KVPY SB SX Exam 2011 Question Paper

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Question : 103 of 120

Marks: +1, -0

If

E°_{\Fe^{2+}\/\Fe}=-0.440\V

and

E°_{\Fe^{3+}\/\Fe^{2+}}=0.770

, then

E°_{\Fe^{3+}\/\Fe}

is

0.330 V
-0.037 V
-0.330 V
-1.210 V

Solution:

\table Fe^{+3} \/ Fe;Fe^{+2} + 2e^{–} → Fe, E° = - 0.44; Fe^{+3} + e^{–} → Fe^{+2}, E° = 0.770 ;----------,-------; Fe^{+3 }+ 3e^{– }→ Fe, E° = ?

E°={n_1E_1°}/n_3

={2(-0.44)+1×(0.770)}/3

={-0.88+0.770}/3

= – 0.037 volt

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