IB Chemistry HL 4.2 Acids and Bases Question Bank

Practise IB Chemistry HL 4.2 with evidence-led questions on acids, bases, pH, neutralization and quantitative analysis.

[Maximum number: 6]

Organic compounds have many industrial applications.

(a)

Ethene reacts with steam to produce ethanol.

\mathrm{C}_{2} \mathrm{H}_{4}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) \rightarrow \mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(\mathrm{~g})

[ 6 ]

(i)

Calculate the enthalpy, in kJ , of the reaction using section 12 of the data booklet.

[ 3 ]

ALTERNATIVE 1:

Bonds broken:

$1 \mathrm{C}=\mathrm{C}+4 \mathrm{C}-\mathrm{H}+2 \mathrm{O}-\mathrm{H} / 614+4(414)+2(463) / 3196$ «kJ»

Bonds formed:

1 C-C+1 C-O+5 C-H+1 O-H /

346+358+5(414)+463 /

3237 «kJ»
$\Delta H=\text { «3196-3237 }=\text { » }-41 \text { «kJ» » }$

ALTERNATIVE 2:

Bonds broken:
$1 \mathrm{C}=\mathrm{C}+1 \mathrm{O}-\mathrm{H} / 614+463 /$

1077 «kJ»

Bonds formed:
$\begin{aligned} & 1 \mathrm{C}-\mathrm{C}+1 \mathrm{C}-\mathrm{O}+1 \mathrm{C}-\mathrm{H} / 346+358+414 / & 1118\langle\mathrm{~kJ}\rangle{ }^{2} & \Delta H=\langle 1077-1118=\rangle-41\left\langle\mathrm{~kJ} \|{ }^{2} \right. \end{aligned}$

Award [3] for correct final answer.

Award [2 max] for +41 «kJ».

(ii)

Calculate the enthalpy of the reaction, in kJ . Use section 13 of the data booklet and $\Delta H_{f}^{\ominus}$ of $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}(\mathrm{g})=-235 \mathrm{~kJ} \mathrm{~mol}^{-1}$ .

[ 2 ]

$\begin{aligned} \text { 《 } \Delta H^{\ominus}=\Sigma\left(\Delta H_{\mathrm{f}}^{\ominus} \text { products }\right)-\Sigma\left(\Delta H_{\mathrm{f}}^{\ominus} \text { reactants }\right) =-235-(+52+(-242)) =-45 \text { «kJ» } \end{aligned}$

Award [2] for correct final answer.

Award [1 max] for +45 «kJ»

(iii)

Outline why the enthalpies calculated in (i) and (ii) are different.

[ 1 ]

[Maximum number: 5]

Solid ionic compounds form crystal lattices.

(a)

Entalpy of solution, enthalpy of hydration and lattice enthalpy are related in an energy cycle.

[ 3 ]

(i)

Annotate the energy cycle for the enthalpy of solution of solid magnesium chloride, $\mathrm{MgCl}_{2}$ (s), by naming the processes A, B and C and completing the boxes. Include state symbols.

Figure for Question (i) — IB Chemistry HL

A:
B:
C:

[ 2 ]

Figure for Answer to Question (i) — IB Chemistry HL

Official Born-Haber/enthalpy cycle labels shown in the figure.

Correct boxes:
- A: enthalpy of solution / $\Delta H$ solution / $\Delta H_{\text{sol}}$ .
- B: lattice enthalpy / $\Delta H_{\text{lattice}}$ .
- C: enthalpy of hydration / $\Delta H_{\text{hydration}}$ .

(ii)

Calculate the enthalpy of solution for magnesium chloride, $\mathrm{MgCl}_{2}$ . Use sections 18 and 20 of the data booklet.

[ 1 ]

$\Delta H_{\text{solution}}=\Delta H_{\text{lattice}}+\Delta H_{\text{hydration}}$ $\Delta H_{\text{solution}}=2540+(-1963)+2(-359) =-141\ \mathrm{kJ\ mol^{-1}}$

(b)

Explain why the lattice enthalpy of barium chloride, $\mathrm{BaCl}_{2}$ , is lower than that of magnesium chloride.

[ 2 ]

ionic radius $\mathrm{Ba}^{2+}$ is greater than that of $\mathrm{Mg}^{2+}$ weaker attraction between « $\mathrm{Ba}^{2+}$ and $\mathrm{Cl}^{-}$ » ions

[Maximum number: 2]

Phosphoryl chloride, $\mathrm{POCl}_{3}$ , is a dehydrating agent.

(a)

$\quad \mathrm{POCl}_{3}(\mathrm{~g})$ decomposes according to the following equation.

2 \mathrm{POCl}_{3}(\mathrm{~g}) \rightarrow 2 \mathrm{PCl}_{3}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g})

[ 2 ]

(i)

Define the term standard enthalpy change of formation, $\Delta H_{\mathrm{f}}{ }^{\ominus}$ .

[ 1 ]

heat/enthalpy change/required/absorbed when 1 mol of a compound is formed from its elements in their standard states/at $100 \mathrm{kPa} / 10^{5} \mathrm{~Pa} / \mathrm{l} \mathrm{bar}$ ; Allow $1.01 \times 10^{5} \mathrm{~Pa} / 101 \mathrm{kPa} / 1 \mathrm{~atm}$ .

Marking guidance:

Allow under standard conditions or standard temperature and pressure.
Temperatures not required in definition, allow if quoted (for example, $298 \mathrm{~K} / 25^{\circ} \mathrm{C}$ - most common) but pressure value must be correct if stated.

(ii)

Calculate the standard enthalpy change for the reaction, $\Delta H^{\ominus}$ , in $\mathrm{kJ} \mathrm{mol}^{-1}$ , using the data below.

Table for Question (ii) — IB Chemistry HL

[ 1 ]

$\left.\left(\Delta H^{\ominus}=[(2)(-288.1)]-[(2)(-542.2)]\right)=\right)(+) 508.2\left(\mathrm{~kJ} \mathrm{~mol}^{-1}\right)$ ;

All question bank results loaded

Covered syllabus points

1.2 Energy cycles question 1

Question (a)

Question (i)

Question (ii)

Question (iii)

1.2 Energy cycles question 2

Question (a)

Question (i)

Question (ii)

Question (b)

1.2 Energy cycles question 3

Question (a)

Question (i)

Question (ii)