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Difficulty: MediumOxygen, Ozone, and Classification of Oxides

What volume of dry oxygen gas measured at STP is produced when 12.25 g12.25\text{ g} of potassium trioxochlorate(V), KClO3\text{KClO}_3, is completely decomposed by heating in the presence of manganese(IV) oxide catalyst?

[K=39.0,Cl=35.5,O=16.0,Molar volume of gas at STP=22.4 dm3mol−1][\text{K} = 39.0, \text{Cl} = 35.5, \text{O} = 16.0, \text{Molar volume of gas at STP} = 22.4\text{ dm}^3\text{mol}^{-1}]

  1. A
    2.24 dm32.24\text{ dm}^3
  2. 3.36 dm33.36\text{ dm}^3Answer
  3. C
    3.60 dm33.60\text{ dm}^3
  4. D
    6.72 dm36.72\text{ dm}^3

Answer

3.36 dm33.36\text{ dm}^3
Thermal decomposition of potassium trioxochlorate(V) follows 2KClO3→2KCl+3O22\text{KClO}_3 \rightarrow 2\text{KCl} + 3\text{O}_2. Since 12.25 g12.25\text{ g} of KClO3\text{KClO}_3 corresponds to 0.10 mol0.10\text{ mol}, the reaction yields 0.15 mol0.15\text{ mol} of O2\text{O}_2. At STP, 0.15 mol×22.4 dm3mol−1=3.36 dm30.15\text{ mol} \times 22.4\text{ dm}^3\text{mol}^{-1} = 3.36\text{ dm}^3 of oxygen gas.

Step-by-Step Solution

1
Write the balanced chemical equation for the thermal decomposition of potassium trioxochlorate(V).
2KClO3(s)→2KCl(s)+3O2(g)2\text{KClO}_3\text{(s)} \rightarrow 2\text{KCl(s)} + 3\text{O}_2\text{(g)}
Establishing the correct stoichiometric mole ratio between reactant and gaseous product is essential for calculations.
2
Calculate the molar mass of KClO3\text{KClO}_3 and determine the number of moles reacted.
Molar mass of KClO3=39.0+35.5+(3×16.0)=122.5 g mol−1\text{KClO}_3 = 39.0 + 35.5 + (3 \times 16.0) = 122.5\text{ g mol}^{-1}. Moles of KClO3=12.25 g122.5 g mol−1=0.10 mol\text{KClO}_3 = \frac{12.25\text{ g}}{122.5\text{ g mol}^{-1}} = 0.10\text{ mol}.
Mass must be converted to moles to utilize equation stoichiometry.
3
Determine the moles of O2\text{O}_2 produced using the mole ratio.
Moles of O2=0.10 mol KClO3×3 mol O22 mol KClO3=0.15 mol O2\text{O}_2 = 0.10\text{ mol KClO}_3 \times \frac{3\text{ mol O}_2}{2\text{ mol KClO}_3} = 0.15\text{ mol O}_2.
Two moles of KClO3\text{KClO}_3 yield three moles of O2\text{O}_2.
4
Calculate the volume of O2\text{O}_2 produced at STP.
\text{Volume of } \text{O}_2 = 0.15\text{ mol} \times 22.4\text{ dm}^3\text{mol}^{-1} = 3.36\text{ dm}^3$.
Multiplying the amount of gas in moles by the molar gas volume at STP gives the volume.

Key Concept

Laboratory preparation of oxygen gas via catalytic thermal decomposition of potassium trioxochlorate(V) and stoichiometric volume calculations at STP.
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Topics

Oxygen, Ozone, and Classification of Oxides

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