IGCSE Chemistry 0620 Paper 31, May/June 2025

an element which forms an ion with a 1+ charge

a metal that is extracted in the blast furnace

a soft metal that is more reactive than sodium

approximately 78% of clean, dry air

a gas that is identified using damp red litmus paper

a liquid at room temperature and pressure

an element used in food containers because of its resistance to corrosion

a transition element.

Table 2.1 shows the masses of the compounds formed when 1000 cm${}^3$ of sea water is evaporated. Table 2.1

Answer these questions, using the information from Table 2.1. State the chemical name of ${\text{CaCO}}_3$.

The total mass of compounds formed from 1000 cm${}^3$ of sea water is 19.0 g. Calculate the total mass of compounds formed from 1750 cm${}^3$ of sea water. mass = .............................. g

Magnesium sulfate is soluble in water. Choose one other compound that is soluble in water. Tick (✓) one box. lead(II) chloride [ ] magnesium carbonate [ ] potassium hydroxide [ ] silver chloride [ ]

Potassium chloride is found in sea water and contains chloride ions. Describe a test for chloride ions. test ............................................................................................................................................ ................................................................................................................................................... observations ............................................................................................................................. ...................................................................................................................................................

Sodium ions are in sea water. Complete Fig. 2.1 to show: • the electronic configuration of a sodium ion • the charge on the ion.

Sodium chloride forms a liquid when heated. Describe the arrangement and motion of the particles in a liquid. arrangement ............................................................................................................................. ................................................................................................................................................... motion ....................................................................................................................................... ...................................................................................................................................................

Sodium chloride is an ionic compound that dissolves in water. State two other properties of an ionic compound. 1 ................................................................................................................................................ 2 ................................................................................................................................................

Sea water contains dissolved gases. Name the gas that is essential for aquatic life.

Explain why sulfur is placed in Group VI of the Periodic Table.

Two isotopes of sulfur are shown in Fig. 3.1. ${}_{16}^{33}\text{S}$ ${}_{16}^{36}\text{S}$ Fig. 3.1 Complete Table 3.1 to show the number of protons, neutrons and electrons in one atom of these isotopes. Table 3.1

Sulfur dioxide is an air pollutant. State one source of sulfur dioxide in the air.

State one adverse effect on the environment of sulfur dioxide.

Sulfur dioxide reacts with hydrogen sulfide. Complete the symbol equation for this reaction. $${\text{SO}}_2+2{\text{H}}_2\text{S}\to \mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\text{S}+\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}{\text{H}}_2\text{O}$$

State the type of bonding between the atoms in sulfur dioxide.

A compound of sulfur has the formula ${\text{Al}}_2({\text{SO}}_4{)}_3$. Complete Table 3.2 to calculate the relative formula mass of ${\text{Al}}_2({\text{SO}}_4{)}_3$. Table 3.2

relative formula mass = ..............................

Name the process that separates petroleum into its useful components.

Fuel oil is obtained from petroleum. State one use of fuel oil.

Natural gas is a fossil fuel. Draw a circle around one compound that is the main constituent of natural gas. carbon dioxide ethane ethanol methane

Describe how long chain hydrocarbon molecules can be made into short chain molecules. Include in your answer: • the name of this process • the conditions needed for this process to take place • the products of this process.

State one reason why long chain hydrocarbon molecules are made into short chain hydrocarbon molecules.

Draw the displayed formula of a molecule of ethane.

Ethanol is manufactured by fermentation of aqueous glucose. State two conditions for fermentation. 1 ........................................................................................................................................ 2 ........................................................................................................................................

State one use of ethanol.

Fig. 4.1 shows the displayed formula of an organic molecule. Fig. 4.1 Deduce the molecular formula of this molecule.

Explain why the molecule in Fig. 4.1 is unsaturated.

A student investigates the reaction of four different metals, A, B, C and D, with dilute hydrochloric acid. All other conditions are the same in each test-tube. The results of the experiment are shown in Fig. 5.1. Put the metals, A, B, C and D, in their order of reactivity. most reactive .............................. .............................. .............................. least reactive ..............................

One way the student can increase the rate of the reaction in the experiment is to use a higher concentration of acid. State two other ways to increase the rate of this reaction. 1 ........................................................................................................................................ 2 ........................................................................................................................................

Hydrogen gas is produced in this experiment. Describe a test for hydrogen gas. test .................................................................................................................................... observations ...................................................................................................................... ...........................................................................................................................................

State the formula of the ion that is present in all acids.

Stainless steel is an alloy. State the meaning of the term alloy.

State one property of stainless steel that makes it suitable for cutlery.

Complete the word equation to show the reaction between magnesium carbonate and nitric acid. magnesium carbonate + nitric acid $\to$ ......................... + ......................... + .........................

Crystals of copper(II) chloride are prepared by adding excess copper(II) oxide powder to dilute hydrochloric acid. Describe how to prepare a sample of pure, dry copper(II) chloride crystals after the reaction is complete. In your answer, describe how to: • remove the excess copper(II) oxide from the reaction mixture • crystallise the copper(II) chloride • dry the crystals.

Fig. 6.1 shows the apparatus for the electrolysis of molten lithium iodide, using inert electrodes. Label Fig. 6.1 to show the: • anode • molten lithium iodide.

Platinum metal is used as an inert electrode in this electrolysis experiment. Name one other suitable material that can be used as an inert electrode.

Name the products formed at the positive and negative electrodes when molten lithium iodide is electrolysed. positive electrode .............................................................................................................. negative electrode .............................................................................................................

Table 6.2 shows some properties of five compounds, A, B, C, D and E. Table 6.2

State which two of the compounds, A, B, C, D and E, are simple molecules. Give two reasons for your answer. compounds ............................................................ and ........................................................... reason 1 .................................................................................................................................... reason 2 ....................................................................................................................................

Table 7.1 shows the results of four experiments. Table 7.1

State which experiment shows the greatest temperature change.

In experiment 4, zinc was added to dilute hydrochloric acid. Complete the symbol equation. $$\text{Zn}+\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\text{HCl}\to {\text{ZnCl}}_2+\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}$$

Fig. 7.1 shows the incomplete reaction pathway diagram for the reaction in Experiment 4. Complete Fig. 7.1 by labelling: • the vertical axis • the reactants • the products.

Fig. 7.2 shows the changes of state of copper. Name the changes of state labelled G and H. G ............................................................................................................................................... H ...............................................................................................................................................

River water needs to be treated to make it safe to drink. Two of the stages used in the treatment of domestic water are the addition of carbon and chlorination. Describe the reason for each of these stages. addition of carbon ..................................................................................................................... ................................................................................................................................................... chlorination ............................................................................................................................... ...................................................................................................................................................

Describe how to test whether a sample of water is pure using boiling point.

Explain why distilled water is used in practical chemistry rather than tap water.

A sample of polluted air contains carbon monoxide and methane. State one harmful effect of each of these air pollutants. carbon monoxide ...................................................................................................................... methane ....................................................................................................................................