IGCSE Chemistry 0620 Paper 42, Oct/Nov 2025

Complete Table 1.1 to describe the structures of solids, liquids and gases in terms of particle separation, particle arrangement and particle motion. Table 1.1

Substances can physically change. Name each physical change: • solid to liquid ...................................................................................................................... • gas to liquid ........................................................................................................................ • solid to aqueous. ................................................................................................................

Gases diffuse. Describe, in terms of particles, why gases diffuse.

State what determines the relative rate of diffusion of gases at constant temperature.

Gaseous oxides of nitrogen are atmospheric pollutants. One adverse effect of oxides of nitrogen is the formation of acid rain. State two other adverse effects of oxides of nitrogen. 1................................................................................................................................................. 2.................................................................................................................................................

In a catalytic converter, oxides of nitrogen are removed by reaction with the toxic gaseous product of the incomplete combustion of hydrocarbon fuels. Two non-toxic gases are formed in this reaction. Name the toxic gaseous product of the incomplete combustion of hydrocarbon fuels.

Name the two non-toxic gases formed in the catalytic converter. 1 ......................................................................................................................................... 2 .........................................................................................................................................

The iron compound in the main iron ore used in the blast furnace is iron(III) oxide. State the name of the main iron ore used in the blast furnace.

State how the main source of heat is provided in the blast furnace.

Name the gaseous reducing agent in the blast furnace.

Write a symbol equation for the reduction of iron(III) oxide by the gaseous reducing agent in (a)(iii).

The main impurity in iron ore is silicon(IV) oxide. Write two symbol equations to show the role of limestone in removing silicon(IV) oxide from iron ore. 1 ......................................................................................................................................... 2 .........................................................................................................................................

Table 2.1 shows four different isotopes of iron, A, B, C and D. Table 2.1 Explain why A, B, C and D are isotopes of iron.

Iron can form two different ions, ${\text{Fe}}^{2+}$ and ${\text{Fe}}^{3+}$. Complete Table 2.2 to show the number of protons, neutrons and electrons in the two iron ions shown. Table 2.2

Describe a test for aqueous ${\text{Fe}}^{2+}$ ions. test ..................................................................................................................................... observations....................................................................................................................... ...........................................................................................................................................

An oxidising agent converts ${\text{Fe}}^{2+}$ ions to ${\text{Fe}}^{3+}$ ions. Define the term oxidising agent.

Explain why the conversion of ${\text{Fe}}^{2+}$ ions to ${\text{Fe}}^{3+}$ ions is described as oxidation.

The oxidising agent for the conversion of ${\text{Fe}}^{2+}$ ions to ${\text{Fe}}^{3+}$ ions is aqueous potassium manganate(VII). State one condition needed for the oxidation to take place.

Iodide ions, ${\text{I}}^{-}$, reduce ${\text{Fe}}^{3+}$ ions to ${\text{Fe}}^{2+}$ ions in aqueous solution. Suggest the identity of the other product formed in this reaction.

Complete the symbol equation for the reaction. Include state symbols. ${\text{BaCl}}_2(\text{aq})+{\text{Na}}_2{\text{SO}}_4(\text{aq})\to {\text{BaSO}}_4(\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.})+\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}(\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.})$

Calculate the mass of solid ${\text{BaCl}}_2$ dissolved in step 1. mass = .............................. g

The concentration of ${\text{Na}}_2{\text{SO}}_4(\text{aq})$ in step 2 is $1.25{\text{mol/dm}}^3$. Calculate the volume, in ${\text{cm}}^3$, of $1.25{\text{mol/dm}}^3{\text{Na}}_2{\text{SO}}_4(\text{aq})$ added in step 2 which contains 0.100 moles of ${\text{Na}}_2{\text{SO}}_4$. volume = .............................. ${\text{cm}}^3$

State the colour of the solid formed in step 2.

The mixture is filtered in step 3. State the general term given to a solid left in the filter paper after filtration.

The actual mass of dry ${\text{BaSO}}_4$ collected in step 4 is greater than the expected mass. This is because the student should do an additional step between step 3 and step 4. Suggest what the student should do in this additional step, and explain why the actual mass collected is greater than the expected mass.

State the name of this method of salt preparation.

State the name of a different: • barium salt that can be used in place of ${\text{BaCl}}_2$ .................................................................. • sulfate salt that can be used in place of ${\text{Na}}_2{\text{SO}}_4$ ................................................................ • barium salt that can be made by this method. ....................................................................

One mole of each acid is added separately to $1000{\text{cm}}^3$ of distilled water to form a dilute solution. All three acids dissociate in distilled water. State the formula of the common cation produced when each of the three acids dissociates in water.

Explain, in terms of dissociation, why: • nitric acid is described as a strong acid ........................................................................................................................................... • ethanoic acid is described as a weak acid. ...........................................................................................................................................

State which of the three dilute acids will have the highest pH value.

State the colour of thymolphthalein in all three dilute acids.

Give the formula of the anion formed when: • sulfuric acid dissociates in water ........................................................................................................................................... • ethanoic acid dissociates in water. ...........................................................................................................................................

Name the two gaseous products formed during the electrolysis of dilute sulfuric acid using inert electrodes. ............................................................... and ...............................................................

Name the salt formed when calcium reacts with ethanoic acid.

Aluminium nitrate, $\text{Al}({\text{NO}}_3{)}_3$, is made when dilute nitric acid reacts with aluminium hydroxide, $\text{Al}(\text{OH}{)}_3$. $\text{Al}(\text{OH}{)}_3$ acts as a base in this reaction. Define the term base.

$\text{Al}(\text{OH}{)}_3$ is not an alkali. State what this tells you about the solubility of $\text{Al}(\text{OH}{)}_3$.

Name one other compound which forms aluminium nitrate when added to dilute nitric acid.

The oxidation number of the O atoms in $\text{Al}({\text{NO}}_3{)}_3$ is $-2$. The formula of the aluminium ion in $\text{Al}({\text{NO}}_3{)}_3$ is ${\text{Al}}^{3+}$. Determine the oxidation number of the N atoms in $\text{Al}({\text{NO}}_3{)}_3$. Show your working. oxidation number of N = ..............................

Describe two other general characteristics of the homologous series of alkanes. 1................................................................................................................................................. 2.................................................................................................................................................

State the trend in the boiling points of the alkanes as the carbon chain length increases.

Name one other physical property of alkanes that shows a trend, other than melting points and boiling points. Describe this trend as the carbon chain length of alkanes increases. name .................................................................................................................................. description..........................................................................................................................

State why alkanes are described as saturated.

Propane has the structural formula ${\text{CH}}_3{\text{CH}}_2{\text{CH}}_3$. When propane undergoes a monosubstitution reaction with chlorine at room temperature, two organic products can be formed. State one condition needed for this substitution reaction to take place.

Give the structural formula and state the name of each organic product formed. • structural formula of product 1 name of product 1....................................................................................................... • structural formula of product 2 name of product 2.......................................................................................................

The two products formed are structural isomers of each other. Define the term structural isomers.

On Fig. 6.1, draw a circle around all the atoms which make up the ester linkage.

Name compound E.

Deduce the empirical formula of compound E.

Compound E is produced when two different compounds react together in the presence of a catalyst. Name the two compounds that react together to produce compound E. 1 ......................................................................................................................................... 2 .........................................................................................................................................

Suggest a suitable catalyst for this reaction.

Determine the number of unbranched esters which have the molecular formula ${\text{C}}_5{\text{H}}_{10}{\text{O}}_2$.

All unbranched esters with the molecular formula ${\text{C}}_5{\text{H}}_{10}{\text{O}}_2$ combust completely to form carbon dioxide and water only. Write the symbol equation for the complete combustion of ${\text{C}}_5{\text{H}}_{10}{\text{O}}_2$.