IGCSE Chemistry 0620 Paper 21, May/June 2023

The diagram shows the result of dropping a purple crystal into water. Which processes take place in this experiment? A chemical reaction: ✓, diffusing: ✓, dissolving: ✗ B chemical reaction: ✓, diffusing: ✗, dissolving: ✗ C chemical reaction: ✗, diffusing: ✗, dissolving: ✓ D chemical reaction: ✗, diffusing: ✓, dissolving: ✓

Which row about elements, mixtures and compounds is correct? A metallic element: copper, non-metallic element: methane, mixture: brass, compound: sulfur B metallic element: brass, non-metallic element: sulfur, mixture: copper, compound: methane C metallic element: copper, non-metallic element: sulfur, mixture: brass, compound: methane D metallic element: brass, non-metallic element: methane, mixture: copper, compound: sulfur

The atomic structures of four particles, W, X, Y and Z, are shown. W: 2 electrons, 2 neutrons, 2 protons X: 2 electrons, 2 neutrons, 3 protons Y: 2 electrons, 3 neutrons, 2 protons Z: 3 electrons, 2 neutrons, 3 protons Which particles are isotopes of the same element? A W and X B W and Y C X and Y D X and Z

Which statement explains why isotopes of the same element have the same chemical properties? A They have the same number of outer shell electrons. B They have the same number of neutrons. C They have different numbers of protons. D They have different mass numbers.

Nitrogen forms a nitride ion with the formula ${\mathrm{N}}^{3-}$. Which particle does not have the same electronic configuration as the nitride ion? A ${\mathrm{A}\mathrm{l}}^{3+}$ B ${\mathrm{C}\mathrm{l}}^{-}$ C ${\mathrm{N}\mathrm{a}}^{+}$ D ${\mathrm{O}}^{2-}$

Which row describes the formation of single covalent bonds in methane? A atoms share a pair of electrons | both atoms gain a noble gas electronic structure B atoms share a pair of electrons | both atoms have the same number of electrons in their outer shell C electrons are transferred from one atom to another | both atoms gain a noble gas electronic structure D electrons are transferred from one atom to another | both atoms have the same number of electrons in their outer shell

Which formula is an empirical formula? A ${\mathrm{C}}_2{\mathrm{H}}_4\mathrm{O}$ B ${\mathrm{C}}_4{\mathrm{H}}_8{\mathrm{O}}_2$ C ${\mathrm{C}}_3{\mathrm{H}}_7\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$ D ${\mathrm{C}\mathrm{H}}_3{\mathrm{C}\mathrm{H}}_2{\mathrm{C}\mathrm{H}}_2\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{H}$

Heating iron sulfide, ${\mathrm{F}\mathrm{e}\mathrm{S}}_2$, in air produces sulfur dioxide. $$4{\mathrm{F}\mathrm{e}\mathrm{S}}_2+11{\mathrm{O}}_2\to 2{\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3+8{\mathrm{S}\mathrm{O}}_2$$ What is the maximum mass of sulfur dioxide produced from $120\text{ kg}$ of iron sulfide? A $64\text{ kg}$ B $128\text{ kg}$ C $240\text{ kg}$ D $512\text{ kg}$

Which substance produces hydrogen and bromine when electrolysed? A concentrated aqueous copper(II) bromide B concentrated aqueous sodium bromide C dilute aqueous potassium bromide D molten lead(II) bromide

Which statements about hydrogen fuel cells are correct? 1 Water is formed as the only waste product. 2 Both water and carbon dioxide are formed as waste products. 3 The overall reaction is $2{\mathrm{H}}_2+{\mathrm{O}}_2\to 2{\mathrm{H}}_2\mathrm{O}$. 4 The overall reaction is endothermic. A 1 and 3 B 1 and 4 C 2 and 3 D 2 and 4

Ethene gas, ${\mathrm{C}}_2{\mathrm{H}}_4$, is completely burned in excess oxygen to form carbon dioxide and water. The equation for this exothermic reaction is shown. $${\mathrm{C}}_2{\mathrm{H}}_4+3{\mathrm{O}}_2\to 2{\mathrm{C}\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}$$ The table shows the bond energies involved in the reaction.

What is the total energy change in this reaction? A $-954\text{ kJ}\mathrm{/}\text{mol}$ B $-1010\text{ kJ}\mathrm{/}\text{mol}$ C $-1313\text{ kJ}\mathrm{/}\text{mol}$ D $-1369\text{ kJ}\mathrm{/}\text{mol}$

Which row describes the effect on the activation energy and the frequency of particle collisions when the temperature of a chemical reaction is increased? A activation energy: increases, frequency of collisions: increases B activation energy: no change, frequency of collisions: increases C activation energy: increases, frequency of collisions: no change D activation energy: no change, frequency of collisions: no change

Solid copper(II) sulfate exists in two different forms, anhydrous and hydrated. One of these forms is blue and the other is white. The change between these two forms is reversible. $$\text{blue form}\rightleftharpoons \text{white form}$$ What is the blue form and how is the change from the blue form to the white form brought about? A blue form: anhydrous, change to white form: add water B blue form: anhydrous, change to white form: heat C blue form: hydrated, change to white form: add water D blue form: hydrated, change to white form: heat

Sodium ions, ${\mathrm{N}\mathrm{a}}^{+}$, and oxygen ions, ${\mathrm{O}}^{2-}$, combine with chromium ions to form a salt. The salt sodium dichromate has the formula ${\mathrm{N}\mathrm{a}}_2{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_7$. What is the oxidation state of chromium in this salt? A $+2$ B $+3$ C $+6$ D $+12$

The concentration of hydrogen ions in $100{\text{ cm}}^3$ of $0.1\text{ mol}\mathrm{/}{\text{dm}}^3$ hydrochloric acid is higher than the concentration of hydrogen ions in $100{\text{ cm}}^3$ of $0.1\text{ mol}\mathrm{/}{\text{dm}}^3$ ethanoic acid. Which statement explains the difference in hydrogen ion concentration? A Ethanoic acid is an organic acid. B Ethanoic acid has a lower pH than hydrochloric acid. C Ethanoic acid is partially dissociated. D Ethanoic acid is a strong acid.

Which oxide is classified as an amphoteric oxide? A aluminium oxide B calcium oxide C copper(II) oxide D nitrogen oxide

Which method produces the salt copper(II) carbonate? A Add copper(II) oxide to water, then add excess aqueous sodium carbonate. Filter off the precipitate. B Add copper(II) oxide to dilute sulfuric acid, then add excess aqueous sodium carbonate. Filter off the precipitate. C Add copper to dilute hydrochloric acid, then add aqueous sodium carbonate. Filter off the precipitate. D Add copper(II) oxide to excess aqueous sodium carbonate. Filter off the precipitate.

Which statements about the trends across a period of the Periodic Table are correct? 1 Aluminium is more metallic than sodium. 2 Beryllium is more metallic than carbon. 3 Boron is more metallic than lithium. 4 Magnesium is more metallic than silicon. A 1 and 2 B 1 and 3 C 2 and 4 D 3 and 4

Some information about elements in Group II of the Periodic Table is shown.

Which row shows the correct trends in reactivity, density and melting point of the elements going down Group II of the Periodic Table? A reactivity: decreases down group, density: increases down group, melting point: decreases down group B reactivity: decreases down group, density: decreases down group, melting point: no clear trend C reactivity: increases down group, density: no clear trend, melting point: increases down group D reactivity: increases down group, density: no clear trend, melting point: no clear trend

A new element oxfordium, Ox, was discovered with the following properties. solubility: insoluble in water electrical conduction: does not conduct formula of element: ${\mathrm{O}\mathrm{x}}_2$ bonding in a molecule of ${\mathrm{O}\mathrm{x}}_2$: $\mathrm{O}\mathrm{x}=\mathrm{O}\mathrm{x}$ In which group of the Periodic Table should the new element be placed? A Group III B Group V C Group VII D Group VIII

Which row describes a similarity and a difference between chlorine and bromine? A similarity: both are gases at room temperature and pressure | difference: chlorine and bromine have different colours B similarity: both exist as diatomic molecules | difference: chlorine is more dense than bromine C similarity: both have atoms with seven outer-shell electrons | difference: only bromine will react with aqueous sodium chloride D similarity: both react with aqueous potassium iodide | difference: chlorine is more reactive than bromine

Which statement describes transition elements? A They have high densities and high melting points. B They have high densities and low melting points. C They have low densities and high melting points. D They have low densities and low melting points.

Which gas is made when powdered zinc is added to dilute hydrochloric acid? A carbon dioxide B chlorine C hydrogen D oxygen

The diagram represents the structure of a solid. Which solids does the diagram represent? A brass: ✓, graphite: ✓, sodium chloride: ✗ B brass: ✓, graphite: ✗, sodium chloride: ✗ C brass: ✗, graphite: ✓, sodium chloride: ✓ D brass: ✗, graphite: ✗, sodium chloride: ✓

Steel is an alloy of iron. Which statement explains why steel is stronger than iron? A Steel contains carbon which is a very hard substance. B The carbon atoms in steel bond together very strongly. C The carbon atoms in steel make the iron atoms bond together very strongly. D The carbon atoms prevent layers of iron atoms from sliding over each other.

Three students, X, Y and Z, are told that solid P reacts with dilute acids and also conducts electricity. The table shows the students' suggestions about the identity of P. X: copper Y: iron Z: graphite Which students are correct? A X, Y and Z B X only C Y only D Z only

Which statement explains why aluminium appears to be unreactive? A It is coated in an oxide layer. B It has a low density. C It is low in the reactivity series. D It is solid at room temperature.

During the electrolysis of aluminium oxide, the mass of the carbon anode changes. Which row describes the change and gives a reason for this change? A mass change of the anode: decreases | reason: carbon reacts to form carbon dioxide B mass change of the anode: decreases | reason: carbon dissolves in molten cryolite C mass change of the anode: increases | reason: electrodes become coated with cryolite D mass change of the anode: increases | reason: electrodes become coated with aluminium

Several processes are used to treat domestic water. Which row identifies a reason for the given process? A process: chlorination | reason: removes impurities B process: filtration | reason: removes insoluble solids C process: sedimentation | reason: removes soluble solids D process: use of carbon | reason: kills bacteria

What is the equation for photosynthesis? A ${\mathrm{C}\mathrm{O}}_2+3{\mathrm{H}}_2\to {\mathrm{C}\mathrm{H}}_3\mathrm{O}\mathrm{H}+{\mathrm{H}}_2\mathrm{O}$ B $6{\mathrm{C}\mathrm{O}}_2+6{\mathrm{H}}_2\mathrm{O}\to {\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+6{\mathrm{O}}_2$ C ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6\to 2{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{O}\mathrm{H}+2{\mathrm{C}\mathrm{O}}_2$ D ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+6{\mathrm{O}}_2\to 6{\mathrm{C}\mathrm{O}}_2+6{\mathrm{H}}_2\mathrm{O}$

Which statement describes how the $\mathrm{C}-\mathrm{H}$ bonds in methane gas in the atmosphere contribute to global warming? A They absorb thermal energy from the Sun and emit some of this energy into space. B They absorb thermal energy from the Sun and emit all of this energy towards the Earth. C They absorb thermal energy from the Earth and emit all of this energy towards the Earth. D They absorb thermal energy from the Earth and emit some of this energy towards the Earth.

The structural formulae of two hydrocarbons are shown. $${\mathrm{C}\mathrm{H}}_3{\mathrm{C}\mathrm{H}}_2{\mathrm{C}\mathrm{H}}_2{\mathrm{C}\mathrm{H}}_3{\mathrm{C}\mathrm{H}}_3\mathrm{C}\mathrm{H}({\mathrm{C}\mathrm{H}}_3){\mathrm{C}\mathrm{H}}_3$$ Which statement about the hydrocarbons is correct? A They are both alkenes. B They decolourise aqueous bromine. C They are structural isomers. D They undergo addition reactions.

The structural formula of compound Q is given. $${\mathrm{C}\mathrm{H}}_3{\mathrm{C}\mathrm{H}}_2{\mathrm{C}\mathrm{H}}_2{\mathrm{C}\mathrm{O}\mathrm{O}\mathrm{C}\mathrm{H}}_2{\mathrm{C}\mathrm{H}}_2{\mathrm{C}\mathrm{H}}_3$$ What is compound Q? A butyl butanoate B butyl propanoate C propyl butanoate D propyl propanoate

The fractional distillation of petroleum is shown. Which fraction contains hydrocarbons with the longest chain length? A B C D

Which equation represents the cracking of an alkane? A $3{\mathrm{C}}_2{\mathrm{H}}_4\to {\mathrm{C}}_6{\mathrm{H}}_{12}$ B ${\mathrm{C}}_6{\mathrm{H}}_{12}+{\mathrm{H}}_2\to {\mathrm{C}}_6{\mathrm{H}}_{14}$ C ${\mathrm{C}}_6{\mathrm{H}}_{14}\to 6\mathrm{C}+7{\mathrm{H}}_2$ D ${\mathrm{C}}_6{\mathrm{H}}_{14}\to {\mathrm{C}}_2{\mathrm{H}}_4+{\mathrm{C}}_4{\mathrm{H}}_{10}$

What is the structure of the product of the reaction of propene with bromine? A ${\mathrm{C}\mathrm{H}}_3{\mathrm{C}\mathrm{H}}_2{\mathrm{C}\mathrm{H}}_2\mathrm{B}\mathrm{r}$ B ${\mathrm{C}\mathrm{H}}_3\mathrm{C}(\mathrm{B}\mathrm{r})=\mathrm{C}\mathrm{H}\mathrm{B}\mathrm{r}$ C ${\mathrm{C}\mathrm{H}}_3{\mathrm{C}\mathrm{H}\mathrm{B}\mathrm{r}\mathrm{C}\mathrm{H}}_2\mathrm{B}\mathrm{r}$ D ${\mathrm{C}\mathrm{H}}_2{\mathrm{B}\mathrm{r}\mathrm{C}\mathrm{H}}_2{\mathrm{C}\mathrm{H}}_2\mathrm{B}\mathrm{r}$

In reaction R, 2000 molecules of ${\mathrm{C}\mathrm{H}}_2={\mathrm{C}\mathrm{H}}_2$ react to form a single molecule X only. $$2000{\mathrm{C}\mathrm{H}}_2={\mathrm{C}\mathrm{H}}_2\to \mathrm{X}$$ Which terms describe reaction R, ${\mathrm{C}\mathrm{H}}_2={\mathrm{C}\mathrm{H}}_2$ and X? A reaction R: addition, ${\mathrm{C}\mathrm{H}}_2={\mathrm{C}\mathrm{H}}_2$: monomer, X: polymer B reaction R: addition, ${\mathrm{C}\mathrm{H}}_2={\mathrm{C}\mathrm{H}}_2$: polymer, X: monomer C reaction R: substitution, ${\mathrm{C}\mathrm{H}}_2={\mathrm{C}\mathrm{H}}_2$: monomer, X: polymer D reaction R: substitution, ${\mathrm{C}\mathrm{H}}_2={\mathrm{C}\mathrm{H}}_2$: polymer, X: monomer

Part of the structure of a polymer is shown. Which statements about the polymer are correct? 1 The polymer is nylon. 2 The polymer is formed by condensation polymerisation. 3 There are ester linkages between the monomers. A 1 and 2 B 2 and 3 C 2 only D 3 only

The concentration of acids and alkalis can be determined by titration. Which pieces of equipment are needed to perform a titration? 1 thermometer 2 pipette 3 gas syringe 4 burette A 1 and 2 B 1 and 3 C 2 and 3 D 2 and 4

Which chromatogram shows how the $R_{\mathrm{f}}$ value of a substance is calculated? A $R_{\mathrm{f}}=\frac{y}{x}$ B $R_{\mathrm{f}}=\frac{y}{x}$ C $R_{\mathrm{f}}=\frac{x}{y}$ D $R_{\mathrm{f}}=\frac{x}{y}$