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Difficulty: MediumSulfur Allotropes, Hydrogen Sulfide, and Sulfur(IV) Oxide
When excess hydrogen sulfide gas (H2SH_2S) reacts with sulfur(IV) oxide (SO2SO_2) according to the balanced chemical equation:
2H2S(g)+SO2(g)→3S(s)+2H2O(l)2H_2S(g) + SO_2(g) \rightarrow 3S(s) + 2H_2O(l)
What mass of elemental sulfur is precipitated when 5.6 dm35.6\text{ dm}^3 of SO2SO_2 gas at STP reacts completely?
(Molar volume of gas at STP = 22.4 dm3 mol−122.4\text{ dm}^3\text{ mol}^{-1}; Relative atomic mass: S=32S = 32)
  1. 24.0 g24.0\text{ g}Answer
  2. B
    8.0 g8.0\text{ g}
  3. C
    22.4 g22.4\text{ g}
  4. D
    16.0 g16.0\text{ g}

Answer

The mass of elemental sulfur precipitated is 24.0 g24.0\text{ g}.
First, find the moles of SO2SO_2 at STP: 5.6 dm322.4 dm3 mol−1=0.25 mol\frac{5.6\text{ dm}^3}{22.4\text{ dm}^3\text{ mol}^{-1}} = 0.25\text{ mol}. According to the balanced equation, 1 mole of SO21\text{ mole of } SO_2 produces 3 moles of S3\text{ moles of } S. Thus, 0.25 mol of SO20.25\text{ mol of } SO_2 produces 0.75 mol of S0.75\text{ mol of } S. Multiplying by the relative atomic mass of sulfur (32 g mol−132\text{ g mol}^{-1}) gives 0.75×32=24.0 g0.75 \times 32 = 24.0\text{ g}.

Step-by-Step Solution

1
Calculate the number of moles of SO2SO_2 gas reacting at STP.
Moles of SO2=Volume at STPMolar volume at STP=5.6 dm322.4 dm3 mol−1=0.25 mol\text{Moles of } SO_2 = \frac{\text{Volume at STP}}{\text{Molar volume at STP}} = \frac{5.6\text{ dm}^3}{22.4\text{ dm}^3\text{ mol}^{-1}} = 0.25\text{ mol}.
Gas volume at STP is converted to moles using the standard molar volume of 22.4 dm3 mol−122.4\text{ dm}^3\text{ mol}^{-1}.
2
Determine the mole ratio between SO2SO_2 and SS from the balanced reaction equation.
From 2H2S(g)+SO2(g)→3S(s)+2H2O(l)2H_2S(g) + SO_2(g) \rightarrow 3S(s) + 2H_2O(l), 1 mol of SO21\text{ mol of } SO_2 yields 3 mol of S3\text{ mol of } S.
Stoichiometric coefficients give the exact molar equivalence between reactants and products.
3
Calculate the moles of SS formed.
\text{Moles of } S = 0.25\text{ mol } SO_2 \times 3 = 0.75\text{ mol } S.
Multiplying moles of SO2SO_2 by the stoichiometric factor of 3 gives the moles of produced sulfur.
4
Convert the moles of sulfur to mass in grams.
\text{Mass of } S = 0.75\text{ mol} \times 32\text{ g mol}^{-1} = 24.0\text{ g}.
Mass is obtained by multiplying number of moles by relative atomic mass.

Key Concept

Gas stoichiometry at STP and redox reaction between hydrogen sulfide and sulfur(IV) oxide
Estimated Time:1m 30s
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Topics

Sulfur Allotropes, Hydrogen Sulfide, and Sulfur(IV) Oxide

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