IGCSE Chemistry 0620 Paper 41, May/June 2025

is a basic oxide

contains carbon atoms only

is manufactured by fermentation

is produced by the decomposition of vegetation

contains aluminium oxide

causes acid rain

is a simple molecule with 11 atoms

is produced when limestone thermally decomposes in the blast furnace

is a gas that is approximately 21% of clean, dry air

is a monomer in addition polymerisation.

Complete Table 2.1. Table 2.1

Atoms of the same element are known as isotopes. ${}_{19}^{39}\mathrm{K}$ and ${}_{19}^{41}\mathrm{K}$ are isotopes of potassium. Complete Table 2.2 to show the number of electrons, neutrons and protons in one atom or ion of these isotopes. Table 2.2

Table 2.3 shows the relative masses and the percentage abundances of the two isotopes in a sample of potassium. Table 2.3

Calculate the relative atomic mass of this sample of potassium to one decimal place. relative atomic mass = ..............................

An isotope of aluminium has a nucleon number of 27. Aluminium has a relative atomic mass of 27. State what conclusion can be made from this information.

A calcium atom has the electronic configuration of 2,8,8,2. Give the formula of one atom and one negative ion that has the same electronic configuration as ${\mathrm{C}\mathrm{a}}^{2+}$. • atom .................................................................................................................. • negative ion .......................................................................................................

Describe the bonding in a metallic element such as copper.

Explain how solid copper conducts electricity.

Copper is in alloys such as brass. State one reason why alloys are more useful than pure metals.

Name the substance that is present in brass, other than copper.

Copper(II) sulfate crystals are made by the reaction between copper(II) carbonate and dilute sulfuric acid, using the following steps. The sulfuric acid has a concentration of $0.100\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}\mathrm{d}{\mathrm{m}}^3$. step 1 Powdered copper(II) carbonate is added to dilute sulfuric acid. The mixture is stirred. A reaction occurs. step 2 More copper(II) carbonate is added, with stirring, until the reaction stops. step 3 Unreacted copper(II) carbonate is separated from aqueous copper(II) sulfate by filtration. step 4 Aqueous copper(II) sulfate is heated until some of the water evaporates. step 5 The remaining solution is allowed to cool and crystallise. step 6 The crystals are removed and dried. Give two observations in step 1. 1 ........................................................................................................................................ 2 ........................................................................................................................................

State why the reaction stops in step 2.

Name the residue in step 3.

Name a substance, other than copper(II) carbonate, that can be added to dilute sulfuric acid to produce aqueous copper(II) sulfate.

The solution at the end of step 4 contains the maximum amount of copper(II) sulfate that will dissolve at that temperature. State the term used to describe this type of solution.

Step 1 is repeated using sulfuric acid of concentration $0.200\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}\mathrm{d}{\mathrm{m}}^3$ instead of $0.100\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}\mathrm{d}{\mathrm{m}}^3$. All other conditions are the same. The rate of reaction increases. Explain why the rate of reaction increases. Give your answer in terms of particles.

Copper(II) sulfate crystals have the formula $\mathrm{C}\mathrm{u}\mathrm{S}{\mathrm{O}}_4\cdot 5{\mathrm{H}}_2\mathrm{O}$. State the term used to describe a substance that is chemically combined with water.

Complete the dot-and-cross diagram in Fig. 4.1 to show the electronic configuration in a nitrogen molecule. Show outer-shell electrons only. Fig. 4.1

Ammonia, $\mathrm{N}{\mathrm{H}}_3$, is manufactured by reacting nitrogen with hydrogen, ${\mathrm{H}}_2$, in the Haber process. State three typical conditions for the reaction between nitrogen and hydrogen in the Haber process. 1 ........................................................................................................................................ 2 ........................................................................................................................................ 3 ........................................................................................................................................

Write the symbol equation for the chemical reaction in the Haber process.

Ammonia is converted into nitric acid in a two-step process. In step 1, ammonia and oxygen are passed over a catalyst. Balance the symbol equation for this reaction. $4\mathrm{N}{\mathrm{H}}_3+\dots \dots {\mathrm{O}}_2\rightleftharpoons \dots \dots \mathrm{N}\mathrm{O}+\dots \dots {\mathrm{H}}_2\mathrm{O}$

Give the oxidation number of nitrogen in: • $\mathrm{N}{\mathrm{H}}_3$ .............................. • $\mathrm{N}\mathrm{O}$. ..............................

Define oxidation in terms of oxidation number.

In step 2, oxygen and water react with NO to produce nitric acid as the only product. Write a symbol equation for this chemical reaction.

Ammonia is converted into ammonium sulfate, $(\mathrm{N}{\mathrm{H}}_4{)}_2\mathrm{S}{\mathrm{O}}_4$. $$2\mathrm{N}{\mathrm{H}}_3(\mathrm{g})+{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4(\mathrm{a}\mathrm{q})\to (\mathrm{N}{\mathrm{H}}_4{)}_2\mathrm{S}{\mathrm{O}}_4(\mathrm{s})$$ $360\mathrm{d}{\mathrm{m}}^3$ of ammonia gas, measured at r.t.p., reacts with excess sulfuric acid. Calculate the mass of ammonium sulfate produced, using the following steps. • Calculate the number of moles of $\mathrm{N}{\mathrm{H}}_3(\mathrm{g})$ in $360\mathrm{d}{\mathrm{m}}^3$. One mole of any gas occupies $24\mathrm{d}{\mathrm{m}}^3$ at r.t.p. .............................. mol • Calculate the number of moles of $(\mathrm{N}{\mathrm{H}}_4{)}_2\mathrm{S}{\mathrm{O}}_4$ produced. .............................. mol • Calculate the mass of $(\mathrm{N}{\mathrm{H}}_4{)}_2\mathrm{S}{\mathrm{O}}_4$ produced. The $M_r$ of $(\mathrm{N}{\mathrm{H}}_4{)}_2\mathrm{S}{\mathrm{O}}_4$ is 132. .............................. g

State what happens to the concentration of $\mathrm{C}{\mathrm{H}}_3\mathrm{O}\mathrm{H}$ when the reaction is at equilibrium. Explain your answer in terms of rate of forward and reverse reactions.

The reaction is carried out at a pressure of 75 atmospheres and a temperature of $250{}^{\circ }\mathrm{C}$. State two disadvantages of using a pressure below 75 atmospheres. 1 ........................................................................................................................................ 2 ........................................................................................................................................

Complete Table 5.1 using only the words increases, decreases or no change. Table 5.1

If a temperature of more than $250{}^{\circ }\mathrm{C}$ is used, the yield of methanol decreases. State what can be deduced about the forward reaction.

Suggest which of the elements from the list is a suitable catalyst for the reaction. Give a reason for your answer. barium carbon copper potassium sulfur catalyst .............................................................................................................................. reason ...............................................................................................................................

Methanol is a member of the homologous series of alcohols. State two characteristics of all members of a homologous series. 1 ........................................................................................................................................ 2 ........................................................................................................................................

State the molecular formula of an alcohol that contains five carbon atoms.

Carboxylic acids react with alcohols to form esters. Draw the displayed formula of an ester which contains three carbon atoms.

Butyl ethanoate is an ester. Name the alcohol and the carboxylic acid that react to produce butyl ethanoate. alcohol ............................................................................................................................... carboxylic acid ...................................................................................................................

An organic compound has the following composition by mass: C, 64.87%; H, 13.51%; O, 21.62%. Calculate the empirical formula of the compound. empirical formula = ..............................

State the name given to Group VII elements.

State which Group VII element is most reactive.

Give the physical state and colour of iodine at room temperature and pressure. state .......................................................................................................................................... colour ........................................................................................................................................

When bromine is added to aqueous potassium iodide a displacement reaction occurs. The equation for the reaction is shown. $$\mathrm{B}{\mathrm{r}}_2+2\mathrm{K}\mathrm{I}\to 2\mathrm{K}\mathrm{B}\mathrm{r}+{\mathrm{I}}_2$$ Write an ionic equation for the reaction.

Iodine and bromine react at high temperatures to form iodine monobromide, IBr. The equation is shown. $${\mathrm{I}}_2(\mathrm{g})+\mathrm{B}{\mathrm{r}}_2(\mathrm{g})\to 2\mathrm{I}\mathrm{B}\mathrm{r}(\mathrm{g})$$ The structures of the molecules involved in the reaction are I–I, Br–Br and I–Br. Table 6.1

Calculate the enthalpy change, $\mathrm{\Delta }H$, for the reaction using the bond energies in Table 6.1. Use the following steps. • Calculate the total amount of energy required to break the bonds in $1\mathrm{m}\mathrm{o}\mathrm{l}$ of ${\mathrm{I}}_2(\mathrm{g})$ and $1\mathrm{m}\mathrm{o}\mathrm{l}$ of $\mathrm{B}{\mathrm{r}}_2(\mathrm{g})$. .............................. kJ • Calculate the total amount of energy released when the bonds in $2\mathrm{m}\mathrm{o}\mathrm{l}$ of $\mathrm{I}\mathrm{B}\mathrm{r}(\mathrm{g})$ are formed. .............................. kJ • Calculate the enthalpy change, $\mathrm{\Delta }H$, for the reaction. Your answer should include a sign. .............................. kJ/mol

Sodium is in Group I of the Periodic Table. When sodium is added to water a chemical reaction occurs. Give two observations when sodium is added to water. 1 ........................................................................................................................................ 2 ........................................................................................................................................

Thymolphthalein is added to the solution when the reaction has finished. State the final colour of the thymolphthalein in the solution.