O Level Chemistry 5070 Paper 22, Oct/Nov 2025

State which compound: is methanoic acid

State which compound: is manufactured by the hydration of ethene

State which compound: has an empirical formula of ${\mathrm{C}}_2{\mathrm{H}}_4\mathrm{O}$

State which compound: is used to make an addition polymer

State which compound: is an ester.

State which two compounds are structural isomers of one another.

Describe one difference between the isotopes ${}_{22}^{46}\mathrm{T}\mathrm{i}$ and ${}_{22}^{47}\mathrm{T}\mathrm{i}$.

Explain why all the isotopes of titanium have the same chemical properties.

Show by calculation that the relative atomic mass of titanium for this sample is 47.84.

Fig. 3.1 shows the reaction pathway diagram for this reaction. Identify the energy changes labelled A and B. energy change A energy change B

Use the reaction pathway diagram to explain why the reaction is exothermic.

Describe a chemical test for hydrogen. test observation if hydrogen present

A sample of aluminium reacts completely with dilute hydrochloric acid. A total volume of $366{\mathrm{c}\mathrm{m}}^3$ of hydrogen, measured at r.t.p., is produced. Calculate the mass of the sample of aluminium. Give your answer to two significant figures. mass of aluminium = ...................................................... g

Fluorine has a low boiling point. It is a gas at room temperature. Describe the arrangement and motion of molecules in fluorine gas.

Explain why fluorine is a gas at room temperature. Use ideas about structure and bonding.

Bromine reacts with lithium to make the ionic compound lithium bromide. Suggest two physical properties of lithium bromide. 1 2

Construct the ionic half-equation to show the formation of lithium ions from lithium atoms.

Construct the ionic half-equation to show the formation of bromide ions from bromine molecules.

Chlorine gas is bubbled into aqueous lithium bromide. A reaction takes place. Name the two products of this reaction.

One of the properties of nickel is that it is a catalyst. State a reaction that uses nickel as a catalyst.

State one other chemical property of nickel that is typical of a transition element.

The physical properties of nickel and its alloys can be explained using ideas about structure and bonding. Explain why nickel is malleable.

Nickel and other elements are added to iron to make the alloy stainless steel. Explain why stainless steel is harder than either pure nickel or pure iron. Include a labelled diagram in your answer.

Stainless steel is used to make cutlery because it is hard and strong. State one other property that makes stainless steel suitable to make cutlery.

Compound X contains nickel, hydrogen and oxygen only. X contains 2.2% by mass of hydrogen and 34.5% by mass of oxygen. Calculate the empirical formula of compound X. empirical formula =

The equation for the reversible reaction between carbon monoxide and nickel is shown. $$4\mathrm{C}\mathrm{O}(\mathrm{g})+\mathrm{N}\mathrm{i}(\mathrm{s})\rightleftharpoons \mathrm{N}\mathrm{i}(\mathrm{C}\mathrm{O}{)}_4(\mathrm{g})$$ The forward reaction is exothermic. The reversible reaction is allowed to reach equilibrium in a closed system. Predict and explain the effect of increasing the pressure on the position of equilibrium. The temperature remains constant. prediction explanation

Draw the dot-and-cross diagram to show the electronic arrangement in a molecule of hydrogen peroxide. Only draw the outer shell electrons of oxygen and hydrogen.

A sample of hydrogen peroxide has a mass of $0.170\mathrm{g}$. Calculate the number of molecules of hydrogen peroxide in this sample. One mole of hydrogen peroxide contains $6.02\times {10}^{23}$ molecules. number of molecules =

Calculate the total number of atoms in this sample of hydrogen peroxide. number of atoms =

When aqueous hydrogen peroxide reacts with acidified aqueous potassium manganate(VII) there is a colour change from purple to colourless. When aqueous hydrogen peroxide reacts with aqueous potassium iodide there is a colour change from colourless to brown. Explain what these observations indicate about the chemical properties of aqueous hydrogen peroxide.

Barium peroxide reacts with cold dilute sulfuric acid to produce hydrogen peroxide. Barium peroxide contains the ions ${\mathrm{B}\mathrm{a}}^{2+}$ and ${\mathrm{O}}_2^{2-}$ only. Deduce the formula of barium peroxide.

The equation for the decomposition of aqueous hydrogen peroxide is shown. $$2{\mathrm{H}}_2{\mathrm{O}}_2(\mathrm{a}\mathrm{q})\to 2{\mathrm{H}}_2\mathrm{O}(\mathrm{l})+{\mathrm{O}}_2(\mathrm{g})$$ The rate of decomposition increases as the temperature of the aqueous hydrogen peroxide increases. Explain why.

Manganese(IV) oxide is a catalyst for the decomposition of aqueous hydrogen peroxide. Describe how a catalyst increases the rate of reaction.

Name the two types of monomer shown in Fig. 7.1. 1 2

The two monomers react to make PET and a small molecule. Name the small molecule.

Draw the structure of PET. Your structure should show two repeat units.

State two environmental challenges caused by the disposal of plastics made of PET. 1 2

Name one condensation polymer that is a polyamide.

Explain why X is unsaturated.

Describe the observations when X reacts with aqueous bromine.

X is a weak acid. Describe the meaning of the term weak in weak acid.

X reacts with aqueous sodium carbonate. Name the gas formed in this reaction.

Describe how an ester is prepared from X.

Ethanoic acid is a saturated carboxylic acid. Describe how ethanoic acid is made from ethanol.

Dilute ethanoic acid reacts with aqueous sodium hydroxide. Name the two products of this reaction.

State the meaning of the term hydrated.

Aqueous ammonia is added dropwise until in excess to a small volume of aqueous zinc chloride. Describe the observations during this addition.

Describe the observations when aqueous silver nitrate is added to aqueous zinc chloride.

Dilute and concentrated aqueous zinc chloride are electrolysed separately using carbon electrodes. Complete Table 9.1. Table 9.1

Explain why aqueous zinc chloride conducts electricity but solid zinc chloride does not conduct electricity.

Rivers and lakes are natural sources of water. Name one substance in river water that may be harmful. Explain why this substance may be harmful. substance explanation

Name one substance in river water that is beneficial. Explain why this substance is beneficial. substance explanation

Describe the three processes involved in the treatment of water for the domestic water supply. State the reason why each process is used. process 1 reason process 2 reason process 3 reason

Describe a qualitative chemical test to show the presence of water. chemical test observation

Explain how the purity of water is tested by measuring its boiling point.