IGCSE Chemistry 0620 Paper 43, May/June 2026

a reaction that occurs in the blast furnace

a reaction catalysed by nickel

an addition reaction

photosynthesis

a reaction that occurs in the Haber process

a substitution reaction

incomplete combustion

Identify an element that: is approximately 21% of clean, dry air

Identify an element that: is in Group 1 and Period 4 of the Periodic Table

Identify an element that: contains atoms with exactly 24 protons

Identify an element that: removes tastes and odours from the domestic water supply

Identify an element that: exists as diamond

Identify an element that: forms an insoluble chloride salt.

Boron has two isotopes. State the meaning of the term isotopes.

The isotopes of boron have mass numbers of 10 and 11. The relative atomic mass of boron is 10.8. Calculate the percentage abundance of the isotope of boron with a mass number of 10. percentage abundance = .........................................................

Sodium oxide is an ionic compound. Complete the dot-and-cross diagrams in Figure 3.1 to show the bonding in sodium oxide. The inner shells of electrons are shown. Show the charge on each ion.

Sodium oxide is held together by ionic bonds. State the meaning of the term ionic bond.

The ions in sodium oxide are present in a giant ionic lattice. State the meaning of the term giant ionic lattice.

Oxygen, ${\mathrm{O}}_2$, consists of simple molecules. Complete the dot–and-cross diagram in Figure 3.2 of a molecule of oxygen. Show outer shell electrons only.

Oxygen has a low melting point. State the general term for the weak forces of attraction that cause oxygen to have a low melting point.

State the meaning of the term aqueous.

Complete the symbol equation for the decomposition of aqueous hydrogen peroxide. .....${\mathrm{H}}_2{\mathrm{O}}_2(\mathrm{a}\mathrm{q})\to$ .....${\mathrm{H}}_2\mathrm{O}(\mathrm{l})+{\mathrm{O}}_2(\mathrm{g})$

State why there is a decrease in mass of the conical flask and its contents during the experiment.

The rate of reaction is highest at the start of the reaction. The rate of reaction decreases as time increases. The rate of reaction eventually becomes zero because the reaction stops. Explain why the rate of reaction decreases as time increases.

The experiment is repeated at a higher temperature. All other conditions remain the same. Explain why the rate of reaction is greater at the higher temperature.

Oxygen is also produced by thermal decomposition of potassium manganate(VII), $\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4$. State the meaning of (VII) in potassium manganate(VII).

The equation for the reaction is shown. $$2\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4\to {\mathrm{K}}_2\mathrm{M}\mathrm{n}{\mathrm{O}}_4+\mathrm{M}\mathrm{n}{\mathrm{O}}_2+{\mathrm{O}}_2$$ Calculate the mass of $\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4$ used to produce $0.64\mathrm{g}$ of ${\mathrm{O}}_2$. [$M_r$: $\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4$, 158; ${\mathrm{O}}_2$, 32] Use the following steps. • Calculate the number of moles of ${\mathrm{O}}_2$ produced. ......................................................... mol • Calculate the number of moles of $\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4$ used. ......................................................... mol • Calculate the mass of $\mathrm{K}\mathrm{M}\mathrm{n}{\mathrm{O}}_4$ used. ............................................................. g

Concentrated aqueous lithium bromide undergoes electrolysis when electricity is passed through it. The products are: • bromine gas at the anode • hydrogen gas at the cathode. Give the term used to describe any liquid that undergoes electrolysis when electricity is passed through it.

State two properties of a substance that make it suitable to use as an electrode. 1 ........................................................................................................................................ 2 ........................................................................................................................................

Write an ionic half-equation for the formation of bromine at the anode.

Explain why hydrogen gas is produced at the cathode.

Name the type of particle responsible for the transfer of charge in any liquid that undergoes electrolysis.

Name the products formed when electricity is passed through molten lithium bromide. at the anode ...................................................................................................................... at the cathode ...................................................................................................................

Bauxite is an ore containing aluminium. Name the compound of aluminium that is present in bauxite.

Aluminium is extracted by electrolysis using cryolite. State two reasons why cryolite is used in this electrolysis. 1 ................................................................................................................................................ 2 ................................................................................................................................................

Aluminium oxide, $\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$, is an amphoteric oxide. State the meaning of the term amphoteric.

Aluminium oxide is used to make calcium aluminate. Calcium aluminate contains calcium ions, $\mathrm{C}{\mathrm{a}}^{2+}$, and aluminate ions, $\mathrm{A}\mathrm{l}{\mathrm{O}}_2^{-}$. Write the formula of calcium aluminate.

When aluminium oxide reacts with dilute hydrochloric acid, aqueous aluminium chloride and one other product are formed. Write the symbol equation for the reaction between aluminium oxide and dilute hydrochloric acid.

When aqueous silver nitrate is added to aqueous aluminium chloride, a precipitate of silver chloride, $\mathrm{A}\mathrm{g}\mathrm{C}\mathrm{l}$, is produced. Write an ionic equation for this precipitation reaction. Include state symbols.

Ammonium dichromate, $(\mathrm{N}{\mathrm{H}}_4{)}_2\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_7$, decomposes when it is heated. The products are chromium(III) oxide, $\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_3$, nitrogen and water. Ammonium dichromate is an orange solid. Identify the element which causes ammonium dichromate to be coloured.

Write the symbol equation for the reaction that occurs when ammonium dichromate is heated.

A mixture of sulfur dioxide, $\mathrm{S}{\mathrm{O}}_2$, oxygen, ${\mathrm{O}}_2$, and sulfur trioxide, $\mathrm{S}{\mathrm{O}}_3$, is allowed to reach equilibrium in a closed system in the presence of a catalyst. $$2\mathrm{S}{\mathrm{O}}_2(\mathrm{g})+{\mathrm{O}}_2(\mathrm{g})\rightleftharpoons 2\mathrm{S}{\mathrm{O}}_3(\mathrm{g})$$ The forward reaction is exothermic. State what is meant by the term closed system.

Complete Table 6.1 using the words increases, decreases or no change. Table 6.1

Name the industrial process in which sulfur dioxide is converted into sulfur trioxide.

The equation for the reaction between butane and chlorine is shown. $${\mathrm{C}}_4{\mathrm{H}}_{10}+\mathrm{C}{\mathrm{l}}_2\to {\mathrm{C}}_4{\mathrm{H}}_9\mathrm{C}\mathrm{l}+\mathrm{H}\mathrm{C}\mathrm{l}$$ Give the general formula of the homologous series which has butane as a member.

State the condition required for the reaction between butane and chlorine to occur at room temperature.

State the term given to organic compounds with the same molecular formula but different structural formulas.

Butane reacts with chlorine to make two organic compounds with the molecular formula ${\mathrm{C}}_4{\mathrm{H}}_9\mathrm{C}\mathrm{l}$. Draw the displayed formula for each of these organic compounds.

The structure of compound A is shown in Figure 7.1. Deduce the empirical formula of compound A.

State what is observed when compound A is added to the following substances. aqueous bromine .............................................................................................................. aqueous sodium carbonate ...............................................................................................

Compound A can undergo addition polymerisation to form polymer B. Draw the section of polymer B that contains two repeat units.

Polyesters are condensation polymers. Condensation polymers are made from two monomers. Name the two types of monomers used to produce polyesters. 1 ........................................................................................................................................ 2 ........................................................................................................................................

Organic compound D has the following composition by mass. C, 88.9%; H, 11.1% Calculate the empirical formula of compound D. empirical formula = .........................................................