The ideal gas equation and molar volume

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$PV = nRT$ — links pressure, volume, amount and temperature of an ideal gas.

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**Standard temperature and pressure**: 273 K (0 °C) and 100 kPa.

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V_{m} = **22.7 dm³ mol⁻¹** — the volume of one mole of any ideal gas at STP.

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$n = \dfrac{V}{V_{m}}$ — divide the volume (in dm³) by 22.7.

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$V = n\,V_{m}$ — multiply the amount (mol) by 22.7 dm³ mol⁻¹.

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**Pa** (pressure), **m³** (volume) and **K** (temperature), because R = 8.31 J K⁻¹ mol⁻¹ is in SI units.

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R = **8.31 J K⁻¹ mol⁻¹** (given in the data booklet).

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**Multiply by 1000** — e.g. 101 kPa = 1.01 × 10⁵ Pa.

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**Divide by 1000** — e.g. 24.0 dm³ = 0.0240 m³.

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**Add 273** — e.g. 25 °C = 298 K.

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**At STP** use V_{m} = 22.7; at **any other conditions** use PV = nRT with SI units.

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Find n from PV = nRT, then $M = \dfrac{m}{n}$ using the sample mass.