Question

H2S gas burns in oxygen to yield 12.8g of SO2 gas and water at STP. What is the volume of H2S taken?

Answer 1

2 H2S + 3 O2 → 2 SO2 + 2 H2O 

(12.8 g SO2) / (64.0638 g SO2/mol) x (2 mol H2S / 2 mol SO2) x (22.414 L/mol) = 4.48 L 

Answer 2

We first write the formula for the reaction as follows :

2H₂S + 3O₂ ---> 2SO₂ + 2H₂O

The moles of SO₂ is given as :

Molar mass = 32 + 16 × 2 = 64

Moles = mass/molar mass

12.8/64 = 0.2 moles

The mole ratio of Hydrogen Sulphide to Sulphur (iv) Oxide gas is 1 : 1.

The moles of hydrogen Sulphide is thus 0.2 moles.

Molar gas volume at STP is :

1 mole of a gas = 22400 ml

The volume of Hydrogen Sulphide used is thus given by :

0.2 × 22400 = 4480 ml

This is equivalent to :

4480/1000 = 4.480 liters