IGCSE Chemistry 0620 Paper 31, Oct/Nov 2025

forms an ion which produces a red colour in a flame test

is present in diamond

forms an ion with a charge of 2–

is extracted from bauxite

is used in electrical wiring because of its good electrical conductivity and ductility.

Complete Table 2.1 to show the number of protons and neutrons in one atom of ${}_{18}^{40}\text{Ar}$. Table 2.1

Argon is an unreactive monatomic element. Explain what is meant by the term monatomic.

Explain why argon is unreactive. Give your answer in terms of electronic configuration.

At room temperature and pressure, argon is a gas. A sample of argon is placed in a sealed syringe with a freely moving plunger. Complete Table 2.2 to show the effect, if any, on the volume of argon when: • the temperature of the argon is increased • the pressure of the argon is increased. Use the words increases, decreases or no change in your answer. Table 2.2

Table 3.1 shows the masses of ions, in mg, present in a $1000{\text{ cm}}^3$ sample of river water. Table 3.1 Answer these questions using the information from Table 3.1. Name the positive ion that has the highest concentration.

State the formula of the sulfate ion.

Describe a test to identify the presence of iodide ions, ${\text{I}}^{-}$, in a sample of water. test .................................................................................................................................... ........................................................................................................................................... observations ......................................................................................................................

Calculate the mass of nitrate ions, ${\text{NO}}_3^{-}$, in $200{\text{ cm}}^3$ of river water.

Give the formulae of two ions from Table 3.1 which can be combined with potassium ions to make an NPK fertiliser.

Name two ions from Table 3.1 which lead to deoxygenation of water and damage to aquatic life.

The diagram in Fig. 3.1 shows the apparatus used to separate pure water from the sample of river water. Fig. 3.1 Name the separation method shown in Fig. 3.1.

Molecules of compound C are produced by some plants. Fig. 4.1 shows the displayed formula of a molecule of compound C. Fig. 4.1 Deduce the molecular formula of compound C to show the number of atoms of carbon, hydrogen and oxygen.

On Fig. 4.1, draw a circle around the part of the molecule which shows that the molecule is unsaturated.

A different molecule found in plants has the molecular formula ${\text{C}}_{11}{\text{H}}_{14}{\text{O}}_3$. Complete Table 4.1 to calculate the relative molecular mass of ${\text{C}}_{11}{\text{H}}_{14}{\text{O}}_3$. Table 4.1

Petroleum is a mixture of hydrocarbons which can be separated into groups of compounds called fractions. Explain what is meant by the term hydrocarbon.

Fig. 4.2 shows the names of some of the fractions obtained from petroleum using a fractionating column. Fig. 4.2 Using only the fractions shown in Fig. 4.2, name the fraction which contains compounds that: have the lowest boiling point

have the highest viscosity

are used for jet fuel.

Table 4.2 shows some properties of compounds found in the naphtha fraction. Table 4.2 A molecule of heptane contains seven carbon atoms. Deduce the molecular formula of heptane.

Use the information in Table 4.2 to predict the melting point of octane, ${\text{C}}_8{\text{H}}_{18}$.

When heated strongly in the presence of a catalyst, decane reacts to form smaller molecules. Name this type of endothermic reaction.

Ethene is one of the molecules formed when decane is heated strongly in the presence of a catalyst. Draw the displayed formula of ethene. Show all the atoms and all the bonds.

Ethene is polymerised to form the plastic poly(ethene). Name this type of polymerisation.

Describe two environmental challenges caused by the disposal of plastics such as poly(ethene). 1 ........................................................................................................................................ ........................................................................................................................................... 2 ........................................................................................................................................ ...........................................................................................................................................

Chlorine is in Group VII of the Periodic Table. Give the colour and state of chlorine at room temperature and pressure. colour ........................................................................................................................................ state ..........................................................................................................................................

State the use of chlorine in the treatment of the domestic water supply.

Iodine is in Group VII of the Periodic Table. Table 5.1 shows the melting point and the boiling point of iodine. Table 5.1 Use the information in Table 5.1 to deduce the physical state of iodine at 195°C. Give a reason for your answer. physical state ............................................................................................................................ reason ....................................................................................................................................... ...................................................................................................................................................

Potassium is an element in Group I of the Periodic Table. Elements in Group I have a low density and relatively low melting and boiling points. State one other physical property of potassium.

When a sample of potassium is added to a large container of cold water, a chemical reaction occurs. Describe what is observed when potassium is added to water.

The word equation for the reaction of potassium with water is shown. potassium + water $\to$ potassium hydroxide + hydrogen Describe a test for hydrogen. test .................................................................................................................................... observations ......................................................................................................................

Potassium reacts with oxygen to form potassium oxide, ${\text{K}}_2\text{O}$. Complete the symbol equation for this reaction. ...... K + .................... $\to 2{\text{K}}_2\text{O}$

Solid potassium oxide, ${\text{K}}_2\text{O}$, dissolves in water to form an alkali. Choose the pH value of the solution formed when solid potassium oxide is dissolved in water. Draw a circle around your chosen answer. pH 1 pH 5 pH 7 pH 12

Potassium reacts with chlorine to form the ionic compound potassium chloride. Complete the dot-and-cross diagram in Fig. 5.1 for potassium chloride to show: • the electronic configuration for each ion • the charge on each ion. Fig. 5.1

Iron is extracted from its ore using carbon (coke) and calcium carbonate in a blast furnace. Give two reasons why carbon is used in a blast furnace. 1 ........................................................................................................................................ 2 ........................................................................................................................................

Slag is a waste product of this extraction. Describe how slag is produced.

Iron ore contains iron(III) oxide. The equation for the extraction of iron from iron(III) oxide is shown. ${\text{Fe}}_2{\text{O}}_3+3\text{CO}\to 2\text{Fe}+3{\text{CO}}_2$ Explain how this equation shows that carbon monoxide is oxidised.

Pure iron is less useful than its alloys such as stainless steel. Name two metals most commonly used in stainless steel, other than iron. 1 ........................................................................................................................................ 2 ........................................................................................................................................

State one use of stainless steel.

Table 6.1 shows the observations when four different metals are added separately to dilute ethanoic acid. Table 6.1 Put the four metals in order of their reactivity. Put the least reactive metal first.

Complete the word equation for the reaction of calcium with ethanoic acid. calcium + ethanoic acid $\to$ .................... + ....................

State what is meant by the term electrolysis.

Label the cathode in Fig. 7.1.

Name one product formed at the anode.

The inert electrodes used are made of graphite. Explain what is meant by the term inert.

State one other use for graphite.

Excess solid copper(II) carbonate is added to dilute sulfuric acid. Aqueous copper(II) sulfate, water and carbon dioxide gas are produced. State with a reason if this is a chemical or a physical change.

Name a method to remove the excess copper(II) carbonate from the mixture.

Name one other substance which can be added to dilute sulfuric acid to form aqueous copper(II) sulfate.

Copper(II) sulfate, ${\text{CuSO}}_4$, exists in different forms. Draw one line from each form of copper(II) sulfate to its description. form of copper(II) sulfate description aqueous CuSO4 solid CuSO4 chemically combined with water hydrated CuSO4 CuSO4 dissolved in water anhydrous CuSO4 solid CuSO4 containing no water

Use Fig. 8.1 to deduce the time taken for the reaction to finish.

The reaction is repeated using larger pieces of magnesium of the same total mass. All other conditions stay the same. State the effect, if any, on: the time taken for the reaction to finish

the total volume of ${\text{H}}_2$ produced when the reaction is complete.

Fig. 8.2 shows the reaction pathway diagram for the reaction of magnesium with dilute hydrochloric acid. Fig. 8.2 Deduce the type of energy change shown in the diagram in Fig. 8.2. Explain your answer.