AS & A Level Chemistry - 9701 Paper 2 2016 Winter Zone 2

A 0.50 g sample of a Group 2 metal, M, was added to 40.0 cm³ of 1.00 mol dm⁻³ hydrochloric acid (an excess).
equation 1 M(s) + 2HCl(aq) → MCl₂(aq) + H₂(g)

(a) Calculate the amount, in moles, of hydrochloric acid present in 40.0 cm³ of 1.00 mol dm⁻³ HCl.

amount = .................................................. mol [1]

(b) When the reaction had finished, the resulting solution was made up to 100 cm³ in a volumetric flask.

A 10.0 cm³ sample of the solution from the volumetric flask required 15.0 cm³ of 0.050 mol dm⁻³ sodium carbonate solution, Na₂CO₃, for complete neutralisation of the remaining hydrochloric acid.

(i) Write the equation for the complete reaction of sodium carbonate with hydrochloric acid.
....................................................................................................................... ........... [1]

(ii) Calculate the amount, in moles, of sodium carbonate needed to react with the hydrochloric acid in the 10.0 cm³ sample from the volumetric flask.

amount = .................................................. mol [1]

(iii) Calculate the amount, in moles, of hydrochloric acid in the 10.0 cm³ sample.

amount = .................................................. mol [1]

(iv) Calculate the total amount, in moles, of hydrochloric acid remaining after the reaction shown in equation 1.

amount = .................................................. mol [1]

(v) Use your answers to (a) and (b)(iv) to calculate the amount, in moles, of hydrochloric acid that reacted with the 0.50 g sample of M.

amount = .................................................. mol [1]

(vi) Use your answer to (v) and equation 1 to calculate the amount, in moles, of M in the 0.50 g sample.

amount = .................................................. mol [1]

(vii) Calculate the relative atomic mass, $A_r$, of M and identify M.

$A_r$ of M = .........................................
identity of M = ......................................... [2]

Dinitrogen tetroxide, $N_2O_4$, and nitrogen dioxide, $NO_2$, exist in dynamic equilibrium with each other.

$N_2O_4(g) \rightleftharpoons 2NO_2(g)$ $\Delta H = +54 \text{ kJ mol}^{-1}$

The energy profile for this reaction is shown.

[Image_1: Energy profile diagram]

(a) Add labelled arrows to the energy profile to indicate

• the enthalpy change of the reaction, $\Delta H$,
• the activation energy of the forward reaction, $E_a$.

[2]

(b) 0.0500 mol of $N_2O_4$ was placed in a sealed vessel of volume 1.00 dm³, at a temperature of 50°C and a pressure of $1.68 \times 10^5$ Pa. The mass of the resulting equilibrium mixture was 4.606 g.

(i) Calculate the average molecular mass, $M_r$, of the resulting equilibrium mixture. Give your answer to three significant figures.
$M_r = \text{...............................}$ [2]

(ii) The number of moles of $N_2O_4$ that dissociated can be represented by $n$.
State, in terms of $n$, the amount, in moles, of $NO_2$ in the equilibrium mixture.
moles of $NO_2$ = \text{...............................} [1]

The number of moles of $N_2O_4$ remaining at equilibrium is $(0.05 - n)$.
(iii) State, in terms of $n$, the total amount, in moles, of gas in the equilibrium mixture.
[1]

(iv) State, in terms of $n$, the mole fraction of $NO_2$ in the equilibrium mixture.
[1]

In this equilibrium mixture, the mole fraction of $NO_2$ is 0.400.
(v) Use your answers to (ii) and (iv) to calculate the amount in moles of each gas in the equilibrium mixture. Give your answers to three significant figures.

amount of $N_2O_4$ = \text{............................... mol}
amount of $NO_2$ = \text{............................... mol} [2]

(vi) Write the expression for the equilibrium constant, $K_p$, for this equilibrium.
$K_p = \text{...............................}$ [1]

(vii) Use the total pressure of the mixture, $1.68 \times 10^5$ Pa, to calculate the value of the equilibrium constant, $K_p$, and give its units.

$K_p = \text{...............................}$
units = \text{...............................} [3]

The Periodic Table is arranged such that the properties of the elements show a number of trends.
(a) A plot of the first ionisation energies for the first 18 elements is shown.

(i) Explain why the values show a general increase from atomic number 11 to 18.
...............................................................................................................................................................................................
...............................................................................................................................................................................................
............................................................................................................................................................................................... [2]
(ii) Explain the decreases in first ionisation energies between
• atomic numbers 12 and 13,
...............................................................................................................................................................................................
...............................................................................................................................................................................................
...............................................................................................................................................................................................
• atomic numbers 15 and 16.
...............................................................................................................................................................................................
...............................................................................................................................................................................................
............................................................................................................................................................................................... [4]
(iii) Suggest an explanation for the trend in the first ionisation energies of the elements with atomic numbers 2, 10 and 18.
...............................................................................................................................................................................................
...............................................................................................................................................................................................
............................................................................................................................................................................................... [2]

(b) A plot of the melting points of the elements across the third period is shown.

(i) Explain the increase in melting point from atomic number 11 to 12.
...............................................................................................................................................................................................
...............................................................................................................................................................................................
............................................................................................................................................................................................... [2]
(ii) Suggest a reason why the increase from atomic number 12 to 13 is much smaller than the increase from atomic number 11 to 12.
...............................................................................................................................................................................................
............................................................................................................................................................................................... [1]
(iii) State and explain the pattern of the melting points from atomic number 15 to 18.
...............................................................................................................................................................................................
...............................................................................................................................................................................................
...............................................................................................................................................................................................
............................................................................................................................................................................................... [3]
(iv) Explain why the element with atomic number 14 has a melting point so much higher than the rest of the elements in the third period.
...............................................................................................................................................................................................
...............................................................................................................................................................................................
............................................................................................................................................................................................... [1]

(a) $\text{CH}_3\text{CH}_2\text{CHBrCH}_3$
(i) Name this compound.
.................................................................................................................................[1]

(ii) This compound shows stereoisomerism.
Draw the two stereoisomers in the conventional way.
......................................
......................................
......................................
......................................
[2]

(iii) Give the structures of \textbf{three} other structural isomers of $\text{C}_4\text{H}_9\text{Br}$.

[3]

(b) $(\text{C}_2\text{H}_5)_3\text{CBr}$
(i) Name this compound.
.................................................................................................................................[1]

(ii) $(\text{C}_2\text{H}_5)_3\text{CBr}$ reacts with aqueous $\text{OH}^-$.
Complete the mechanism for this reaction including all necessary curly arrows, charges, partial charges and lone pairs.

[3]

(iii) What \textit{type of mechanism} occurs in (ii)?
.................................................................................................................................[1]

(c) $\text{CH}_3\text{CH}_2\text{CH}_2\text{CHBrCH}_3$
(i) Give the reagents and conditions necessary for the conversion of this compound into a mixture of alkenes.
.................................................................................................................................
.................................................................................................................................[2]

(ii) Give the name of the mechanism for the conversion in (i).
.................................................................................................................................[1]

(iii) Draw the skeletal formulae of the three alkenes produced by the conversion in (i).

[3]

(a) Six particles are listed.
\[ \text{H}\bullet \quad \text{H}^+ \quad \text{Cl}\bullet \quad \text{Cl}^- \quad \cdot \text{CH}_3 \quad \text{CH}_3^+ \]
(i) Identify two particles produced during the reaction of methane and chlorine in the presence of UV light.
............................................................................................................................................ [1]
(ii) Identify the two particles produced by the heterolytic fission of a bond in chloromethane.
............................................................................................................................................ [1]

(b) Seven reaction types are listed.
addition substitution oxidation elimination
hydrolysis condensation reduction
(i) Name the type of reaction involved when Tollens’ reagent is used to identify an aldehyde.
............................................................................................................................................ [1]
(ii) Name the type of reaction involved in the test for a carbonyl group using 2,4-DNPH.
............................................................................................................................................ [1]
(iii) Name the type of reaction involved in the reaction of a ketone with NaBH₄.
............................................................................................................................................ [1]
(iv) Name the type of reaction involved in the reaction of an aldehyde with HCN.
............................................................................................................................................ [1]