The quantity of atmospheric SO2(g) can be determined by reaction with H202(aq),

Question

The quantity of atmospheric SO2(g) can be determined by reaction with H202(aq), according to the balanced chemical equation shown below. H2O2(aq) SO2(g) H2SO4(aq) The amount of sulfuric acid produced can be determined by titration with sodium hydroxide of known concentration. An 503.0 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 H2SO4(aq) produced, calculate the mass percentage of SO2(g) in the air sample. Number % SO2(g)

Explanation / Answer

The reaction between NaOH and H2SO4 is :

2NaOH + H2SO4 ---> Na2SO4 + 2H2O
Therefore, 2 moles of NaOH is required to neutralize 1 mole of H2SO4.

Given that, 18.50 mL of 0.0025 M NaOH is used to neutralize H2SO4.
The no. moles of NaOH = molarity x volume in L
                      = 0.0025 mole/L x 0.0185 L
                      = 4.62 x 10-5 mol
                  
Hence, the no. moles of H2SO4 = no. moles of NaOH/2
                              = 4.62 x 10-5 mol / 2
                              = 2.3125 x 10-5 mol
                          
1 mol of H2O2 reacts with 1 mol of SO2 and produces 1 mol of H2SO4.
The reaction is :

H2O2 + SO2 ---> H2SO4

Since we have 2.3125 x 10-5 mol of H2SO4 and we must also have 2.3125 x 10-5 mol SO2.
Therefore, no. moles of SO2 = 2.3125 x 10-5 mol
Mass of SO2 present in the air = no. moles x molecular wt
                               = 2.3125 x 10-5 mol x 64g/mol
                               = 1.48 x 10-3 g
                              
Therefore, 1.48 x 10-3 g of SO2 present in 503 g of air.
mass % SO2 in air = 1.48 x 10-3 g x 100/503 g
              = 2.94 x 10-4 %

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