Question

Use the standard reduction potentials to determine what is observed at the cathode during the electrolysis...

Use the standard reduction potentials to determine what is observed at the cathode during the electrolysis of a 1.0 M solution of KBr that contains phenolphthalein. What observation(s) is(are) made?

O2 (g) + 4H+ (aq) + 4e- --> 2H2O (l) E°​ = 1.23 V

Br2 (l) + 2e- --> 2Br​- (aq) E°​ = 1.07 V

2H2O (l) + 2e- --> H2 (g) + 2OH​- E° = -0.80 V

K+ (aq) + e- --> K(s) E°​ = -2.92 V

(A) Solid metal forms

(B) Bubbles form and a pink color appears

(C) Dark red Br2 (aq) forms.

(D) Bubbles form and the solution remains colorless.

The correct answer is B. Can someone please explain why?

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