Problem: Current is applied to an aqueous solution of sodium sulfide. What is produced at the cathode?a) O2(g)b) H2(g)c) Na(s)d) S(s) What is produced at the anode? a) H2(g)b) S(s)c) Na(s)d) O2(g)

FREE Expert Solution

Electrolysis → passing an electric current through a solution containing ions 


Recall that the cathode is where reduction occurs while the anode is where oxidation occurs.


Since Na2S is an ionic compound, it forms ions when dissociating in water


Na2S(s)  2Na+(aq) + S2(aq)


During electrolysis, the cation is reduced/gains electrons while the anion is oxidized/loses electrons


This means:

Na+ is reduced: Na+(aq) + 1 e  Na (s); E˚ = -2.71 V

S2– is oxidized: S(s) + 2 H+ (aq) + 2 e- →  H2S (g)   E˚ = 0.14 V 

  • Oxidation: H2S (g) →  S(s) + 2 H+ (aq) + 2 e- →   E˚ = -0.14 V (change sign)
    • S2- as H2S
    • oxidation is reverse of reduction
    • The standard reduction potentials (E˚) can be found in textbooks or online
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Problem Details

Current is applied to an aqueous solution of sodium sulfide. 

What is produced at the cathode?

a) O2(g)

b) H2(g)

c) Na(s)

d) S(s) 

What is produced at the anode? 

a) H2(g)

b) S(s)

c) Na(s)

d) O2(g)


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