IGCSE Chemistry 0620 Paper 31, May/June 2023

forms 78% by volume of clean, dry air

has an atom with a complete outer electron shell

has an atom with five occupied electron shells

forms an ion with a charge of 2–

forms an ion that gives a green precipitate on addition of aqueous sodium hydroxide

is used in food containers because of its resistance to corrosion.

Table 2.1 shows some properties of the halogens. Table 2.1 Use the information in Table 2.1 to predict: the melting point of bromine

the density of iodine at room temperature and pressure

the physical state of chlorine at –10°C. Give a reason for your answer. physical state ...................................................................................................................... reason ................................................................................................................................. .............................................................................................................................................

The equation for the reaction of aqueous chlorine with aqueous potassium iodide is shown. $${\text{Cl}}_2+2\text{KI}\to {\text{I}}_2+2\text{KCl}$$ Choose the word which best describes this type of chemical reaction. Draw a circle around your chosen answer. addition displacement neutralisation polymerisation

Explain why aqueous iodine does not react with aqueous potassium chloride.

Complete the diagram in Fig. 2.1 to show the electronic configuration of a chlorine atom.

Describe a test for chlorine. test ............................................................................................................................................. observations ..............................................................................................................................

Water from natural sources contains dissolved gases. Choose from the list, the gas that is essential for aquatic life. Draw a circle around your chosen answer. argon hydrogen nitrogen oxygen

Polluted water may contain harmful substances such as metal compounds, plastics, nitrates and phosphates. Name one other harmful substance which is present in polluted water.

State why nitrates are harmful to aquatic life.

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

State the name of the ${\text{NH}}_4^{+}$ ion.

Calculate the mass of calcium ions present in $200{\text{ cm}}^3$ of polluted water. mass = .............................. mg

Copper(II) sulfate can be used to test for the presence of water. $${\text{CuSO}}_4(\text{s})+5{\text{H}}_2\text{O}(\text{l})\rightleftharpoons {\text{CuSO}}_4\cdot 5{\text{H}}_2\text{O}(\text{s})$$ State the meaning of the term hydrated.

Describe how hydrated copper(II) sulfate is changed to anhydrous copper(II) sulfate.

Complete the symbol equation for the reaction of sodium with water. $$2\text{Na}+\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}{\text{H}}_2\text{O}\to 2\text{NaOH}+\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}\mathrm{.}$$

Sulfur has several isotopes. Define the term isotopes.

Deduce the number of protons, neutrons and electrons in the sulfide ion shown. $${}_{16}^{36}{\text{S}}^{2-}$$ number of protons ..................................................................................................................... number of neutrons ................................................................................................................... number of electrons ...................................................................................................................

Sulfur burns in oxygen to produce sulfur dioxide. Fig. 4.1 shows an incomplete reaction pathway diagram for this reaction. Complete Fig. 4.1 by writing these formulae on the diagram: ● $\text{S}+{\text{O}}_2$ ● ${\text{SO}}_2$.

Explain how Fig. 4.1 shows that the reaction is exothermic.

Complete this sentence about an exothermic reaction using a word from the list. products reactants sulfur surroundings An exothermic reaction transfers thermal energy to the ............................. .

Fig. 4.2 shows the apparatus used for the electrolysis of dilute sulfuric acid using graphite electrodes. Label Fig. 4.2 to show: ● the cathode ● the electrolyte.

Name the products and state the observations at the positive and negative electrodes. product at the positive electrode ............................................................................................................................................. observations at the positive electrode ............................................................................................................................................. product at the negative electrode ............................................................................................................................................. observations at the negative electrode .............................................................................................................................................

Complete the word equation for the reaction of dilute sulfuric acid with sodium carbonate.

A few drops of thymolphthalein indicator are added to dilute sulfuric acid. State the colour of the solution.

Iron is a transition element. Potassium is an element in Group I of the Periodic Table. State two differences in the physical properties of iron compared to potassium. 1 ................................................................................................................................................. 2 .................................................................................................................................................

Carbon is used to extract iron from iron ore in a blast furnace. State two uses of carbon in the extraction process. 1 ................................................................................................................................................. 2 .................................................................................................................................................

Steel is an alloy of iron. State the meaning of the term alloy.

State why alloys are more useful than pure metals.

Table 5.1 shows the observations made when four different metals react with dilute hydrochloric acid of the same concentration. Table 5.1 Put the four metals in order of their reactivity. Put the least reactive metal first.

A student investigates the reaction of small pieces of zinc of the same mass and size with three different concentrations of dilute hydrochloric acid in the presence of a catalyst. The three concentrations of dilute hydrochloric acid are: ● $1.0\text{ mol}\mathrm{/}{\text{dm}}^3$ ● $1.5\text{ mol}\mathrm{/}{\text{dm}}^3$ ● $2.0\text{ mol}\mathrm{/}{\text{dm}}^3$. All other conditions stay the same. Table 6.1 shows the time taken for each reaction to finish. Complete Table 6.1 by writing the concentrations of hydrochloric acid in the first column.

Describe the effect on the time taken for the zinc to finish reacting with $2.0\text{ mol}\mathrm{/}{\text{dm}}^3$ hydrochloric acid with no catalyst present. All other conditions stay the same.

Describe the effect on the time taken for the zinc to finish reacting with $2.0\text{ mol}\mathrm{/}{\text{dm}}^3$ hydrochloric acid when the surface area of the zinc is increased. All other conditions stay the same.

Crystals of zinc chloride can be prepared by reacting excess zinc with dilute hydrochloric acid. Choose from the list, the method used to separate the unreacted zinc from the reaction mixture. Draw a circle around your chosen answer. chromatography crystallisation evaporation filtration

Zinc chloride is soluble in water. Choose one other compound that is soluble in water. Tick (✓) one box. calcium carbonate lead(II) chloride silver chloride sodium nitrate

Fig. 7.1 shows the displayed formula of mesaconic acid. On Fig. 7.1 draw a circle around one carboxylic acid functional group.

Deduce the molecular formula of mesaconic acid.

Mesaconic acid is a colourless compound. Describe the colour change when excess mesaconic acid is added to aqueous bromine. from ............................................................ to ............................................................

Ethanoic acid belongs to the homologous series of carboxylic acids. Define the term homologous series.

Complete the word equation for the reaction of ethanoic acid with magnesium.

Ethanoic acid reacts with ethanol. The organic product has the molecular formula ${\text{C}}_4{\text{H}}_8{\text{O}}_2$. Complete Table 7.1 to calculate the relative molecular mass of ${\text{C}}_4{\text{H}}_8{\text{O}}_2$. Table 7.1 relative molecular mass = ..............................

Ethanol can be manufactured by fermentation. Complete the word equation for one other method of manufacturing ethanol. ................................ + ................................ → ethanol

Nitrogen is a non-metal. Nitrogen is a poor electrical conductor. Describe two other physical properties which are typical of non-metals. 1 ................................................................................................................................................. 2 .................................................................................................................................................

Oxides of nitrogen are air pollutants which contribute to acid rain. State one source of oxides of nitrogen in the air.

State one other adverse effect of oxides of nitrogen.

Ammonia is a simple molecule with covalent bonds. Describe a covalent bond.

Complete Fig. 8.1 to show the dot-and-cross diagram for a molecule of ammonia. Show outer shell electrons only.

Aqueous ammonia is alkaline. Choose from the list, the pH value that is alkaline. Draw a circle around your chosen answer. pH 1 pH 5 pH 7 pH 10

Aqueous ammonia releases ammonia gas. Ammonia gas turns damp red litmus paper blue. A long glass tube is set up as shown in Fig. 8.2. At first, the litmus paper does not turn blue. After a short time, the litmus paper turns blue. Explain these results in terms of the kinetic particle theory.