Question

 A 30.00 L air sample was passed through an absorption tower contained a solution of 
Cd2+
, where H2S was retained as CdS. The mixture was acidified and treated with 10.00 
mL of 0.01070 M I2. After the reaction, 
S
2- + I2 S(s) + 2I- was complete, the excess iodine was titrated with 12.85 mL of 0.01344 M thiosulphate. 
Calculate the concentration of H2S in ppm; use 1.20 g/L for the density of gas stream.