Extract from Chemistry: Chemistry Calculations Explained

Dr A Ninan Click here for more details of the book click here to buy

1.3 Calculations involving the molar volume of gases
Example 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 dm³ of N₂ at 1 atm and 293 K contain 1 mol of N₂.
Moles of N₂ 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 dm³ at stp
Volume of 0.005 mol of Ar at stp
= (0.005 mol) × (22.4 dm³ mol−1)
= 0.112 dm³

(b) Molar mass of I₂ = 2 × 126.9 = 253.8 g mol−1
Moles of I₂ = 50.0 g m/ 253.8 g mol−1

= 0.197 mol
Volume of I₂ vapour at stp
= (0.197 mol) × (22.4 dm³ mol−1)
= 4.41 dm³

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