2 The table shows the masses of some of the ions in 1000 cm3 of fruit juice. name of ion formula of ion mass of ion in 1000 cm3 of fruit juice / mg ammonium NH4 + 6 calcium Ca2+ 73 chloride Cl – 238 magnesium Mg2+ 77 NO3 – 10 phosphate PO4 3– 20 potassium K+ 419 Na+ 3 sulfate SO4 2– 10 (a) Answer these questions using only the information in the table. (i) State which negative ion has the highest mass in 1000 cm3 of fruit juice. … [1] (ii) Give the formulae of the ions in sodium nitrate. … and … [1] (iii) Calculate the mass of ammonium ions in 250 cm3 of fruit juice. mass = … mg [1] (b) Describe a test for chloride ions. test … observations … [2] (c) Phosphate ions, PO4 3–, are present in most fertilisers. Phosphate ions contain phosphorus. (i) State the names of two other elements that are in most fertilisers. 1 … 2 … [2] (ii) Explain why farmers put fertilisers on fields where crops are to be grown. … … [1] (d) A student heated ammonium sulfate with sodium hydroxide in a test-tube. (i) Complete the equation for this reaction. (NH4)2SO4 + …NaOH → …NH3 + Na2SO4 + 2H2O [2] (ii) Concentrated aqueous ammonia releases fumes of ammonia gas. A long glass tube is set up as shown. long glass tube cotton wool soaked in concentrated aqueous ammonia damp red litmus paper At first, the red litmus paper does not turn blue. After a short time, the litmus paper turns blue. Explain these observations using the kinetic particle model. … … … … … [3] [Total: 13]

2(a)(i) Cl – / chloride 1 2(a)(ii) Na+ AND NO3– 1 2(a)(iii) 1.5 (mg) 1 2(b) add (aqueous acidified) silver nitrate (1) white precipitate / white solid (1) 2 2(c)(i) potassium (1) nitrogen (1) 2 2(c)(ii) to improve crop yield / to replace nitrogen (or other elements) lost from soil (by being absorbed by plants) / to replace nitrogen (or other elements) absorbed by plants 1 2(d)(i) 2 (NaOH) (1) 2 (NH3) (1) 2 2(d)(ii) 1 mark each for any 3 of: • (NH3) molecules escape from solution • diffusion • molecules in (constant) movement / molecules collide / molecules travel • (movement of) molecules is random / haphazard / in every direction • molecules spread out / molecules mix • (molecules spread) from high(er) concentration to low(er) concentration • molecules hit the litmus paper / molecules 3 (a) To earn marks, you must correctly identify the negative ion with the highest mass, provide the correct formulae for the ions in sodium nitrate, and calculate the correct mass of ammonium ions in 250 cm³ of fruit juice. (b) To earn marks, you must describe adding acidified silver nitrate solution and state that a white precipitate is observed. (c) To earn marks, you must name two other elements found in most fertilisers and explain why fertilisers are used.

3 The table shows some properties of four Group I elements. element melting point / °C boiling point / °C atomic radius / nm sodium 98 883 0.191 potassium 63 760 rubidium 39 0.250 caesium 29 671 0.272 (a) (i) Complete the table by predicting: ● the boiling point of rubidium ● the atomic radius of potassium. [2] (ii) Describe the trend in the melting point of the Group I elements down the group. … [1] (iii) Deduce the physical state of potassium at 60 °C. Explain your answer. … … … [2] (b) Caesium is a radioactive element with a proton number of 55. (i) Define proton number. … [1] (ii) State one industrial use of radioactive isotopes. … [1] (c) Sodium hydride, NaH, reacts with iron(III) oxide. (i) Balance the equation for this reaction. Fe2O3 + 3NaH → …Fe + …NaOH [2] (ii) Explain how this equation shows that iron(III) oxide is reduced. … [1] [Total: 10]

3(a)(i) boiling point of Rb: any values between 675 and 755 (°C) (inclusive of these values) (1) atomic radius of K: any values between 0.195 and 0.245 (nm) (inclusive of these values) (1) 2 3(a)(ii) decreases (1) 1 3(a)(iii) solid (1) 60 °C is below the melting point / the melting point is above 60 °C (1) 2 3(b)(i) number of protons in the nucleus of an atom / number of positive charges in the nucleus of an atom 1 3(b)(ii) any suitable, e.g. detecting leaks in pipes / measuring thickness of paper / energy production 1 3(c)(i) 2 (Fe) (1) 3 (NaOH) (1) 2 3(c)(ii) iron(III) oxide loses oxygen / it loses oxygen 1 (a) To earn marks, you must predict a boiling point for rubidium within the given range and an atomic radius for potassium within the given range, state that the melting point decreases, and correctly identify potassium as a solid at 60°C because 60°C is below its melting point. (b) To earn marks, you must define proton number as the number of protons in the nucleus and state a valid industrial use of radioactive isotopes.

3 The diagram shows a blast furnace used in the extraction of iron. mixture of iron ore, coke and limestone molten slag molten iron E B C D (a) Air is blown into the furnace. State which letter on the diagram, B, C, D or E, shows where air is blown into the furnace. … [1] (b) (i) Complete the chemical equation for the reduction of iron(III) oxide in the blast furnace. Fe2O3 + 3C → …Fe + …CO [2] (ii) Explain how this equation shows that iron(III) oxide is reduced. … [1] (c) Calcium carbonate (limestone) is added to the blast furnace. The calcium carbonate undergoes thermal decomposition. (i) Complete the word equation for this reaction. calcium carbonate → … … + … … [2] (ii) One of the products of this reaction reacts with impurities in the iron to form slag. Use the information in the diagram to suggest how you know that molten slag is less dense than molten iron. … [1] (d) (i) Use words from the list to complete these sentences about how steel is made from iron. acidic basic chlorides methane neutral nitrogen oxides oxygen sulfates A gas is blown through the molten iron. The name of this gas is … . Acidic gases are formed. These acidic gases react with … … . [3] (ii) State one use of mild steel. … [1] (iii) Metals such as chromium are added to iron to make stainless steel. The symbol for an isotope of chromium is shown. 53Cr 24 Deduce the number of electrons, neutrons and protons in one atom of this isotope of chromium. number of electrons … number of neutrons … number of protons … [3] (e) Chromium conducts electricity and is shiny. Give two other physical properties of chromium that are characteristic of all metals. 1 … 2 … [2] [Total: 16]

3(a) E 1 3(b)(i) 2 (Fe) (1) 3 (CO) (1) 2 3(b)(ii) iron oxide loses oxygen / it loses oxygen 1 3(c)(i) calcium oxide (1) carbon dioxide (1) 2 3(c)(ii) slag floats above the iron 1 3(d)(i) oxygen (1) basic (1) oxides (1) 3 3(d)(ii) car bodies / machinery 1 3(d)(iii) electrons: 24 (1) neutrons: 29 (1) protons: 24 (1) 3 3(e) 1 mark each for any two of: • conducts heat • malleable • ductile 2 (a) To earn this mark, you must correctly identify E as the letter showing where air is blown into the furnace. (b)(i) To earn the first mark, you must correctly balance the Fe as 2. To earn the second mark, you must correctly balance the CO as 3. (b)(ii) To earn this mark, you must explain that iron oxide loses oxygen or that it loses oxygen. (c)(i) To earn the first mark, you must state 'calcium oxide' as a product. To earn the second mark, you must state 'carbon dioxide' as the other product. (c)(ii) To earn this mark, you must state that slag floats above the iron. (d)(i) To earn the first mark, you must state 'oxygen'. To earn the second mark, you must state 'basic'. To earn the third mark, you must state 'oxides'. (d)(ii) To earn this mark, you must provide a correct use such as 'car bodies' or 'machinery'. (d)(iii) To earn the first mark, you must state 24 for electrons. To earn the second mark, you must state 29 for neutrons. To earn the third mark, you must state 24 for protons. (e) To earn two marks, you must provide any two correct properties from the list: conducts heat, malleable, or ductile.

3 Iron is extracted from iron ore in a blast furnace. (a) Name an ore of iron. … [1] (b) (i) Complete the chemical equation for the reduction of iron(III) oxide in the blast furnace. Fe2O3 + …CO → …Fe + 3CO2 [2] (ii) State the meaning of the term reduction. … [1] (c) Calcium carbonate (limestone) is added to the blast furnace. The calcium carbonate undergoes thermal decomposition. State the meaning of the term thermal decomposition. … … [2] (d) Iron can be made into stainless steel. (i) Give one use of stainless steel. … [1] (ii) Describe one advantage of stainless steel compared with pure iron. … … [1] (e) The symbol for an isotope of iron is shown. 57Fe 26 Deduce the number of electrons, neutrons and protons in one atom of this isotope of iron. number of electrons … number of neutrons … number of protons … [3] (f) Iron is a good conductor of heat and electricity. Give two other physical properties of iron that are characteristic of all metals. 1 … 2 … [2] (g) Iron rusts. Name the two substances needed for iron to rust. 1 … 2 … [2] [Total: 15]

3(a) hematite 1 3(b)(i) 3 (CO) (1) 2 (Fe) (1) 2 3(b)(ii) loss of oxygen (from a compound) 1 3(c) breaking down of a compound (1) by heat / by heating (1) 2 3(d)(i) cutlery / chemical plant 1 3(d)(ii) reduced corrosion / harder / stronger 1 3(e) electrons: 26 (1) neutrons: 31 (1) protons: 26 (1) 3 3(f) 1 mark each for any 2 of: • lustrous / shiny • malleable • ductile 2 3(g) oxygen (1) water (1) 2 (a) To earn the mark, you must name a correct ore of iron, such as hematite. (b) To earn marks, you must correctly balance the chemical equation for the reduction of iron(III) oxide and state that reduction means the loss of oxygen from a compound. (c) To earn marks, you must state that thermal decomposition is the breaking down of a compound by heat or heating. (d) To earn marks, you must give a correct use of stainless steel and describe one advantage it has over pure iron, such as reduced corrosion, being harder, or stronger. (e) To earn marks, you must correctly state the number of electrons, neutrons, and protons for the iron atom. (f) To earn marks, you must list any two correct physical properties of metals, such as being lustrous, malleable, or ductile. (g) To earn marks, you must identify oxygen and water as the substances needed for iron to rust.

Cambridge IGCSE Chemistry · 0620

IGCSE Chemistry (0620) Chemical reactions past paper questions

Questions on rate of reaction, reversible reactions and equilibrium, and redox.

689 free questions from 2016–2021, each with its marking scheme. Open the full topical bank to filter by subtopic, paper, and year.

Chemical reactions in IGCSE Chemistry 0620 exams, 2020–2025

Across 2020–2025, Chemical reactions accounted for 690 questions worth 3,232 marks in Cambridge IGCSE Chemistry (0620) papers.

By year
Year	Questions	Marks
2020	124	519
2021	108	500
2022	121	606
2023	113	553
2024	119	557
2025	105	497

Most-tested subtopics

6.2 Rate of reaction1492 marks
6.4 Redox1107 marks
6.3 Reversible reactions and equilibrium575 marks

Appears in

Paper 1 · 197 qs
Paper 2 · 263 qs
Paper 3 · 104 qs
Paper 4 · 78 qs
Paper 5 · 19 qs
Paper 6 · 29 qs

All most-tested Chemistry topics

2021 May/Jun · Paper 3 · Q2 · 13 marks
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2021 May/Jun · Paper 3 · Q3 · 10 marks
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2021 Oct/Nov · Paper 3 · Q3 · 16 marks
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2021 Oct/Nov · Paper 3 · Q3 · 15 marks
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2021 Feb/Mar · Paper 1 · Q9 · 1 mark
Marking scheme
Mark scheme — 2021 Paper 1 Q9
Answer: D
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