IB Chemistry SL 1.4 The Mole Questions

Practise IB Chemistry SL 1.4 The Mole by converting amounts into masses and particles, deriving formulae from composition data and solving solution and gas calculations.

Exam points

Convert between mass, amount and specified particle counts using n=m/M and Avogadro’s constant.
Calculate molar mass in g mol⁻¹ from a formula, including hydrated salts.
Define Aᵣ against carbon-12, then calculate Mᵣ or percentage composition from a formula.
Derive empirical formulae from composition data and molecular formulae using Mᵣ.
Calculate c=n/V with correct cm³–dm³ conversion, then solve dilution and mixing problems.
Use balanced-equation mole ratios and titration data to find unknown amounts or concentrations.
Apply Avogadro’s law and balanced gas ratios to calculate volumes at stated conditions.

Covered syllabus points

1.4.1—Mole (mol)1.4.2—Relative atomic mass (Ar) and relative formula mass (Mr)1.4.3—Molar mass (M)1.4.4—Empirical and molecular formulas 1.4.5—Molar concentration 1.4.6—Avogadro's law

[Maximum number: 1]

How many ions are present in 0.20 mol of $\left(\mathrm{NH}_{4}\right)_{2} \mathrm{SO}_{4}$ ?

$0.20 \times 1 \times 6 \times 10^{23}$

$0.20 \times 2 \times 6 \times 10^{23}$

$0.20 \times 3 \times 6 \times 10^{23}$

$0.20 \times 7 \times 6 \times 10^{23}$

[Maximum number: 1]

The element boron has two naturally occurring isotopes, ${ }^{10} \mathrm{~B}$ and ${ }^{11} \mathrm{~B}$ .

The percentage abundance of the isotopes of boron can be determined with a mass spectrometer. The diagram shows the operation of a mass spectrometer.

Identify the species that is used as the scale for the mass of the isotopes.

[Maximum number: 3]

Chlorine undergoes many reactions.

(a)

2.67 g of manganese(IV) oxide was added to $200.0 \mathrm{~cm}^{3}$ of $2.00 \mathrm{moldm} \mathrm{m}^{-3} \mathrm{HCl}$ .

\mathrm{MnO}_{2}(\mathrm{~s})+4 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{Cl}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{MnCl}_{2}(\mathrm{aq})

[ 1 ]

(i)

Calculate the amount, in mol, of manganese(IV) oxide added.

[ 1 ]

n(\mathrm{MnO_2})=\frac{2.67\,\mathrm{g}}{86.94\,\mathrm{g\,mol^{-1}}}=0.0307\,\mathrm{mol}

(b)

$\mathrm{CCl}_{2} \mathrm{~F}_{2}$ is a common chlorofluorocarbon, CFC.

[ 2 ]

(i)

Calculate the percentage by mass of chlorine in $\mathrm{CCl}_{2} \mathrm{~F}_{2}$ .

[ 2 ]

$M(\mathrm{CCl_2F_2})=120.91\ \mathrm{g\ mol^{-1}}$ $\frac{2\times35.45}{120.91}\times100=58.64\%$

Award [2] for correct final answer.

[Maximum number: 1]

Chlorine undergoes many reactions.

2.67 g of manganese(IV) oxide was added to $200.0 \mathrm{~cm}^{3}$ of $2.00 \mathrm{moldm} \mathrm{m}^{-3} \mathrm{HCl}$ .

\mathrm{MnO}_{2}(\mathrm{~s})+4 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{Cl}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})+\mathrm{MnCl}_{2}(\mathrm{aq})

Calculate the amount, in mol, of manganese(IV) oxide added.

n(\mathrm{MnO_2})=\frac{2.67\,\mathrm{g}}{86.94\,\mathrm{g\,mol^{-1}}}=0.0307\,\mathrm{mol}

[Maximum number: 1]

A hydrocarbon has the empirical formula $\mathrm{C}_{3} \mathrm{H}_{7}$ . When 1.17 g of the compound is heated to $85^{\circ} \mathrm{C}$ at a pressure of 101 kPa it occupies a volume of $400 \mathrm{~cm}^{3}$ .

Deduce the molecular formula of the compound.

$\quad \mathrm{C}_{6} \mathrm{H}_{14}$ ;

[Maximum number: 1]

Phenylethene (styrene) is produced from ethylbenzene in a gas-phase equilibrium.

Benzoic acid is a weak acid. The graph shows how the pH changes during the titration of a $10.0 \mathrm{~cm}^{3}$ aqueous solution of benzoic acid with aqueous sodium hydroxide.

Calculate the concentration of the benzoic acid solution, in $\mathrm{mol} \mathrm{dm}^{-3}$ , given that the sodium hydroxide concentration was $0.010 \mathrm{~mol} \mathrm{dm}^{-3}$ .

$\text { « }(0.020 \times 0.010) \div 0.010=\text { » }$

0.020 «mol dm ${ }^{-3}$ »

[Maximum number: 1]

Two hydrides of nitrogen are ammonia and hydrazine, $\mathrm{N}_{2} \mathrm{H}_{4}$ . One derivative of ammonia is methanamine whose molecular structure is shown below.

Calculate, showing your working, the mass of hydrazine needed to remove all the dissolved oxygen from $1000 \mathrm{dm}^{3}$ of the sample.

Calculate the volume, in $\mathrm{dm}^{3}$ , of nitrogen formed under SATP conditions.
(The volume of 1 mol of gas $=24.8 \mathrm{dm}^{3}$ at SATP.)

\mathrm{n}(\mathrm{N_2H_4})=\mathrm{n}(\mathrm{O_2})=\frac{8.0\,\mathrm{g}}{32.00\,\mathrm{g\,mol^{-1}}}=0.25\,\mathrm{mol}

V(\mathrm{N_2})=0.25\,\mathrm{mol}\times24.8\,\mathrm{dm^3\,mol^{-1}}=6.2\,\mathrm{dm^3}

Award [1] for correct final answer.

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Covered syllabus points

Question 1

Question 2

Question 3

Question (a)

Question (i)

Question (b)

Question (i)

Question 4

Question 5

Question 6

Question 7