IGCSE Chemistry 0620 Paper 43, May/June 2025

is a compound with a giant covalent structure

is an unsaturated hydrocarbon

is an amphoteric oxide

is a good conductor of electricity when solid

contains simple molecules with 9 atoms

react together to form slag in the blast furnace ................................................................... and ..................................................................

belongs to a homologous series whose general formula is ${\mathrm{C}}_n{\mathrm{H}}_{2n+2}$

is manufactured by the catalytic addition of steam to ethene

is a gas that is approximately 78% of clean, dry air.

State which of these particles are found in the nucleus of an atom.

Atoms of the same element are known as isotopes. ${}_{16}^{32}\mathrm{S}$ and ${}_{16}^{34}\mathrm{S}$ are isotopes of sulfur. Complete Table 2.1 to show the number of electrons, neutrons and protons in one atom or ion of these isotopes. Table 2.1

Table 2.2 shows the relative masses and the percentage abundances of the two isotopes in a sample of sulfur. Table 2.2

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

The relative atomic masses of all elements are compared to one atom of an isotope. Identify this isotope.

Ions are atoms or groups of atoms that have gained or lost one or more electrons. An oxygen atom has the electronic configuration of 2,6. Give the formula of one atom and one positive ion that has the same electronic configuration as ${\mathrm{O}}^{2-}$. • atom .................................................................................................................. • positive ion ........................................................................................................................

Zinc is held together by electrostatic forces of attraction between particles. Name the type of bonding in zinc.

Name the two types of particles held together by the bonding in (a)(i). 1 ........................................................................................................................................ 2 ........................................................................................................................................

Name the type of particle whose movement allows zinc to conduct electricity.

Zinc is present in alloys such as brass. State the meaning of the term alloy.

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

Zinc sulfate crystals are made by the reaction between zinc carbonate and dilute sulfuric acid, using the following steps. step 1 An excess of powdered zinc carbonate is added to dilute sulfuric acid. step 2 Excess zinc carbonate is separated from aqueous zinc sulfate by filtration. step 3 Aqueous zinc sulfate is heated until a saturated solution is formed. step 4 The saturated solution is allowed to cool and crystallise. step 5 The crystals are removed and dried. Give two observations which show that the zinc carbonate is in excess in step 1. 1 ........................................................................................................................................ 2 ........................................................................................................................................

Name the filtrate in step 2.

Name a compound, other than zinc carbonate, that can be added to dilute sulfuric acid to produce aqueous zinc sulfate in step 1.

State what is meant by the term saturated solution.

Step 1 is repeated using large pieces of zinc carbonate instead of powdered zinc carbonate. All other conditions are the same. The rate of reaction decreases. Explain why the rate of reaction decreases. Give your answer in terms of particles.

Hydrated crystals form in step 4. State what is meant by the term hydrated.

Sulfuric acid is manufactured in a four-stage process. stage 1 Sulfur dioxide is produced from ores containing sulfur. stage 2 Sulfur dioxide reacts with oxygen to form sulfur trioxide. stage 3 Sulfur trioxide reacts with concentrated sulfuric acid to form oleum, ${\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7$. stage 4 Oleum reacts with water to form concentrated sulfuric acid. Iron pyrite is an ore containing sulfur. The ore contains a compound with the formula ${\mathrm{F}\mathrm{e}\mathrm{S}}_2$. ${\mathrm{F}\mathrm{e}\mathrm{S}}_2$ reacts with oxygen in the air to produce sulfur dioxide. Balance the symbol equation for this reaction. $$4{\mathrm{F}\mathrm{e}\mathrm{S}}_2+\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}{\mathrm{O}}_2\to \mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}{\mathrm{S}\mathrm{O}}_2+\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}{\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3$$

Complete the dot-and-cross diagram in Fig. 4.1 to show the electronic configuration in an oxygen molecule, ${\mathrm{O}}_2$. Show outer-shell electrons only. Fig. 4.1

State three typical conditions for the reaction between sulfur dioxide and oxygen in stage 2. 1 ........................................................................................................................................ 2 ........................................................................................................................................ 3 ........................................................................................................................................

Write a symbol equation for the reaction that occurs in stage 2.

Write the symbol equation for the reaction in stage 3.

Sulfuric acid reacts with carbon. The equation for the reaction is shown. $$2{\mathrm{H}}_2{\mathrm{S}\mathrm{O}}_4+\mathrm{C}\to {\mathrm{C}\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}+2{\mathrm{S}\mathrm{O}}_2$$ Give the oxidation number of carbon in: • C .............................. • ${\mathrm{C}\mathrm{O}}_2$ ..............................

Dilute sulfuric acid reacts with sodium hydrogencarbonate, ${\mathrm{N}\mathrm{a}\mathrm{H}\mathrm{C}\mathrm{O}}_3$, to produce carbon dioxide gas, ${\mathrm{C}\mathrm{O}}_2$. $${\mathrm{H}}_2{\mathrm{S}\mathrm{O}}_4(\mathrm{a}\mathrm{q})+2{\mathrm{N}\mathrm{a}\mathrm{H}\mathrm{C}\mathrm{O}}_3(\mathrm{s})\to {\mathrm{N}\mathrm{a}}_2{\mathrm{S}\mathrm{O}}_4(\mathrm{a}\mathrm{q})+2{\mathrm{C}\mathrm{O}}_2(\mathrm{g})+2{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$$ $4.20\mathrm{g}$ of ${\mathrm{N}\mathrm{a}\mathrm{H}\mathrm{C}\mathrm{O}}_3$ is added to excess dilute sulfuric acid. Calculate the volume of ${\mathrm{C}\mathrm{O}}_2(\mathrm{g})$, measured at r.t.p., produced using the following steps. • Calculate the number of moles of ${\mathrm{N}\mathrm{a}\mathrm{H}\mathrm{C}\mathrm{O}}_3$ in $4.20\mathrm{g}$. The $M_r$ of ${\mathrm{N}\mathrm{a}\mathrm{H}\mathrm{C}\mathrm{O}}_3$ is 84. ..............................mol • Deduce the number of moles of ${\mathrm{C}\mathrm{O}}_2(\mathrm{g})$ that are produced. ..............................mol • Calculate the volume of ${\mathrm{C}\mathrm{O}}_2(\mathrm{g})$ produced in ${\mathrm{c}\mathrm{m}}^3$. One mole of any gas occupies $24000{\mathrm{c}\mathrm{m}}^3$ at r.t.p. .............................. ${\mathrm{c}\mathrm{m}}^3$

State two characteristics of an equilibrium. 1 ................................................................................................................................................ 2 ................................................................................................................................................

Both a high yield of ethanoic acid and a high rate of reaction are needed. The reaction is carried out at $300{}^{\circ }\mathrm{C}$. The forward reaction is exothermic. State the disadvantage of using a temperature: • below $300{}^{\circ }\mathrm{C}$ ........................................................................................................................................... • above $300{}^{\circ }\mathrm{C}$. ...........................................................................................................................................

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

Suggest which element from the list is a suitable catalyst for the reaction. Give a reason for your answer. aluminium carbon cobalt magnesium sodium catalyst .............................................................................................................................. reason ...............................................................................................................................

Ethanoic acid is a member of the carboxylic acid homologous series. Name the carboxylic acid that contains only one carbon atom.

State the molecular formula of a carboxylic acid that contains four carbon atoms.

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

Propyl butanoate is an ester. Name the carboxylic acid and alcohol that react to produce propyl butanoate. carboxylic acid ................................................................................................................... alcohol ...............................................................................................................................

An organic compound has the following composition by mass: $\mathrm{C},58.82\mathrm{\%};\mathrm{H},9.80\mathrm{\%};\mathrm{O},31.38\mathrm{\%}$. Calculate the empirical formula of the compound. empirical formula = ..............................

State the name given to Group I elements.

State which Group I element is least reactive.

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

Write a symbol equation for this reaction.

Group I elements have lower melting points and lower boiling points than transition elements. Describe two other physical properties of Group I elements that are different from transition elements. 1 ................................................................................................................................................ 2 ................................................................................................................................................

The Group VII elements are known as the halogens. Give the physical state and colour of chlorine at room temperature and pressure. state .................................................................................................................................. colour ................................................................................................................................

When chlorine is passed through aqueous potassium bromide, a displacement reaction occurs. The equation for the reaction is shown. $${\mathrm{C}\mathrm{l}}_2+2\mathrm{K}\mathrm{B}\mathrm{r}\to 2\mathrm{K}\mathrm{C}\mathrm{l}+{\mathrm{B}\mathrm{r}}_2$$ Write an ionic equation for the reaction.

Iodine and chlorine react at high temperatures to form iodine monochloride, $\mathrm{I}\mathrm{C}\mathrm{l}$. The equation for the reaction is shown. $${\mathrm{I}}_2(\mathrm{g})+{\mathrm{C}\mathrm{l}}_2(\mathrm{g})\to 2\mathrm{I}\mathrm{C}\mathrm{l}(\mathrm{g})$$ The structures of the molecules involved in the reaction are $\mathrm{I}-\mathrm{I}$, $\mathrm{C}\mathrm{l}-\mathrm{C}\mathrm{l}$ and $\mathrm{I}-\mathrm{C}\mathrm{l}$. 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 ${\mathrm{C}\mathrm{l}}_2(\mathrm{g})$. ..............................kJ • Calculate the total amount of energy released when the bonds in $2\mathrm{m}\mathrm{o}\mathrm{l}$ of $\mathrm{I}\mathrm{C}\mathrm{l}(\mathrm{g})$ are formed. .............................. kJ • Calculate the enthalpy change, $\mathrm{\Delta }H$, for the reaction. Your answer should include a sign. .............................. kJ/mol