Calculate Mass Percent of SO2 in the air sample

Question

Scientists determine the quantity of atmospheric sulfur dioxide (SO2 ), a large contributor to acid rain, by an indirect titration. First, a scientist collects a sample of air and reacts it with hydrogen peroxide (H2O2 ) to form a solution of sulfuric acid (H2SO4 ). Then, the amount of H2SO4 produced is determined by titration with a sodium hydroxide solution (NaOH) of known concentration.

H2O2(aq)+SO2(g)⟶H2SO4(aq)

H2SO4(aq)+2NaOH(aq)⟶2H2O(l)+Na2SO4(aq)

Suppose Lane collects a 900.0 g sample of air that is known to contain SO2 and reacts it with excess H2O2 . A volume of 18.2 mL of 0.010 M NaOH is required to neutralize the H2SO4 produced. 

Calculate the mass percent of SO2 in the air sample.

Answer 1

H₂SO₄(aq) + 2NaOH(aq)⟶2H₂O(l) + Na₂SO₄(aq)

moles NaOH used = 18.2 ml x 1 L / 1000 ml x 0.010 mol/L = 0.00182 moles NaOH

moles H₂SO₄ present = 0.00182 mols NaOH x 1 mol H₂SO₄ / 2 mols NaOH = 0.00091 moles H₂SO₄

From the first reaction of H₂O₂ + SO₂ ==> H₂SO₄ where H₂O₂ is in excess, we can find the moles of SO₂...

0.00091 moles H₂SO₄ x 1 mol SO₂ / mol H₂SO₄ = 0.00091 moles SO₂ present

molar mass SO₂ = 64.06 g/mol

mass SO₂ present = 0.0091 mols x 64.02 g / mol = 0.05829 g SO₂

Mass % SO₂ in original sample = 0.05892 g / 900.0 g (x100%) = 0.00648%