The diagrams show part of the structures of five substances, $\mathbf{A}, \mathbf{B}, \mathbf{C}, \mathbf{D}$ and $\mathbf{E}$.
(a) Answer the following questions about these structures.
Each structure may be used once, more than once or not at all.
l.
(i) Which two of these structures, $\mathbf{A}, \mathbf{B}, \mathbf{C}, \mathbf{D}$ or $\mathbf{E}$, are covalently bonded? [2]
(ii) Which one of these structures, $\mathbf{A}, \mathbf{B}, \mathbf{C}, \mathbf{D}$ or $\mathbf{E}$, is a diatomic molecule? [1]
(iii) Which one of these structures, $\mathbf{A}, \mathbf{B}, \mathbf{C}, \mathbf{D}$ or $\mathbf{E}$, is a compound? [1]
(iv) Which one of these structures, $\mathbf{A}, \mathbf{B}, \mathbf{C}, \mathbf{D}$ or $\mathbf{E}$, is very soluble in water? [1]
(v) Which one of these structures, $\mathbf{A}, \mathbf{B}, \mathbf{C}, \mathbf{D}$ or $\mathbf{E}$, is used in cutting tools? [1]
(vi) Which one of these structures, $\mathbf{A}, \mathbf{B}, \mathbf{C}, \mathbf{D}$ or $\mathbf{E}$, is used in electrical wiring? [1]
(b) Substance $\mathbf{B}$ is an element.
What is meant by the term element? [1] [Total: 8]
▶️ Answer/Explanation
(a)(i) Ans: B and D
B (diamond) has a giant covalent structure with carbon atoms bonded covalently. D (N₂) has a simple covalent molecule with nitrogen atoms sharing electrons.
(a)(ii) Ans: D
D (N₂) is a diatomic molecule as it consists of two nitrogen atoms bonded together.
(a)(iii) Ans: C
C (LiCl) is a compound formed by lithium and chlorine atoms in a fixed ratio, showing ionic bonding.
(a)(iv) Ans: C
C (LiCl) is very soluble in water due to its ionic nature, which allows it to dissociate into Li⁺ and Cl⁻ ions.
(a)(v) Ans: B
B (diamond) is used in cutting tools because of its extreme hardness resulting from the strong covalent bonds.
(a)(vi) Ans: E
E (copper) is used in electrical wiring due to its high electrical conductivity as a metal.
(b) Ans: An element is a substance in which all the atoms have the same proton number or a substance containing only one type of atom.
(a) A list of formulae is shown.
$\begin{aligned} & \mathrm{AlCl}_3 \\ & \mathrm{CaCO}_3 \\ & \mathrm{CO} \\ & \mathrm{CO}_2 \\ & \mathrm{CoCl}_2 \\ & \mathrm{CuSO}_4 \\ & \mathrm{MgCl}_2 \\ & \mathrm{~N}_2 \\ & \mathrm{NaCl}_2 \\ & \mathrm{NH}_3 \\ & \mathrm{O}_2 \\ & \mathrm{SO}_2\end{aligned}$
Answer the following questions using these formulae.
Each formula may be used once, more than once or not at all.
State which formula represents:
(i) a compound that changes colour from white to blue when water is added
(ii) a compound that is used to make cement
(iii) an element that forms 78% of clean, dry air
(iv) a compound that contains an ion with a single positive charge
(v) a compound that dissolves in water to form an alkaline solution.
(b) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of ammonia.
(c) State whether magnesium oxide is a basic oxide or an acidic oxide. Give a reason for your answer.
▶️ Answer/Explanation
(a)
(i) Ans: \(\mathrm{CuSO_4}\)
Copper(II) sulfate is white when anhydrous and turns blue upon hydration.
(ii) Ans: \(\mathrm{CaCO_3}\)
Calcium carbonate is a key ingredient in cement production.
(iii) Ans: \(\mathrm{N_2}\)
Nitrogen gas constitutes 78% of Earth’s atmosphere.
(iv) Ans: \(\mathrm{NaCl}\)
Sodium chloride contains Na\(^+\) ions with a single positive charge.
(v) Ans: \(\mathrm{NH_3}\)
Ammonia dissolves in water to form ammonium hydroxide, an alkaline solution.
(b)
The dot-and-cross diagram should show:
– 3 bonding pairs (shared electrons) between N and each H (1)
– 1 lone pair (non-bonding electrons) on the N atom (1).
(c) Ans: Basic oxide
Magnesium oxide is basic because it reacts with acids to form salts and water, a characteristic of metal oxides.