The quantity of atmospheric SO_2(g) can be determined by reaction with H_2O_2(aq

Question

The quantity of atmospheric SO_2(g) can be determined by reaction with H_2O_2(aq), according to the balanced chemical equation shown below. H_2O_2(aq) + SO_2(g) rightarrow H_2SO_4(aq) amount of sulfuric acid produced can be determined by titration with sodium hydroxide of known concentration. An 542.0 gram sample of an air that is known to contain sulfur dioxide was reacted with excess hydrogen peroxide. Given that 18.50 mL of a 0.00250 M NaOH(aq) were required to neutralize the H_2SO_4(aq) produced, calculate the mass percentage of SO_2(g) in the air sample.

Explanation / Answer

We have the following reactions:

(1) SO2(g) + H2O2(aq) --> H2SO4(aq)

(2) H2SO4(aq) + 2NaOH(aq) --> Na2SO4(aq) + 2 H2O(l)

Molecular wieght [MW]

MW SO2= 64.07g/mol

Obtaining the moles of NaOH:

0.0185 L * 0.0025 M= 4.625x10-5 mol

according to the eaquation #2 we need 1 mol of H2SO4 per 2 mol NaOH:

(1 mol H2SO4/ 2 mol NaOH)* 4.625x10-5 mol NaOH = 2.3125x10-5 mol H2SO4.

According to equation #1 for each 1 mol of SO2 we obtain 1 mol of H2SO4, so the ratio is 1:1

So we have 2.3125x10-5 mol SO2, using its MW:

2.3125x10-5 mol SO2 * 64.07 g/mol = 1.4816x10-3 g of SO2

with the air mass we can calculate now the percentage of SO2:

(1.4816x10-3 g of SO2 / 542 g of air) * 100 = 0.000273 %w of SO2 in the air

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