How to calculate the mass percentage?

Question

The quantity of atmospheric SO2(g) can be determined by reaction with H2O2(aq) according to the balanced chemical equation shown.

H2O2(aq)+SO2(g)⟶H2SO4(aq)

The amount of sulfuric acid produced can be determined by titration with sodium hydroxide of known concentration. A 647.0 gsample of air that is known to contain sulfur dioxide was reacted with excess hydrogen peroxide. Given that 18.50 mL of 0.00250 M NaOH(aq) was required to neutralize the H2SO4(aq) produced, calculate the mass percentage of SO2(g) in the air sample

Answer 1

H₂O₂(aq) + SO₂(g) ==> H₂SO₄(aq) ... balanced equation

First, we will find the moles of H₂SO₄ produced:

The reaction is H₂SO₄ + 2NaOH ==> Na₂SO₄ + 2H₂O ... balanced equation for titration of H₂SO₄

moles H₂SO₄ present: 18.50 ml NaOH x 1 L/1000 ml x 0.00250 mol/L x 1 mol H₂SO₄/2 mols NaOH =

2.3x10^-5 moles H₂SO₄

Next, we can relate the moles of H₂SO₄ to the moles of SO₂ in the original reaction:

2.3x10^-5 mols H₂SO₄ x 1 mol SO₂ / mol H₂SO₄ = 2.3x10^-5 mols SO₂ in original air sample

Now we convert mols SO₂ to grams SO₂:

2.3x10^-5 mols SO² x 64.06 g / mol = 1.48x10^-3 g SO₂

Finally, we find the mass percent of SO2 in the original sample:

1.48x10^-3 g / 647 g (x100%) = 2.29x10^-4 % = 0.000229%