IB Chemistry HL 2.1 Amount of Chemical Change Question Bank

Practise IB Chemistry HL 2.1 with SL and HL questions on balanced equations, mole calculations, limiting reactants, yield and atom economy.

[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.

(c) (i)

Figure for Answer to Question 2.1 Amount of chemical change 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: 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.

[Maximum number: 3]

Phosphine (IUPAC name phosphane) is a hydride of phosphorus, with the formula $\mathrm{PH}_{3}$ .

(a)

2.478 g of white phosphorus was used to make phosphine according to the equation:

\mathrm{P}_{4}(\mathrm{~s})+3 \mathrm{OH}^{-}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow \mathrm{PH}_{3}(\mathrm{~g})+3 \mathrm{H}_{2} \mathrm{PO}_{2}^{-}(\mathrm{aq})

[ 2 ]

(i)

This phosphorus was reacted with $100.0 \mathrm{~cm}^{3}$ of $5.00 \mathrm{~mol} \mathrm{dm}^{-3}$ aqueous sodium hydroxide. Deduce, showing your working, which was the limiting reagent.

[ 1 ]

(ii)

Determine the excess amount, in mol , of the other reagent.

[ 1 ]

amount in excess $\boldsymbol{<}=0.500-(3 \times 0.02000) \underset{0}{0}=0.440$ «mol»

(b)

Impurities cause phosphine to ignite spontaneously in air to form an oxide of phosphorus and water.

[ 1 ]

(i)

State the equation for the reaction of this oxide of phosphorus with water.

[ 1 ]

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Covered syllabus points

2.1 Amount of chemical change question 1

2.1 Amount of chemical change question 2

Question (a)

Question (i)

Question (ii)

Question (b)

Question (i)

Question (c)

Question (i)

2.1 Amount of chemical change question 3

Question (a)

Question (i)

Question (ii)

Question (b)

Question (i)