IB Chemistry HL 1.5 Chemical Quantities Question Bank

Practise IB Chemistry HL 1.5 with evidence-led questions on moles, equations, chemical quantities and quantitative data.

Covered syllabus points

2.1 Amount of chemical change 2.2 Rate of chemical change 2.3 Extent of chemical change

[Maximum number: 1]

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

State the balanced chemical equation for the reaction of $\mathrm{PCl}_{3}(1)$ with water.

Figure for Answer to Question Reactivity 2. How much, how fast and how far? question 1 — IB Chemistry HL

Allow any combination of dots/crosses or lines to represent electron pairs. Do not penalise missing lone pairs on Cl if already penalised in (b)(i).
(ii) trigonal/triangular bipyramidal;

Do not allow ECF from Lewis structures with incorrect number of negative charge centres.
(iii) $120^{\circ}$ and $90^{\circ} / 180^{\circ}$ ;

Ignore other bond angles such as $240^{\circ}$ and $360^{\circ}$ .
Apply list principle if some correct and incorrect angles given.

[Maximum number: 12]

The reaction between hydrogen and nitrogen monoxide is thought to proceed by the mechanism shown below.

\begin{array}{ll} 2 \mathrm{NO}(\mathrm{~g}) \rightleftharpoons \mathrm{N}_{2} \mathrm{O}_{2}(\mathrm{~g}) & \text { fast equilibrium } \\ \mathrm{N}_{2} \mathrm{O}_{2}(\mathrm{~g})+\mathrm{H}_{2}(\mathrm{~g}) \rightarrow \mathrm{N}_{2} \mathrm{O}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) & \text { slow reaction } \\ \mathrm{N}_{2} \mathrm{O}(\mathrm{~g})+\mathrm{H}_{2}(\mathrm{~g}) \rightarrow \mathrm{N}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g}) & \text { fast reaction } \end{array}

(a)

State the equation for the overall reaction.

[ 1 ]

$2 \mathrm{NO}(\mathrm{g})+2 \mathrm{H}_{2}(\mathrm{~g}) \rightarrow \mathrm{N}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{g}) \downarrow$

(b)

Deduce the rate expression consistent with this mechanism.

[ 1 ]

rate $=k[\mathrm{NO}]^{2}\left[\mathrm{H}_{2}\right]$

(c)

Explain how you would attempt to confirm this rate expression, giving the results you would expect.

[ 3 ]

test the effect «on the reaction rate» of varying each concentration «independently»

OR

test the effect of varying [NO] «on rate», whilst keeping $\left[\mathrm{H}_{2}\right]$ constant AND test effect of varying $\left[\mathrm{H}_{2}\right]$ «on rate», whilst keeping [NO] constant

rate proportional to [NO] ${ }^{2}$

OR

doubling [NO] quadruples rate

rate proportional to $\left[\mathrm{H}_{2}\right]$

OR

doubling $\left[\mathrm{H}_{2}\right]$ doubles rate

Remember to refer back to a (ii) for ECF.

If only one species in rate expression, third mark can be awarded for zero order discussion.

(d)

State, giving your reason, whether confirmation of the rate expression would prove that the mechanism given is correct.

[ 1 ]

(e)

Suggest how the rate of this reaction could be measured experimentally.

[ 1 ]

(f)

The enthalpy change for the reaction between nitrogen monoxide and hydrogen is -664 kJ and its activation energy is 63 kJ .

[ 5 ]

(i)

Sketch the potential energy profile for the overall reaction, using the axes given, indicating both the enthalpy of reaction and activation energy.

[ 2 ]

(ii)

This reaction is normally carried out using a catalyst. Draw a dotted line labelled "Catalysed" on the diagram above to indicate the effect of the catalyst.

$(iii) Sketch and label a second Maxwell-Boltzmann energy distribution curve representing the same system but at a higher temperature, \(T_{\text {higher$

(iii) Sketch and label a second Maxwell-Boltzmann energy distribution curve representing the same system but at a higher temperature, \(T_{\text {higher

[ 1 ]

(iii)

Explain why an increase in temperature increases the rate of this reaction.

Figure for Question (iii) — IB Chemistry HL

[ 2 ]

[Maximum number: 9]

Nitrous acid, $\mathrm{HNO}_{2}$ , is a weak acid which can be used to make acidic buffers.

(a)

A catalyst, usually concentrated sulfuric acid, $\mathrm{H}_{2} \mathrm{SO}_{4}$ , is used in the manufacture of this ester.

Explain the action of a catalyst.

[ 2 ]

(b)

The overall reaction for the synthesis of ethyl ethanoate from ethane is:

2 \mathrm{C}_{2} \mathrm{H}_{6}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g})+\frac{3}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}(\mathrm{~g})+2 \mathrm{HCl}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g})

[ 2 ]

(i)

The progress of the reaction was followed until equilibrium was reached.

Sketch a graph showing how the rates of the forward and reverse reactions change from the beginning of the reaction, until equilibrium has been reached.

Figure for Question (i) — IB Chemistry HL

[ 2 ]

(c)

A student attempted to confirm the value for K obtained in (d)(viii).
0.6 moles each of ethanol and ethanoic acid reacted in the presence of an acid catalyst. The volume remained constant. After 10 minutes, 0.2 moles of ethanoic acid remained in the reaction mixture.

K=\frac{\left[\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}\right]\left[\mathrm{H}_{2} \mathrm{O}\right]}{\left[\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\right]\left[\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2}\right]}

Determine the student's experimental value of K under these conditions.

[ 3 ]

«moles of» ethanol «at equilibrium» =0.2 «moles of» ethyl ethanoate «at equilibrium» =0.4 «moles of» water «at equilibrium» =0.4

$\frac{0.4^{2}}{0.2^{2}}$ $\frac{<0.16 \gg}{<0.04>} 4.0$

Marking guidance:

Award [3] for correct final answer.

M1 can be awarded for a correct expression for M2.

(d)

Suggest a reason for the difference between the value of the equilibrium constant, K, determined from experimental values in (e)(i) and the correct value calculated for K, in (d)(viii).

If you did not obtain values for these, use 7.15 for (d)(viii) and 3.75 for (e)(i), although these are not the correct values.

[ 1 ]

(e)

State the correct name for the value determined in e(i).

[ 1 ]

[Maximum number: 6]

Two groups of students (Group A and Group B) carried out a project* on the chemistry of some group 7 elements (the halogens) and their compounds.

(a)

In the first part of the project, the two groups had a sample of iodine monochloride (a corrosive brown liquid) prepared for them by their teacher using the following reaction.

\mathrm{I}_{2}(\mathrm{~s})+\mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{ICl}(\mathrm{l})

The following data were recorded.

Table for Question (a) — IB Chemistry HL

[ 4 ]

(i)

The iodine used in the reaction was in excess. Determine the theoretical yield, in g , of ICl(l).

[ 3 ]

(ii)

Calculate the percentage yield of ICl(l).

[ 1 ]

$\quad\left(\frac{8.60}{10.3} \times 100=\right) 83.5 \%$ ;

Marking guidance:

Allow answers in the range of 82.5 to 84.5\%.

(b)

The students reacted ICl(l) with CsBr(s) to form a yellow solid, $\mathrm{CsICl}_{2}(\mathrm{~s})$ , as one of the products. $\mathrm{CsICl}_{2}(\mathrm{~s})$ has been found to produce very pure CsCl(s) which is used in cancer treatment.

To confirm the composition of the yellow solid, Group A determined the amount of iodine in 0.2015 g of $\mathrm{CsICl}_{2}(\mathrm{~s})$ by titrating it with $0.0500 \mathrm{moldm}^{-3} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}(\mathrm{aq})$ . The following data were recorded for the titration.

Table for Question (b) — IB Chemistry HL

[ 1 ]

(i)

The overall reaction taking place during the titration is:

Calculate the amount, in mol, of iodine atoms, I , present in the sample of $\mathrm{CsICl}_{2}(\mathrm{~s})$ .

[ 1 ]

$\left(0.5 \times 1.21 \times 10^{-3}\right)=6.05 \times 10^{-4} / 0.000605(\mathrm{~mol})$ ;

Marking guidance:

Accept alternate method e.g. $(0.384 / 126.9 \times 0.2015)=6.10 \times 10^{-4} / 0.000610(\mathrm{~mol})$ .

(c)

In this project the students explored several aspects of the chemistry of the halogens. In the original preparation of $\operatorname{ICl}(1)$ , they observed the yellow-green colour of chlorine gas, $\mathrm{Cl}_{2}(\mathrm{~g})$ , reacting with solid iodine, $\mathrm{I}_{2}(\mathrm{~s})$ .

[ 1 ]

(i)

Chlorine can also react with water. State the balanced chemical equation for the reaction of $\mathrm{Cl}_{2}(\mathrm{~g})$ with water.

[ 1 ]

$\mathrm{Cl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightleftharpoons \mathrm{HCl}(\mathrm{aq})+\mathrm{HOCl}(\mathrm{aq})$ ;

Marking guidance:

Accept →.
Accept HClO(aq).
Allow $\mathrm{H}^{+}(\mathrm{aq})+\mathrm{Cl}^{-}(\mathrm{aq})$ for HCl(aq) and $\mathrm{H}^{+}(\mathrm{aq})+{ }^{-} \mathrm{OCl}_{(\mathrm{aq})} / \mathrm{OCl}^{-}(\mathrm{aq}) / \mathrm{ClO}^{-}(\mathrm{aq})$ for HOCl(aq).

Ignore state symbols.

All question bank results loaded

Covered syllabus points

Reactivity 2. How much, how fast and how far? question 1

Reactivity 2. How much, how fast and how far? question 2

Question (a)

Question (b)

Question (c)

Question (d)

Question (e)

Question (f)

Question (i)

Question (ii)

Question (iii)

Reactivity 2. How much, how fast and how far? question 3

Question (a)

Question (b)

Question (i)

Question (c)

Question (d)

Question (e)

Reactivity 2. How much, how fast and how far? question 4

Question (a)

Question (i)

Question (ii)

Question (b)

Question (i)

Question (c)

Question (i)