IGCSE chemistry October/November 2023 multiple choice

A sample of a gas occupies 340 cm³ at room temperature and pressure. The temperature and pressure are both increased, but the volume occupied by the gas remains 340 cm³. Which row describes what happens to the particle speed and the average distance between the particles in the gas when the temperature and pressure are both increased?

• unchanged, unchanged

• unchanged, increased

• increased, unchanged

• increased, increased

Answer explanation

When temperature increases, particle speed increases due to higher energy. Since the volume remains constant, the average distance between particles stays unchanged. Thus, the correct choice is 'increased, unchanged'.

Which statements about the rate of diffusion of the gases ammonia, carbon monoxide, nitrogen, and oxygen are correct?

1. Nitrogen and carbon monoxide will diffuse at the same rate.

2. Oxygen will diffuse slowest because it is an element, whereas the others are compounds.

3. Ammonia will diffuse fastest.

• 1 and 2

• 1 and 3

• 1 only

• 2 and 3

Answer explanation

Statement 1 is correct as nitrogen and carbon monoxide have similar molar masses, leading to similar diffusion rates. Statement 3 is also correct; ammonia, being lighter, diffuses faster than the others. Statement 2 is incorrect.

The structure of an atom of element X is shown. What is element X?

• boron

• carbon

• sodium

• sulfur

Answer explanation

Element X has 5 protons, which corresponds to boron on the periodic table. Carbon has 6 protons, sodium has 11, and sulfur has 16, making boron the only correct choice based on the atomic structure provided.

Which statement explains why isotopes of an element have the same chemical reactions?

• They have different numbers of neutrons.

• They have ions with different numbers of electrons.

• They have the same number of outer shell electrons.

• They have the same number of protons.

Answer explanation

Isotopes of an element have the same number of outer shell electrons, which determines their chemical behavior. This is why they exhibit the same chemical reactions, despite differing numbers of neutrons.

Magnesium reacts with oxygen to form magnesium oxide. What happens to magnesium atoms and oxygen atoms during this reaction?

• Magnesium and oxygen share two electrons.

• Magnesium gains two electrons and oxygen loses two electrons.

• Magnesium loses one electron and oxygen gains one electron.

• Magnesium loses two electrons and oxygen gains two electrons.

Answer explanation

During the reaction, magnesium loses two electrons, becoming a positively charged ion, while oxygen gains those two electrons, becoming a negatively charged ion. This transfer of electrons forms magnesium oxide.

Which row about the properties of both diamond and silicon(IV) oxide is correct?

• Yes, giant covalent

• Yes, simple covalent

• No, giant covalent

• No, simple covalent

Answer explanation

Diamond and silicon(IV) oxide both have a giant covalent structure, meaning they consist of a large network of atoms bonded covalently. Therefore, the correct choice is 'No, giant covalent'.

The equation represents the reaction between solid magnesium oxide and dilute hydrochloric acid to form magnesium chloride and water. Which row shows the state symbols for hydrochloric acid, magnesium chloride and water?

• (aq), (aq), (l)

• (aq), (l), (l)

• (l), (aq), (aq)

• (l), (l), (aq)

Answer explanation

The correct state symbols are (aq) for hydrochloric acid and magnesium chloride, indicating they are in aqueous solution, and (l) for water, which is a liquid. Thus, the answer is (aq), (aq), (l).

Which substance is a mixture?

• air

• graphite

• oxygen

• water

Answer explanation

Air is a mixture of gases, primarily nitrogen and oxygen, along with other trace gases. In contrast, graphite, oxygen, and water are pure substances, making air the correct choice as a mixture.

The number of moles of atoms X, Y and Z, in a compound, are shown. What is the formula of the compound?

• XYZ₄

• XY₄Z₂

• X₂YZ₄

• X₂Y₄Z

Answer explanation

The correct formula is X₂Y₄Z, as it indicates 2 moles of X, 4 moles of Y, and 1 mole of Z, matching the given quantities. Other options do not accurately represent these ratios.

1.0 mol of silver nitrate, AgNO₃, contains 1.2 × 10²⁴ ions. How many ions are there in 0.25 mol of iron(III) oxide, Fe₂O₃?

• 1.5 × 10²³

• 3.0 × 10²³

• 7.5 × 10²³

• 3.0 × 10²⁴