Electrolysis can be used to generate Fe(VI) as FeO 4 2- , a powerful oxidant whi

Question

Electrolysis can be used to generate Fe(VI) as FeO42-, a powerful oxidant which can be used to treat hazardous waste (it can convert S2- to S2O32-, CN- to CNO-, or AsO2- to AsO43- for example).

Write a balanced oxidation half reaction for an iron anode in basic solution (i.e. the presence of hydroxide ion and water).

Write a balance reaction for

FeO42-(aq) + S2- (aq) Fe(OH)3 (s) + S2O32- (aq)

How many moles of S2- can be removed from wastewater if a current of 16.0 A is applied for 1.00 H?

What volume of wastewater containing 10.0 mM S2- can be purified in 1.00 h?

Explanation / Answer

Sulfide removal from wastewater

balanced equation under basic medium,

8FeO4^2- + 6S^2- + 23H2O --> 8Fe(OH)3 + 3S2O3^2- + 22OH-

given the current (I) of 16 A and time (t) 1.0 h

charge Q,

Q = It

    = 16 x 1h x 60 min x 60 s

    = 57600 coulombs

moles of electron available = 57600/96500 = 0.6 mol e-

for every sulfide we need 2 mole e- for removal

therefore,

moles of sulfide removed from wastewater = 0.6 mol e-/2 mol e- = 0.3 mol sulfide removed

A wastewater sample containing 10.0 mM (0.01 M) S^2- when purified for 1.0 h,

Volume of waterwater that will be purified in 1 h = 0.3 mol/0.01 M = 30 L

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