IB Chemistry SL 1.5.4 Ideal Gas Equation

Practise applying PV = nRT and the combined gas law with disciplined unit conversion. Change Celsius to kelvin, match pressure and volume units to the chosen gas constant,…

Exam points

convert temperature to kelvin and align pressure and volume units before using PV = nRT
rearrange the ideal-gas equation to calculate amount, molar mass, pressure or volume
apply a gas percentage or changed conditions before evaluating the required quantity

[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.

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1.5.4—Ideal gas equation question 1