A Level Chemistry 9701 Paper 21, May/June 2024

The elements of Group 17 are called halogens. Complete Table 1.1. Table 1.1

State the trend in volatility of the halogens chlorine, bromine and iodine. Explain your answer.

Iodine is made by reacting bromine with sodium iodide. Construct an ionic equation for the reaction of bromine with sodium iodide.

State the role of bromine in the reaction. Explain your answer.

Concentrated sulfuric acid is added to separate samples containing equal amounts of $\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}$, $\mathrm{N}\mathrm{a}\mathrm{B}\mathrm{r}$ and $\mathrm{N}\mathrm{a}\mathrm{I}$. All three samples initially react to produce the hydrogen halide. Write an equation to describe the acid–base reaction that occurs when concentrated sulfuric acid reacts with $\mathrm{N}\mathrm{a}\mathrm{B}\mathrm{r}$.

Deduce which sodium halide, $\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}$, $\mathrm{N}\mathrm{a}\mathrm{B}\mathrm{r}$ or $\mathrm{N}\mathrm{a}\mathrm{I}$, produces the largest percentage yield of hydrogen halide when concentrated sulfuric acid is added. Explain your answer by considering the relative reactivity of the halide ions as reducing agents. identity of sodium halide .................................................................................................... explanation ........................................................................................................................

Sulfur chloride, ${\mathrm{S}\mathrm{C}\mathrm{l}}_2$, is a liquid at room temperature. When ${\mathrm{S}\mathrm{C}\mathrm{l}}_2$ is added to water, misty fumes are seen and a solution is made that turns universal indicator red. Identify the type of reaction that occurs when ${\mathrm{S}\mathrm{C}\mathrm{l}}_2$ is added to water.

Name a chloride of a different Period 3 element that is also a liquid at room temperature and produces misty fumes when added to water.

A molecule of ${\mathrm{S}\mathrm{C}\mathrm{l}}_2$ contains two $\mathrm{S}-\mathrm{C}\mathrm{l}$ covalent bonds. Complete the dot-and-cross diagram in Fig. 2.1 to show the arrangement of the outer electrons in a molecule of ${\mathrm{S}\mathrm{C}\mathrm{l}}_2$. Use $\times$ to show electrons from the chlorine atoms. Use $\bullet$ to show electrons from the sulfur atom.

Predict the shape of, and bond angle in, a molecule of ${\mathrm{S}\mathrm{C}\mathrm{l}}_2$ by using VSEPR theory. shape ................................................................................................................................ bond angle ........................................................................................................................

Solid magnesium nitride, ${\mathrm{M}\mathrm{g}}_3{\mathrm{N}}_2$, is a crystalline solid. Deduce the oxidation numbers of magnesium and nitrogen in magnesium nitride to complete Table 2.1. Table 2.1

Magnesium nitride reacts with an excess of water to produce ammonia and magnesium hydroxide only. Construct an equation to describe this reaction.

Explain why the solution produced in the reaction in (c)(ii) has a pH greater than 7. Refer to the products of the reaction in your answer.

Boron nitride is a white solid that melts above $2900{}^{\circ }\mathrm{C}$. Fig. 2.2 shows part of the lattice structure of a crystal of boron nitride. Use Fig. 2.2 to deduce the empirical formula of boron nitride.

Suggest the identity of another crystalline solid that has atoms arranged in layers similar to that of solid boron nitride.

Define Le Chatelier’s principle.

Reaction 1 describes the reversible reaction between yellow ${\mathrm{F}\mathrm{e}}^{3+}(\mathrm{a}\mathrm{q})$ and colourless ${\mathrm{S}\mathrm{C}\mathrm{N}}^{-}(\mathrm{a}\mathrm{q})$ to produce red ${\mathrm{F}\mathrm{e}\mathrm{S}\mathrm{C}\mathrm{N}}^{2+}(\mathrm{a}\mathrm{q})$. $$\text{reaction 1}{\mathrm{F}\mathrm{e}}^{3+}(\mathrm{a}\mathrm{q})+{\mathrm{S}\mathrm{C}\mathrm{N}}^{-}(\mathrm{a}\mathrm{q})\rightleftharpoons {\mathrm{F}\mathrm{e}\mathrm{S}\mathrm{C}\mathrm{N}}^{2+}(\mathrm{a}\mathrm{q})\mathrm{\Delta }H=-x\text{ kJ}{\text{mol}}^{-1}$$ $$\text{yellow}\text{colourless}\text{red}$$ A mixture of ${\mathrm{F}\mathrm{e}}^{3+}(\mathrm{a}\mathrm{q})$, ${\mathrm{S}\mathrm{C}\mathrm{N}}^{-}(\mathrm{a}\mathrm{q})$ and ${\mathrm{F}\mathrm{e}\mathrm{S}\mathrm{C}\mathrm{N}}^{2+}(\mathrm{a}\mathrm{q})$ is at equilibrium at $20{}^{\circ }\mathrm{C}$. The temperature of this mixture is then increased to $50{}^{\circ }\mathrm{C}$ and allowed to reach equilibrium. Deduce the changes that occur, if any, in the equilibrium mixture at $50{}^{\circ }\mathrm{C}$ compared to the equilibrium mixture at $20{}^{\circ }\mathrm{C}$. • change in appearance • change in relative concentration of ${\mathrm{F}\mathrm{e}\mathrm{S}\mathrm{C}\mathrm{N}}^{2+}(\mathrm{a}\mathrm{q})$ • change in value of the equilibrium constant, $K_c$

In another experiment, equimolar amounts of ${\mathrm{F}\mathrm{e}}^{3+}(\mathrm{a}\mathrm{q})$ and ${\mathrm{S}\mathrm{C}\mathrm{N}}^{-}(\mathrm{a}\mathrm{q})$ are mixed together and allowed to reach equilibrium. The total volume of the mixture is $25.0{\text{ cm}}^3$. $$\text{reaction 1}{\mathrm{F}\mathrm{e}}^{3+}(\mathrm{a}\mathrm{q})+{\mathrm{S}\mathrm{C}\mathrm{N}}^{-}(\mathrm{a}\mathrm{q})\rightleftharpoons {\mathrm{F}\mathrm{e}\mathrm{S}\mathrm{C}\mathrm{N}}^{2+}(\mathrm{a}\mathrm{q})$$ At equilibrium the mixture contains: • $[{\mathrm{S}\mathrm{C}\mathrm{N}}^{-}]=1.30\times {10}^{-3}\text{ mol}{\text{dm}}^{-3}$ • $[{\mathrm{F}\mathrm{e}\mathrm{S}\mathrm{C}\mathrm{N}}^{2+}]=0.300\times {10}^{-3}\text{ mol}{\text{dm}}^{-3}$. Calculate the initial amount, in mol, of ${\mathrm{F}\mathrm{e}}^{3+}(\mathrm{a}\mathrm{q})$ added to ${\mathrm{S}\mathrm{C}\mathrm{N}}^{-}(\mathrm{a}\mathrm{q})$ to produce this mixture. initial amount of ${\mathrm{F}\mathrm{e}}^{3+}(\mathrm{a}\mathrm{q})$ = .............................. mol

Calculate $K_c$ for reaction 1 and state its units. Show your working. $K_c$ = .............................. units ..............................

Define enthalpy change of formation.

Iron is made when iron(III) oxide is heated with carbon monoxide, as shown by reaction 2. $$\text{reaction 2}{\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3+3\mathrm{C}\mathrm{O}\to 2\mathrm{F}\mathrm{e}+3{\mathrm{C}\mathrm{O}}_2$$ Table 4.1 shows enthalpy change of formation data measured at $298\text{ K}$ and $101\text{ kPa}$. Complete Table 4.1 by adding equations with relevant state symbols to represent: • standard enthalpy change of formation for ${\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3$ • standard enthalpy change of formation for $\mathrm{C}\mathrm{O}$.

Use the data in Table 4.1 to calculate the enthalpy change of reaction, $\mathrm{\Delta }{H}_r$, in $\text{kJ}{\text{mol}}^{-1}$, for reaction 2. Show your working. $\mathrm{\Delta }{H}_r$ = .............................. $\text{kJ}{\text{mol}}^{-1}$

Define covalent bond.

A $\mathrm{C}=\mathrm{C}$ bond in an alkene is made from a $\sigma$ bond and a $\pi$ bond. Identify the hybridisation of the carbon atoms in a $\mathrm{C}=\mathrm{C}$ bond in an alkene.

Draw labelled diagrams to show, in terms of orbital overlap, how the $\sigma$ and $\pi$ bonds are made in a $\mathrm{C}=\mathrm{C}$ bond. $\sigma$ bond $\pi$ bond

In electrophilic reactions involving alkenes the $\pi$ bond of $\mathrm{C}=\mathrm{C}$ is broken. Suggest one difference between $\sigma$ and $\pi$ bonds that explains why the $\pi$ bond is broken in electrophilic addition reactions involving alkenes.

Complete Fig. 5.1 to show the mechanism for the electrophilic addition of hydrogen bromide to 2-methylpropene to produce the major organic product. Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate.

$\mathbf{V}$ shows stereoisomerism. Explain what is meant by stereoisomerism.

Deduce the number of stereoisomers of $\mathbf{V}$. Explain your reasoning.

Deduce the molecular formula of $\mathbf{V}$.

Name all the functional groups present in $\mathbf{V}$.

Fig. 6.2 shows two reactions involving $\mathbf{V}$. Identify the role of reagent $\mathbf{T}$ for each functional group that reacts in reaction 1.

Suggest the identity of reagent $\mathbf{U}$ in reaction 2.

Both functional groups in one molecule of $\mathbf{Y}$ react with an inorganic reagent to form one molecule of $\mathbf{Q}$ and one molecule of methanol, ${\mathrm{C}\mathrm{H}}_3\mathrm{O}\mathrm{H}$, as shown in Fig. 6.3. Part of the mass spectrum for $\mathbf{Q}$ is shown in Fig. 6.4. Only peaks with $m\mathrm{/}e$ greater than 198 are shown. Calculate the relative abundance, $x$, of the peak at $m\mathrm{/}e=201$. Show your working. x = ..............................

$\mathbf{Q}$ contains only hydroxyl functional groups. Complete Table 6.1 to show the observations that occur when 2,4-dinitrophenylhydrazine (2,4-DNPH reagent) is added to separate samples of $\mathbf{Y}$ and $\mathbf{Q}$. Table 6.1

Under certain conditions, $0.0020\text{ mol}$ of $\mathbf{Q}$ reacts with an excess of sodium to produce a total of $44.8{\text{ cm}}^3$ of gas at s.t.p. Calculate the number of hydroxyl groups present in a molecule of $\mathbf{Q}$. Show your working. number of hydroxyl groups = ..............................

Use Table 6.2 to describe and explain two differences between the infrared spectrum of $\mathbf{Y}$ and $\mathbf{Q}$ in the region above $1500{\text{ cm}}^{-1}$.