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**1.3 Calculations involving the molar volume of gasesExample 1.7 Calculating moles from the volume of a gas**

Calculate the number of moles of N2 in 10.0 dm3 of N2 at 1 atm and 293 K.

**Solution**

24.0 dm

^{3}of N

_{2}at 1 atm and 293 K contain 1 mol of N

_{2}.

Moles of N

_{2}in 10.0 dm3 at the same temperature and pressure

The mole concept and stoichiometry 7

1 mol × 10.0 dm3 = 0.417 mol

24.0 dm3

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**Example 1.8 Calculating volumes of gases from the number of moles**

Calculate the volumes of these gases at stp:**(a) **0.005 mol of Ar, ** (b)** 50.0 g I2 vapour.**Solution****(a) **Volume occupied by 1 mol of a gas

= 22.4 dm^{3} at stp

Volume of 0.005 mol of Ar at stp

= (0.005 mol) × (22.4 dm^{3} mol−1)

= 0.112 dm^{3}

**(b) **Molar mass of I_{2} = 2 × 126.9 = 253.8 g mol−1

Moles of I_{2} = 50.0 g m/ 253.8 g mol−1

= 0.197 mol

Volume of I_{2} vapour at stp

= (0.197 mol) × (22.4 dm^{3} mol−1)

= 4.41 dm^{3}

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