Question

# Hydrogen sulfide in waste water can be determined by a coulometric titration with electrically-generated iodine. The...

Hydrogen sulfide in waste water can be determined by a coulometric titration with electrically-generated iodine. The products are sulfur and iodide. A 450.0-mL sample of industrial effluent took 36.0 min 52.0 sec for complete oxidation of the hydrogen sulfide, at an average current of 65.0 mA (at a 100% current efficiency). Calculate the hydrogen sulfide concentration in ppm. Use 96,500 as Faraday's Constant. State your answer to one place after the decimal and with units.

According to Faraday’s law ,W = (ECt) / 96500

Where W = mass of metal deposited = ?

E = Equivalent weight of H2S = Molar mass / 2 = 34 / 2 = 17

C = current = 65.0 mA = 65.0x10-3 A

t = time taken = 36 min +52 s

= (36x60 s) + 52 s

= 2212 s

Plug the values we get W = 0.0253 g

Given volume , V = 450 mL = 0.450 L

So concentration of H2S = 0.0253 g / 0.450 L

= 0.056 g/L

= 56 mg/L

= 56 ppm                Since 1 ppm = 1 mg/L

Therefore the concentration of H2S is 56 ppm

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