Chemistry 9701 · AS & A Level · Nitrogen and sulfur

Nitrogen and sulfur — practice question

Sulfides are compounds containing sulfur and no oxygen.
(a(i))[1]

Carbon disulfide, $\text{CS}_2$, is a volatile liquid at room temperature and pressure. State what is meant by \emph{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, whereas $\text{CO}_2$ is a gas. Explain the reason for the difference in their physical properties.

(b(i))[2]

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

(b(ii))[2]

The table lists the enthalpy changes of formation for $\text{CS}_2(l)$, $\text{CO}_2(g)$ and $\text{SO}_2(g)$. $\Delta H_f(\text{CS}_2(l)) = +89.7\ \text{kJ mol}^{-1}$ $\Delta H_f(\text{CO}_2(g)) = -394\ \text{kJ mol}^{-1}$ $\Delta H_f(\text{SO}_2(g)) = -297\ \text{kJ mol}^{-1}$ Use the data 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 only slightly soluble in water. It behaves as a weak acid in aqueous solution. State what is meant by \emph{weak acid}.

(c(ii))[1]

State 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 equation below. $\text{H}_2\text{S}(aq) + \tfrac{1}{2}\text{O}_2(aq) \rightarrow \text{H}_2\text{O}(l) + \text{S}(s)$ Explain, using oxidation numbers, why this reaction is a redox reaction.

(d(i))[4]

A sample containing $0.198\,\text{g}$ of $\text{As}_2\text{S}_3$ is put into $0.100\,\text{dm}^3$ of pure oxygen, which is in excess, in a reaction chamber connected to a gas syringe at room temperature. The reactants are heated until no further change is seen. The products are then allowed to cool to room temperature. Calculate the volume, in $\text{dm}^3$, of gas present at the end of the experiment. Under these conditions, the molar volume of gas is $24.0\,\text{dm}^3\,\text{mol}^{-1}$. Assume that the pressure stays constant throughout the experiment. Show your working.

(d(ii))[1]

State the environmental effects of releasing $\text{SO}_2(g)$ into the atmosphere.

(d(iii))[2]

$\text{SO}_2(g)$ can be removed from the air by reacting it with $\text{NaOH}(aq)$. Construct an equation for the reaction of $\text{SO}_2(g)$ with $\text{NaOH}(aq)$. 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 evaporated / evaporates readily / changes into a gas easily

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