IB Chemistry SL 1.5 Ideal Gases Questions

Practise IB Chemistry SL 1.5 by using PV=nRT with consistent units, reading gas-law graphs and explaining how temperature, pressure and intermolecular forces shape gas behaviour.

Exam points

Use PV=nRT to calculate gas pressure, volume, amount or molar mass with kelvin and consistent units.
Apply P₁V₁/T₁=P₂V₂ and interpret P–V or V–T graphs for a fixed gas mass.
Use the stated molar volume to convert gas amount and volume at specified temperature and pressure conditions.
Compare gas polarity to explain low-T/high-P deviations through attractions and finite molecular volume.

Covered syllabus points

1.5.1—Ideal gas model assumptions 1.5.2—Real gases 1.5.3—Molar volume 1.5.4—Ideal gas equation

[Maximum number: 4]

Alkanes are commonly occurring organic compounds.

(a)

The first four straight chain alkanes are gases at room temperature.

Boiling points of straight chain alkanes

[ 4 ]

(i)

Calculate the volume, in $\mathrm{dm}^{3}$ , occupied by 6.45 g of propane gas at 100 kPa and $15^{\circ} \mathrm{C}$ .

[ 2 ]

$\begin{aligned} \text { « } \mathrm{Mr}\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)=44.11 » \text { « } \mathrm{n}=\infty 0.146 \text { «mol» } \text { « } \mathrm{V}=\frac{0.146 \times 8.31 \times 288}{100} \Rightarrow 3.49 \text { «dm }{ }^{3} » \end{aligned}$

Award [2] for correct final answer.

Accept answers in the range 3.49-3.59 « $d m^{3}$ ».

(ii)

Outline why the volume occupied by propane(g) at very high pressure is higher than the value calculated using PV=nRT.

[ 2 ]

[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 volume of chlorine, in $\mathrm{dm}^{3}$ , produced if the reaction is conducted at standard temperature and pressure (STP). Use section 2 of the data booklet.

V(\mathrm{Cl_2})=0.0307\,\mathrm{mol}\times22.7\,\mathrm{dm^3\,mol^{-1}}=0.697\,\mathrm{dm^3}

Accept methods employing pV = nRT.

[Maximum number: 3]

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 $400 \mathrm{~cm}^{3}$ .

Calculate the molar mass of the compound, showing your working.

$T=85+273=358\ \mathrm{K}$ $n=\frac{pV}{RT} =\frac{101\times0.400}{8.31\times358} =0.0136\ \mathrm{mol}$ $M=\frac{m}{n} =\frac{1.17}{0.0136} =86.2\ \mathrm{g\ mol^{-1}}$

Award [1 max] for correct final answer without working.

[Maximum number: 2]

Alkanes are commonly occurring organic compounds.

The first four straight chain alkanes are gases at room temperature.

Boiling points of straight chain alkanes

Outline why the volume occupied by propane(g) at very high pressure is higher than the value calculated using PV=nRT.

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Covered syllabus points

Question 1

Question (a)

Question (i)

Question (ii)

Question 2

Question 3

Question 4