Chemistry 9701 · AS & A Level · Nitrogen and sulfur

Nitrogen and sulfur — practice question

Sulfides are compounds that contain sulfur, but they do not contain oxygen.
(a(i))[1]

Carbon disulfide, $\text{CS}_2$, is a volatile liquid at room temperature and pressure. State the meaning of volatile.

(a(ii))[2]

Draw a ‘dot-and-cross’ diagram for the $\text{CS}_2$ molecule.

(a(iii))[1]

Suggest the bond angle in a molecule of $\text{CS}_2$.

(a(iv))[2]

$\text{CS}_2$ is a liquid under room conditions, while $\text{CO}_2$ is a gas. Explain what causes the difference in the physical properties between $\text{CS}_2$ and $\text{CO}_2$.

(b(i))[2]

The enthalpy change of combustion of $\text{CS}_2(l)$ is represented by the following equation: $\text{CS}_2(l) + 3\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{SO}_2(g)$. Define enthalpy change of combustion.

(b(ii))[2]

The table gives the enthalpy changes of formation of $\text{CS}_2(l)$, $\text{CO}_2(g)$ and $\text{SO}_2(g)$. Use the values in the table to calculate the enthalpy change of combustion, $\Delta H_c$, of $\text{CS}_2(l)$, in $\text{kJ mol}^{-1}$. Show your working.

(c(i))[1]

Hydrogen sulfide gas, $\text{H}_2\text{S}(g)$, is slightly soluble in water. It acts as a weak acid in aqueous solution. State the meaning of weak acid.

(c(ii))[1]

Give the formula of the conjugate base of $\text{H}_2\text{S}$.

(c(iii))[2]

$\text{H}_2\text{S}(aq)$ reacts slowly with oxygen dissolved in water. The reaction is represented by the following equation: $\text{H}_2\text{S}(aq) + \tfrac{1}{2}\text{O}_2(aq) \rightarrow \text{H}_2\text{O}(l) + \text{S}(s)$. Explain, with reference to oxidation numbers, why this reaction is a redox reaction.

(d(i))[4]

The compound $\mathrm{As_2S_3}$ is a common mineral. When $\mathrm{As_2S_3}$ is heated strongly in air, it forms a mixture of products, as shown. $\mathrm{2As_2S_3(s)} + \mathrm{9O_2(g)} \rightarrow \mathrm{As_4O_6(s)} + \mathrm{6SO_2(g)}$ A sample containing $0.198\,\mathrm{g}$ $\mathrm{As_2S_3}$ is placed in $0.100\,\mathrm{dm^3}$ of pure oxygen, an excess, in a reaction chamber connected to a gas syringe at room temperature. The reactants are heated until no further change is observed. The products are then allowed to cool to room temperature. Calculate the volume, in $\mathrm{dm^3}$, of gas present at the end of the experiment. The molar volume of gas is $24.0\,\mathrm{dm^3\,mol^{-1}}$ under these conditions. Assume that the pressure is constant throughout the experiment. Show your working.

(d(ii))[1]

State the environmental consequences of releasing $\mathrm{SO_2(g)}$ into the atmosphere.

(d(iii))[2]

$\mathrm{SO_2(g)}$ can be removed from the air by reacting it with $\mathrm{NaOH(aq)}$. Construct an equation for the reaction of $\mathrm{SO_2(g)}$ with $\mathrm{NaOH(aq)}$. Include state symbols.

Worked solution & mark scheme

This 21-mark question has a full step-by-step worked solution and mark scheme. One marking point: Easily evaporates / vaporises readily / changes to gas easily

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