IGCSE Chemistry 0620 Paper 33, May/June 2025

an element which forms an ion with a 3– charge

a transition element

a gas that is identified using limewater

approximately 78% of clean, dry air

used in electrical wiring

the least reactive metal in the list

a diatomic molecule which is a solid at room temperature and pressure

a compound that reacts with impurities in the blast furnace to form slag

an element with a relative atomic mass of 12.

Table 2.1 shows the masses of the compounds present when a $2000{\mathrm{c}\mathrm{m}}^3$ sample of sea water is evaporated. Table 2.1 Answer these questions using the information from Table 2.1. State the chemical name of ${\mathrm{M}\mathrm{g}\mathrm{S}\mathrm{O}}_4$.

The total mass of compounds formed from $2000{\mathrm{c}\mathrm{m}}^3$ of sea water is $38.0\mathrm{g}$. Calculate the total mass of compounds present in $800{\mathrm{c}\mathrm{m}}^3$ of sea water. mass = .............................. g

Potassium chloride is soluble in water. Choose one other compound that is soluble in water. Tick (✓) one box. lead(II) sulfate magnesium carbonate silver chloride sodium hydroxide

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

Potassium chloride contains potassium ions. Complete Fig. 2.1 to show: • the electronic configuration of a potassium ion • the charge on the ion.

Sodium chloride is a solid at room temperature. Describe the separation and motion of the particles in a solid. separation ................................................................................................................................. motion .......................................................................................................................................

Sea water contains dissolved phosphate ions. State one source of phosphate ions.

Water is a simple molecular compound. Complete the dot-and-cross diagram in Fig. 2.2 for a molecule of water. Show outer electrons only.

Petroleum is a mixture of hydrocarbons and is separated by fractional distillation in an industrial process. State which physical property of hydrocarbons allows them to be separated by fractional distillation.

Describe how petroleum is separated into fractions by fractional distillation.

Name the process that breaks down long chain hydrocarbon molecules to form short chain hydrocarbon molecules.

Some of the fractions obtained from petroleum are shown. Draw a line from each fraction to its use.

Ethanoic acid is an organic molecule. Draw the displayed formula of a molecule of ethanoic acid.

Ethanoic acid reacts with sodium carbonate. Name the salt produced in this reaction.

Ethane is burned in excess oxygen. Name the two products of this process. ................................................................... and ...................................................................

Ethanol is another organic molecule. State two ways to manufacture ethanol. 1 ................................................................................................................................................ 2 ................................................................................................................................................

Fig. 3.1 shows the displayed formula of an organic molecule. Deduce the molecular formula of the molecule in Fig. 3.1.

Explain why the molecule in Fig. 3.1 is unsaturated.

Explain why nitrogen is in Group V of the Periodic Table.

Two isotopes of nitrogen are shown in Fig. 4.1. ${}_7^{14}\mathrm{N}$ ${}_7^{15}\mathrm{N}$ Fig. 4.1 Complete Table 4.1 to show the number of protons, neutrons and electrons in one atom of these isotopes.

Oxides of nitrogen are air pollutants. State one source of oxides of nitrogen in the air.

Ammonia reacts with oxygen to form nitrogen dioxide and water. Complete the symbol equation for this reaction. $$4{\mathrm{N}\mathrm{H}}_3+7{\mathrm{O}}_2\to 4{\mathrm{N}\mathrm{O}}_2+\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}{\mathrm{H}}_2\mathrm{O}$$

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

State whether nitrogen dioxide is an acidic or basic oxide. Give a reason for your answer.

A compound of nitrogen has the formula $\mathrm{A}\mathrm{l}({\mathrm{N}\mathrm{O}}_3{)}_3$. Complete Table 4.2 to calculate the relative formula mass of $\mathrm{A}\mathrm{l}({\mathrm{N}\mathrm{O}}_3{)}_3$. Table 4.2 relative formula mass = ..............................

Complete the word equation to show the reaction between copper(II) carbonate and nitric acid.

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

Fig. 5.1 shows the apparatus for the electrolysis of molten cobalt(II) bromide using inert electrodes. Label Fig. 5.1 to show the: • anode • electrolyte.

Name the products formed at the positive and negative electrodes. positive electrode .............................................................................................................. negative electrode .............................................................................................................

Table 5.1 shows some properties of five compounds, A, B, C, D and E. Table 5.1 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 ....................................................................................................................................

Tick (✓) one box that shows a chemical change. boiling ethanol decomposing vegetation dissolving salt mixing ink and water

Table 6.1 shows the results of four experiments. Table 6.1 State which experiment shows the greatest temperature change.

State which experiment is the most endothermic.

Fig. 6.1 shows an incomplete reaction pathway diagram for an exothermic reaction. Complete Fig. 6.1 by labelling: • the vertical axis • the reactants • the products.

Water needs to be treated to make it safe to drink. Complete Fig. 7.1 to show the three stages needed in the treatment of domestic water. The second stage has been completed.

Describe a chemical test for the presence of water. test ............................................................................................................................................ observations .............................................................................................................................

A sample of air contains carbon dioxide and oxides of nitrogen. State one harmful effect of each of these air pollutants. carbon dioxide .......................................................................................................................... oxides of nitrogen .....................................................................................................................

A student investigates the reaction of four different metals, A, B, C and D, with dilute sulfuric acid. All other conditions are the same. The results of the experiments are shown in Table 8.1. Table 8.1 Put the metals, A, B, C and D, in order of their reactivity. most reactive .............................. .............................. .............................. least reactive ..............................

Increasing the temperature of the acid increases the rate of reaction. State two other ways to increase the rate of this reaction. 1 ........................................................................................................................................ 2 ........................................................................................................................................

In another experiment, a student adds lithium to water. An alkaline solution is formed. State the colour seen in the flame test for lithium ions.

State the ion that all aqueous alkalis contain.

State the colour of thymolphthalein in an aqueous alkali.

Pewter is an alloy that contains tin. State which one of these diagrams, A, B, C or D, best represents an alloy.

Suggest one property of pewter that makes it more useful than pure tin.

Metals are good thermal conductors. Describe two other physical properties that are typical of metals. 1 ................................................................................................................................................ 2 ................................................................................................................................................