. 2.3 and Fig. 2.4 to describe one difference between a mixture of two elements and a compound of two elements. … … … … [2] [Total: 9]

9 marks

Mark scheme: 2(a)(i) this is the proton number / atomic number – the number of protons (in an atom) ; 1 2(a)(ii) K / Mn / Co Br / Kr Mn / Co Br Kr K 2 or 3 correct ; 4 or 5 correct ; 6 correct ; 3 2(b) inner shells 2.8 ; outer shell 5 ; 2 2(c)(i) O2 ; 1 2(c)(ii) mixture – different atoms not bonded to each other ; compound – different atoms bonded together ; or mixture – idea that relative amounts of different atoms not fixed ; compound – has a formula / fixed ratio of atoms ; 2

This question in 0654/33 May/June 2019

5 (a) Lithium, sodium and potassium are alkali metal elements in the Periodic Table. Table 5.1 shows the melting points of lithium, sodium and potassium. Table 5.1 metal melting point / °C lithium 181 sodium 98 potassium 64 State the trend in the melting points of the elements from lithium to potassium. … [1] (b) An atom of sodium has a nucleon number (mass number) of 23 and a proton number (atomic number) of 11. Fig. 5.1 shows the structure of an atom of sodium. electron … … Fig. 5.1 (i) On Fig. 5.1, complete the labels for the sodium atom. [2] (ii) State the electronic structure for this sodium atom. … [1] (c) Sodium and chlorine react to form sodium chloride. Fig. 5.2 shows the electronic structure of a sodium atom and a chlorine atom. Na Cl sodium atom chlorine atom Fig. 5.2 Draw diagrams to show the electronic structures of a sodium ion and of a chloride ion when sodium reacts with chlorine. Include the charge for each ion. sodium ion chloride ion [3] (d) Sodium and chlorine are elements. Sodium chloride is a compound. Describe the difference between an element and a compound. … … … [2] [Total: 9]

9 marks

Mark scheme: 5(a) melting point decreases (down group) ; 1 5(b)(i) proton; neutron; 2 Question Answer Marks 5(b)(ii) 2.8.1; 1 5(c) sodium ion 2.8 ; chloride ion 2.8.8 ; sodium has positive charge and chloride has negative charge indicated; 3 5(d) an element contains only one type of atom; a compound contains two or more elements (chemically) combined / bonded; 2

This question in 0654/32 Feb/March 2021

8 (a) Fig. 8.1 shows three molecules A, B and C. H H H H H H C C O H H C H C C H H H H H A B C Fig. 8.1 State the formula of the substance that reacts with molecule C to make molecule A. … [1] (b) Molecule B, CH4, is methane which is a compound. Methane contains the elements carbon and hydrogen. Use this information to explain the difference between an element and a compound. … … … [2] (c) State the two products made when methane undergoes complete combustion in oxygen. 1 … 2 … [2] (d) The combustion of methane is an exothermic reaction. State what is meant by exothermic. … … [1] (e) An atom of carbon has a nucleon number (mass number) of 12 and a proton number (atomic number) of 6. An atom of hydrogen has a nucleon number (mass number) of 1 and a proton number (atomic number) of 1. (i) State the number of electrons in an atom of carbon and in an atom of hydrogen. carbon … hydrogen … [1] (ii) State the number of neutrons in this atom of hydrogen. … [1] (f) Complete the dot‑and‑cross diagram in Fig. 8.2 to show the bonding in a methane, CH4, molecule. H H C H H Fig. 8.2 [2] [Total: 10]

10 marks

Mark scheme: 8(a) H2O ; 1 8(b) an element (e.g. carbon) contains only one type of atom ; a compound (e.g. methane) contains two or more elements / different atoms chemically combined ; 2 8(c) carbon dioxide ; water ; 2 8(d) releases thermal energy ; 1 8(e)(i) carbon 6 and hydrogen 1 ; 1 8(e)(ii) zero ; 1 Question Answer Marks 8(f) one shared pair seen ; all correct ;; 2

This question in 0654/31 May/June 2021

8 (a) Table 8.1 shows a list of covalently bonded molecules. Table 8.1 molecule Cl2 CO2 H2 HCl H2O NH3 (i) Identify two molecules from Table 8.1 that are elements. … and … [1] (ii) Identify one molecule from Table 8.1 that is diatomic. … [1] (iii) Identify one molecule from Table 8.1 which is a greenhouse gas. … [1] (b) (i) State the names of the two elements present in a molecule of ammonia, NH3. … and … [1] (ii) Determine the total number of atoms in a molecule of ammonia, NH3. … [1] (c) Water, H2O, is a solvent. State the meaning of the term solvent. … … [1] (d) Dilute hydrochloric acid reacts with calcium carbonate to produce carbon dioxide, water and a solution of a salt. (i) State which salt is produced. … [1] (ii) Suggest a method of obtaining a sample of the dry salt from this salt solution. … [1] (iii) When calcium carbonate and dilute hydrochloric acid react, the rate of reaction is slow. Suggest two ways of increasing the rate of reaction. 1 … 2 … [2] [Total: 10]

10 marks

Mark scheme: 8(a)(i) 8(a)(ii) HCl, / Cl2 / H2; 1 8(a)(iii) CO2 ; 1 8(b)(i) nitrogen and hydrogen; 1 8(b)(ii) 4; 1 8(c) a (liquid) in which other substances dissolve; 1 8(d)(i) calcium chloride; 1 8(d)(ii) evaporation; 1 8(d)(iii) increase temperature; increase surface area / decrease particle size; increase concentration of acid; 2

This question in 0654/32 Feb/March 2022

11 (a) Fig. 11.1 shows part of Group I of the Periodic Table. 3 Li lithium 7 11 Na sodium 23 19 K potassium 39 37 Rb rubidium 85 Fig. 11.1 (i) State the electronic structure of a potassium atom. … [1] (ii) Describe how the electronic structure of potassium is related to its group number. … … [1] (iii) The proton number of a potassium atom is 19. The nucleon number of this potassium atom is 39. State the numbers of electrons and neutrons in this potassium atom. electrons … neutrons … [2] (iv) Complete Table 11.1 to show the charges and approximate relative masses of an electron and a neutron. Table 11.1 particle charge relative mass proton +1 1 electron … … neutron … … [2] (b) Potassium, K, is an element. Potassium hydroxide, KOH, is a compound. Explain the difference between an element and a compound. element … … compound … … [2] (c) Balance the symbol equation for the reaction between potassium and water. … K + … H2O … KOH + H2 [2] [Total: 10]

10 marks

Mark scheme: 11(a)(i) 2.8.8.1; 1 11(a)(ii) number of outer shell electrons is the same as group number; 1 11(a)(iii) electrons = 19; neutrons = 20; 2 11(a)(iv) particle charge relative mass proton + 1 1 electron –1 0 or 1 / 2000 neutron 0 1 2 11(b) element – contains only one type of atom; compound –contains two or more elements chemically combined ; 2 11(c) 2K + 2H2O  2KOH + H2 LHS 1 ; RHS 1; 2

This question in 0654/31 May/June 2022

11 Fig. 11.1 shows the structures of four molecules, P, Q, R and S. H H H H H H C C C H H C C O H H H H H H P Q H H H H C H C C H H H R S Fig. 11.1 (a) (i) State which of the molecules P, Q, R or S is an alkene. … [1] (ii) State which of the molecules P, Q, R or S is ethanol. … [1] (iii) State which of the molecules P, Q, R or S is the main constituent of natural gas. … [1] (iv) State which two of the molecules P, Q, R and S are saturated hydrocarbons. … and … [1] (b) Carbon dioxide is made during the complete combustion of substance R. State the name of the other product made in this reaction. … [1] (c) Molecule S is a compound made from the two elements carbon and hydrogen. State what is meant by a compound. … … [1] (d) Deduce the formula of molecule P. … [1] (e) Fig. 11.2 shows an incomplete dot-and-cross diagram for molecule R. Complete Fig. 11.2. Show the outer-shell electrons only. H H C H H Fig. 11.2 [2] [Total: 9]

9 marks

Mark scheme: 11(a)(i) S; 1 11(a)(ii) Q; 1 11(a)(iii) R; 1 Question Answer Marks 11(a)(iv) P and R ; 1 11(b) water ; 1 11(c) a compound contains two or more elements chemically combined; 1 11(d) C3H8 ; 1 11(e) one bonding pairs; all else correct ; 2

This question in 0654/32 May/June 2022

11 Fig. 11.1 shows the structures of four molecules, P, Q, R and S. H H H H H H C C C H H C C O H H H H H H P Q H H H H C H C C H H H R S Fig. 11.1 (a) (i) State which of the molecules P, Q, R or S is an alkene. … [1] (ii) State which of the molecules P, Q, R or S is ethanol. … [1] (iii) State which of the molecules P, Q, R or S is the main constituent of natural gas. … [1] (iv) State which two of the molecules P, Q, R and S are saturated hydrocarbons. … and … [1] (b) Carbon dioxide is made during the complete combustion of substance R. State the name of the other product made in this reaction. … [1] (c) Molecule S is a compound made from the two elements carbon and hydrogen. State what is meant by a compound. … … [1] (d) Deduce the formula of molecule P. … [1] (e) Fig. 11.2 shows an incomplete dot-and-cross diagram for molecule R. Complete Fig. 11.2. Show the outer-shell electrons only. H H C H H Fig. 11.2 [2] [Total: 9]

9 marks

Mark scheme: 11(a)(i) S; 1 11(a)(ii) Q; 1 11(a)(iii) R; 1 Question Answer Marks 11(a)(iv) P and R ; 1 11(b) water ; 1 11(c) a compound contains two or more elements chemically combined; 1 11(d) C3H8 ; 1 11(e) one bonding pairs; all else correct ; 2

This question in 0654/33 May/June 2022

11 (a) Sodium and chlorine are elements. Sodium chloride is a compound. Describe what is meant by an element and a compound. element … … compound … … [2] (b) Sodium reacts with chlorine to make sodium chloride. Balance the symbol equation for this reaction. … Na + Cl2 … NaCl [1] (c) When sodium reacts with chlorine, sodium atoms become sodium ions and chlorine atoms become chloride ions. The electron configuration of a sodium atom is 2.8.1. The electron configuration of a chlorine atom is 2.8.7. State the electron configuration of a sodium ion and a chloride ion. sodium ion … chloride ion … [2] (d) Describe the difference in the solubility in water of an ionic compound compared with a covalent compound. … … [1] (e) Sodium chloride contains chloride ions. Describe the test for chloride ions and state the observation for a positive result. test … observation … [2] (f) Fig. 11.1 shows the electrolysis of concentrated aqueous sodium chloride. low voltage d.c. supply – + concentrated aqueous sodium chloride Fig. 11.1 Complete the sentences about the electrolysis of concentrated aqueous sodium chloride. Electrolysis is defined as the breakdown of an ionic compound when … or in aqueous solution by the passage of … The gas released at the negative electrode is … and the gas released at the positive electrode is … . [4] [Total: 12]

12 marks

Mark scheme: 11(a) element – contains only one type of atom ; 2 compound – contains two or more elements (chemically combined) ; 11(b) 2Na + Cl2 → 2NaCl ; 1 11(c) sodium ion 2.8 ; 2 chloride ion 2.8.8 ; 11(d) solubility of ionic compound is greater ; 1 11(e) add acidified aqueous silver nitrate ; 2 white precipitate ; 11(f) molten ; 4 electricity ; hydrogen ; chlorine ;

This question in 0654/31 Oct/Nov 2022

11 (a) (i) An atom of calcium has 20 protons and 20 neutrons. State the number of electrons in this calcium atom. … [1] (ii) State the number of electrons in one calcium ion, Ca2+. … [1] (b) Limestone (calcium carbonate) and lime (calcium oxide) are both calcium compounds. Fig. 11.1 shows a limekiln in which calcium carbonate thermally decomposes to make calcium oxide and carbon dioxide. waste gases containing carbon dioxide calcium carbonate thermally decomposing carbon burning to provide thermal energy air Fig. 11.1 (i) Write the word equation for the thermal decomposition of calcium carbonate. … [1] (ii) The mass of calcium oxide made in this reaction is always less than the mass of calcium carbonate used. Suggest why. … … [1] (iii) The decomposition of calcium carbonate to calcium oxide is an endothermic reaction. State the meaning of the term endothermic. … … [1] (iv) One use for limestone is in the production of lime. State one other use of limestone. … … [1] (v) Suggest why the calcium carbonate is broken into small pieces before being thermally decomposed. … … … [2] (c) Calcium carbonate has the formula CaCO3. (i) State the number of different elements shown in this formula. … [1] (ii) State the total number of atoms shown in this formula. … [1] [Total: 10]

10 marks

Mark scheme: 11(a)(i) 20 (electrons) ; 1 11(a)(ii) 18 (electrons) ; 1 11(b)(i) calcium carbonate  calcium oxide  carbon dioxide ; 1 11(b)(ii) carbon dioxide released ; 1 11(b)(iii) (thermal) energy taken in ; 1 11(b)(iv) neutralising acidified soil ; 1 Question Answer Marks 11(b)(v) to increase surface area ; so that reaction is faster ; 2 11(c)(i) three ; 1 11(c)(ii) five ; 1

This question in 0654/32 May/June 2023

11 (a) (i) An atom of calcium has 20 protons and 20 neutrons. State the number of electrons in this calcium atom. … [1] (ii) State the number of electrons in one calcium ion, Ca2+. … [1] (b) Limestone (calcium carbonate) and lime (calcium oxide) are both calcium compounds. Fig. 11.1 shows a limekiln in which calcium carbonate thermally decomposes to make calcium oxide and carbon dioxide. waste gases containing carbon dioxide calcium carbonate thermally decomposing carbon burning to provide thermal energy air Fig. 11.1 (i) Write the word equation for the thermal decomposition of calcium carbonate. … [1] (ii) The mass of calcium oxide made in this reaction is always less than the mass of calcium carbonate used. Suggest why. … … [1] (iii) The decomposition of calcium carbonate to calcium oxide is an endothermic reaction. State the meaning of the term endothermic. … … [1] (iv) One use for limestone is in the production of lime. State one other use of limestone. … … [1] (v) Suggest why the calcium carbonate is broken into small pieces before being thermally decomposed. … … … [2] (c) Calcium carbonate has the formula CaCO3. (i) State the number of different elements shown in this formula. … [1] (ii) State the total number of atoms shown in this formula. … [1] [Total: 10]

10 marks

Mark scheme: 11(a)(i) 20 (electrons) ; 1 11(a)(ii) 18 (electrons) ; 1 11(b)(i) calcium carbonate  calcium oxide  carbon dioxide ; 1 11(b)(ii) carbon dioxide released ; 1 11(b)(iii) (thermal) energy taken in ; 1 11(b)(iv) neutralising acidified soil ; 1 Question Answer Marks 11(b)(v) to increase surface area ; so that reaction is faster ; 2 11(c)(i) three ; 1 11(c)(ii) five ; 1

This question in 0654/33 May/June 2023

8 (a) Table 8.1 gives statements about molecules in solids and gases. Put a tick (✓) next to each statement to show if it refers to a solid or to a gas. Table 8.1 statement solid gas molecules are closely packed molecules are free to move around molecules are widely separated molecules vibrate about fixed positions [2] (b) Use the list of substances to answer the following questions. Each substance may be used once, more than once or not at all. carbon chlorine copper ethanol oxygen water (i) Identify one substance which is a compound. … [1] (ii) Identify two substances which are solvents. 1 … 2 … [2] (iii) Identify one substance which is a transition element. … [1] (iv) Identify one substance which is a halogen. … [1] (v) Identify one substance which consists of diatomic molecules. … [1] [Total: 8]

8 marks

Mark scheme: 8(a) 2 statement solid gas molecules are closely packed ✓ molecules are free to move around ✓ molecules are widely separated ✓ molecules vibrate about a fixed position ✓ 2 or 3 correct ; 4 correct ; 8(b)(i) ethanol / water ; 1 8(b)(ii) ethanol ; 2 water ; 8(b)(iii) copper ; 1 8(b)(iv) chlorine ; 1 8(b)(v) chlorine / oxygen ; 1

This question in 0654/31 Oct/Nov 2023

5 (a) Ice is a solid. Water is a liquid. Steam is a gas. Fig. 5.1 shows the different arrangement of the particles in ice, water and steam. A B C Fig. 5.1 State and explain which diagram, A, B or C, shows the arrangement of particles in ice, water or steam. ice is diagram … explanation … … water is diagram … explanation … … steam is diagram … explanation … … [3] (b) A few drops of water are left in a cup in a warm room. After a few hours, no water is left in the cup. State the name of the process that has occurred. … [1] (c) Water is neutral. State the pH number of pure water. pH = … [1] (d) State why chlorine is added to water to make it safe to drink. … … [1] (e) The electronic structures for oxygen and hydrogen are shown in Fig. 5.2. x O H Fig. 5.2 Complete the dot‑and‑cross diagram in Fig. 5.3 to show the arrangement of electrons in a molecule of water. Show the outer‑shell electrons only. O H H Fig. 5.3 [2] (f) Sodium chloride is a solute. Water is a solvent. Define the terms solute and solvent. solute … … solvent … … [2] [Total: 10]

10 marks

Mark scheme: 5(a) ice is C – particles are in regular arrangement water is B – particles are (mostly) touching and irregular arrangement steam is A – particles are widely spaced C B A ; one correct explanation ; three correct explanations ; 3 5(b) evaporation ; 1 5(c) 7 ; 1 5(d) kills bacteria ; 1 Question Answer Marks 5(e) 1 pair of bonding electrons ; all else correct ; 2 5(f) a solute – a substance that is dissolved in a solvent ; a solvent – a substance / liquid that dissolves a solute ; 2

This question in 0654/31 May/June 2024

5 (a) The formulae of six gases found in the air are shown. CO CO2 He H2O N2 O2 Using these formulae: (i) State the formula for a monatomic gas. … [1] (ii) State the formula for a toxic gas. … [1] (iii) State the formula for the gas that makes up 78% of clean dry air. … [1] (iv) State the formula for an element. … [1] (v) State the formulae for the two substances that are needed to cause iron to rust. … and … [2] (b) Hydrogen chloride is a gas. Complete the dot‑and‑cross diagram in Fig. 5.1 to show the electron arrangement in a molecule of hydrogen chloride. Draw outer shell electrons only. H Cl Fig. 5.1 [2] (c) Hydrogen chloride dissolves in water to make dilute hydrochloric acid. Describe the effect of dilute hydrochloric acid on blue litmus indicator. … [1] (d) State the names of the two gaseous elements used in a fuel cell to produce electricity. 1 … 2 … [2] [Total: 11]

11 marks

Mark scheme: 5(a)(i) He ; 1 5(a)(ii) CO ; 1 5(a)(iii) N2 ; 1 5(a)(iv) He or N2 or O2 ; 1 5(a)(v) O2 ; 2 H2O ; 5(b) 2 shared pair correct ; all else correct ; 5(c) turns red ; 1 5(d) hydrogen ; 2 oxygen ;

This question in 0654/33 Oct/Nov 2025