O Level Chemistry 5070 Paper 12, May/June 2024

Which physical changes are both exothermic? A condensation and evaporation B evaporation and melting C freezing and condensation D melting and freezing

What is tap water? A a compound B a mixture of compounds and elements C a mixture of elements D an element

In which pair of particles is: $\bullet$ the sum of their charges equal to zero $\bullet$ the sum of their masses almost the same as $\frac{1}{12}$ of the mass of an atom of ${}^{12}\mathrm{C}$? A one electron and one neutron B one electron and one proton C one neutron and one proton D two neutrons

An element has two isotopes of relative isotopic masses $x$ and $x+2$. The diagram shows the composition of atoms in a sample of the element. What is the relative atomic mass of the sample of the element? A $x+0.5$ B $x+1.0$ C $x+1.5$ D $x+2.0$

Which molecule has only four electrons involved in covalent bonds? A ${\mathrm{C}\mathrm{l}}_2$ B ${\mathrm{C}\mathrm{O}}_2$ C ${\mathrm{H}}_2\mathrm{S}$ D ${\mathrm{N}}_2$

The melting points and boiling points of four compounds, W, X, Y and Z, are given in the table.

The four compounds are silicon(IV) oxide, ethane, bromine and a carboxylic acid of formula ${\mathrm{C}}_{16}{\mathrm{H}}_{32}{\mathrm{O}}_2$. Which row identifies W, X, Y and Z?

What is the formula of zinc oxide? A ${\mathrm{Z}\mathrm{n}}_2\mathrm{O}$ B $\mathrm{Z}\mathrm{n}\mathrm{O}$ C ${\mathrm{Z}\mathrm{n}}_2{\mathrm{O}}_3$ D ${\mathrm{Z}\mathrm{n}\mathrm{O}}_2$

Which statement is correct? A If the relative formula mass of hydrated sodium carbonate, ${\mathrm{N}\mathrm{a}}_2{\mathrm{C}\mathrm{O}}_3\cdot x{\mathrm{H}}_2\mathrm{O}$, is 286, then $x$ is 10. B Phosphoric(V) acid, ${\mathrm{H}}_3{\mathrm{P}\mathrm{O}}_4$, has a relative molecular mass of 50. C The relative atomic mass of a sample of an element with isotopes of masses 20 and 22 can only be equal to 21. D The relative atomic mass of an element is the average mass of atoms of isotopes of the element compared with the mass of a hydrogen atom.

In a volumetric experiment, $25.0{\mathrm{c}\mathrm{m}}^3$ of $0.100\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}{\mathrm{d}\mathrm{m}}^3$ sodium hydroxide reacts exactly with $20.0{\mathrm{c}\mathrm{m}}^3$ of dilute sulfuric acid. $$2\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}+{\mathrm{H}}_2{\mathrm{S}\mathrm{O}}_4\to {\mathrm{N}\mathrm{a}}_2{\mathrm{S}\mathrm{O}}_4+2{\mathrm{H}}_2\mathrm{O}$$ What is the concentration of the dilute sulfuric acid? A $0.0625\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}{\mathrm{d}\mathrm{m}}^3$ B $0.0800\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}{\mathrm{d}\mathrm{m}}^3$ C $0.125\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}{\mathrm{d}\mathrm{m}}^3$ D $0.250\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{/}{\mathrm{d}\mathrm{m}}^3$

The equation for the reaction between ammonium chloride and calcium hydroxide is shown. $$2{\mathrm{N}\mathrm{H}}_4\mathrm{C}\mathrm{l}+{\mathrm{C}\mathrm{a}(\mathrm{O}\mathrm{H})}_2\to 2{\mathrm{N}\mathrm{H}}_3+{\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{l}}_2+2{\mathrm{H}}_2\mathrm{O}$$ $10.7\mathrm{g}$ of ammonium chloride and $14.8\mathrm{g}$ of calcium hydroxide are mixed and warmed. $10.0\mathrm{g}$ of calcium chloride is obtained from the reaction. What is the percentage yield of calcium chloride? [$M_{\mathrm{r}}$: ${\mathrm{N}\mathrm{H}}_4\mathrm{C}\mathrm{l}$, 53.5; ${\mathrm{C}\mathrm{a}(\mathrm{O}\mathrm{H})}_2$, 74; ${\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{l}}_2$, 111] A 39.2% B 45.0% C 67.6% D 90.1%

The diagram shows a simple electrolytic cell. Which arrows show the movement of electrons? A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 2 only

Which changes are observed during the electrolysis of aqueous copper(II) sulfate using copper electrodes? 1 A pink solid is deposited on the negative electrode. 2 Bubbles form on the positive electrode. 3 The colour of the solution does not change. A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 2 and 3 only

Which row describes a hydrogen-oxygen fuel cell?

Which statements about endothermic reactions are correct? 1 Energy is absorbed from the surroundings. 2 Energy is released to the surroundings. 3 The temperature of the reaction mixture falls. 4 The temperature of the reaction mixture rises. A 1 and 3 B 1 and 4 C 2 and 3 D 2 and 4

Hydrogen and chlorine react to form hydrogen chloride. $${\mathrm{H}}_2+{\mathrm{C}\mathrm{l}}_2\to 2\mathrm{H}\mathrm{C}\mathrm{l}$$ Bond energy data is given in the table.

What is the enthalpy change, $\mathrm{\Delta }H$, for this reaction? A $-247\mathrm{k}\mathrm{J}\mathrm{/}\mathrm{m}\mathrm{o}\mathrm{l}$ B $-184\mathrm{k}\mathrm{J}\mathrm{/}\mathrm{m}\mathrm{o}\mathrm{l}$ C $+184\mathrm{k}\mathrm{J}\mathrm{/}\mathrm{m}\mathrm{o}\mathrm{l}$ D $+247\mathrm{k}\mathrm{J}\mathrm{/}\mathrm{m}\mathrm{o}\mathrm{l}$

Which statement is correct? A Both physical changes and chemical changes produce new substances. B Chemical changes are irreversible. C During a chemical change, atoms rearrange themselves to form new chemical bonds. D The only way to reverse a physical change is with a chemical reaction.

Two reactions each produce a gaseous product. The reactions are performed separately using the same conditions of temperature and pressure. The volume of gas formed in each experiment is measured over time and the results are plotted in the graph shown. At which point is the rate of production of gas the greatest?

The reaction between calcium oxide and carbon dioxide is reversible and the forward reaction is exothermic. $$\mathrm{C}\mathrm{a}\mathrm{O}(\mathrm{s})+{\mathrm{C}\mathrm{O}}_2(\mathrm{g})\rightleftharpoons {\mathrm{C}\mathrm{a}\mathrm{C}\mathrm{O}}_3(\mathrm{s})$$ A mixture of calcium oxide and carbon dioxide is placed in a heated flask and the reaction reaches equilibrium. Which statement about this equilibrium is correct? A Less calcium carbonate is produced if the pressure in the flask increases. B More calcium carbonate is produced when the temperature is increased. C The flask must be sealed if equilibrium is to be reached. D When equilibrium is reached, the reaction stops.

In the Haber process, hydrogen and nitrogen react to form ammonia in the presence of a catalyst. Which reactant is obtained by fractional distillation and what is the catalyst used in the Haber process?

Chlorine reacts with aqueous sodium bromide to form aqueous sodium chloride and bromine. Which statement about this reaction is correct? A Bromide ions are oxidised because they lose electrons. B Chlorine atoms are oxidised because they gain electrons. C Sodium ions are oxidised because they lose electrons. D This reaction does not involve oxidation or reduction.

One mole of compound X gives two moles of ions in aqueous solution. X reacts with ammonium carbonate to give an acidic gas. What is compound X? A calcium hydroxide B ethanoic acid C nitric acid D sodium hydroxide

Which statement about weak acids is correct? A Some molecules are not dissociated. B Weak acids do not react with carbonates. C Weak acids always form more dilute solutions than strong acids. D Weak acids always have lower pH values than strong acids.

Which compound is the least soluble in water? A calcium chloride B lead nitrate C magnesium carbonate D potassium sulfate

Which statement about water of crystallisation is correct? A The ratio of ${\mathrm{C}\mathrm{o}\mathrm{C}\mathrm{l}}_2:{\mathrm{H}}_2\mathrm{O}$ in hydrated cobalt(II) chloride is $6:1$. B The ratio of ${\mathrm{C}\mathrm{u}\mathrm{S}\mathrm{O}}_4:{\mathrm{H}}_2\mathrm{O}$ in hydrated copper(II) sulfate is $1:5$. C When a saturated solution is heated, the water that evaporates is called the water of crystallisation. D When white copper(II) sulfate is heated, blue crystals are formed.

The diagram shows a section of the Periodic Table. Which element is a metal that has exactly three outer shell electrons?

The table compares two properties of lithium and potassium. Which row is correct?

Which properties are correct for the element copper?

Which statement is correct? A Copper is unreactive because of an oxide layer. B Gold and silver are used to make jewellery because they corrode very slowly. C Magnesium can be displaced from aqueous solutions of its ions by adding aluminium. D Zinc gains electrons more readily than magnesium gains electrons.

Which reaction takes place in the blast furnace? A ${\mathrm{F}\mathrm{e}\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_4+4\mathrm{C}\to \mathrm{F}\mathrm{e}+2\mathrm{C}\mathrm{r}+4\mathrm{C}\mathrm{O}$ B $3\mathrm{F}\mathrm{e}+4{\mathrm{H}}_2\mathrm{O}\to {\mathrm{F}\mathrm{e}}_3{\mathrm{O}}_4+4{\mathrm{H}}_2$ C ${\mathrm{S}\mathrm{i}\mathrm{O}}_2+\mathrm{C}\mathrm{a}\mathrm{O}\to {\mathrm{C}\mathrm{a}\mathrm{S}\mathrm{i}\mathrm{O}}_3$ D ${\mathrm{S}\mathrm{i}\mathrm{O}}_2+2\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}\to {\mathrm{N}\mathrm{a}}_2{\mathrm{S}\mathrm{i}\mathrm{O}}_3+{\mathrm{H}}_2\mathrm{O}$

The presence of water can be confirmed by the use of either anhydrous cobalt(II) chloride or anhydrous copper(II) sulfate. Which observation is correct if water is present? A Anhydrous cobalt(II) chloride turns from blue to white. B Anhydrous cobalt(II) chloride turns from pink to blue. C Anhydrous copper(II) sulfate turns from blue to pink. D Anhydrous copper(II) sulfate turns from white to blue.

Ammonium phosphate, $({\mathrm{N}\mathrm{H}}_4{)}_3{\mathrm{P}\mathrm{O}}_4$, may be used as a fertiliser. What is the percentage by mass of elements that improve plant growth in ammonium phosphate? A 9 B 21 C 28 D 49

Which statement is correct? A An unsaturated hydrocarbon is one in which more solute can dissolve. B Members of a homologous series each differ from the next by a $-{\mathrm{C}\mathrm{H}}_2-$ unit. C Structural isomers have the same displayed formula but different structural formulae. D The general formula of the carboxylic acid homologous series is ${\mathrm{C}}_n{\mathrm{H}}_{2n}\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$.

What is the name of the ester ${\mathrm{C}}_3{\mathrm{H}}_7{\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{C}}_2{\mathrm{H}}_5$? A butyl ethanoate B ethyl butanoate C ethyl propanoate D propyl ethanoate

Petroleum is separated into useful products by fractional distillation. Which of these fractions has the lowest boiling point? A bitumen B fuel oil C gasoline / petrol D kerosene / paraffin

Which equation represents a substitution reaction? A ${\mathrm{C}}_3{\mathrm{H}}_8+{\mathrm{C}\mathrm{l}}_2\to {\mathrm{C}}_3{\mathrm{H}}_7\mathrm{C}\mathrm{l}+\mathrm{H}\mathrm{C}\mathrm{l}$ B ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{O}\mathrm{H}+3{\mathrm{O}}_2\to 2{\mathrm{C}\mathrm{O}}_2+3{\mathrm{H}}_2\mathrm{O}$ C ${\mathrm{C}}_2{\mathrm{H}}_4+{\mathrm{B}\mathrm{r}}_2\to {\mathrm{C}}_2{\mathrm{H}}_4{\mathrm{B}\mathrm{r}}_2$ D ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\to 2{\mathrm{C}\mathrm{O}}_2+2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{O}\mathrm{H}$

Which row shows the minimum number of moles of oxygen needed for the complete combustion of 1 mole of the named alcohol?

The diagram shows the partial structure of a polymer. Which pair of reagents is used to form this polymer?

A student measures the rate at which a fixed mass of magnesium reacts with a fixed volume of dilute hydrochloric acid. Which additional pieces of apparatus are required for this experiment? A a balance, a measuring cylinder and a stop-watch only B a balance, a measuring cylinder and a thermometer only C a balance, a stop-watch and a thermometer only D a measuring cylinder, a stop-watch and a thermometer only

Two titrations of dilute hydrochloric acid with aqueous sodium hydroxide are done using two different indicators, methyl orange and thymolphthalein. The equation for the reaction is shown. $$\mathrm{H}\mathrm{C}\mathrm{l}(\mathrm{a}\mathrm{q})+\mathrm{N}\mathrm{a}\mathrm{O}\mathrm{H}(\mathrm{a}\mathrm{q})\to \mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}(\mathrm{a}\mathrm{q})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$$ Using a volumetric pipette, $25.0{\mathrm{c}\mathrm{m}}^3$ dilute hydrochloric acid is added to a conical flask with a few drops of indicator. Aqueous sodium hydroxide is added from a burette to the dilute hydrochloric acid until the end-point is reached. The end-point of the titration with each indicator occurs when $23.6{\mathrm{c}\mathrm{m}}^3$ of aqueous sodium hydroxide is added. Which statements about this experiment are correct? 1 The methyl orange changes colour from red to yellow. 2 The thymolphthalein changes colour from blue to colourless. 3 The dilute hydrochloric acid is less concentrated than the aqueous sodium hydroxide. A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 2 and 3 only

What is used to separate a solid mixture of copper powder and sodium chloride to obtain pure, solid samples of each compound? 1 a suitable solvent 2 distillation 3 crystallisation 4 filtration A 1, 2 and 4 B 1 and 2 only C 1, 3 and 4 D 3 and 4 only