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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