IB Chemistry SL 1.5.4 Ideal Gas Equation Questions

Relate equal gas volumes at the same temperature and pressure to equal amounts, then use balanced-equation volume ratios and molar volume at STP/SATP.

Exam points

Rearrange PV=nRT to calculate pressure, volume, amount or molar mass using kelvin temperature and consistent pressure and volume units.
Use fixed-mass gas relationships and ideal-gas graphs at constant pressure or temperature, converting Celsius to kelvin.
Apply PV=nRT or a combined-gas-law ratio when gas amount or conditions change, checking units and significant figures.

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Study 1.5.4—Ideal gas equation conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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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.

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

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IB Chemistry SL 1.5.4 Ideal Gas Equation Questions question 1