JEE Main 2017 · 8 Apr · Shift 1 · Chemistry Q35

ChemistrySingle correct+4 / -1Question 35 of 90

What is the standard reduction potential (E°) for $\ce{Fe^3+ -> Fe}$ ?

Given that :

$\ce{Fe^2+ + 2e- -> Fe}$ ; $E^\circ_{\ce{Fe^2+/Fe}}=-0.47$ V

$\ce{Fe^3+ + e- -> Fe^2+}$ ; $E^\circ_{\ce{Fe^3+/Fe^2+}}=+0.77$ V

−0.057 V

+0.057 V

+0.30 V

−0.30 V

Answer and worked solution

Official answer: A

Add the free energies: $\Delta G^\circ=-2F(-0.47)-F(0.77)=-3FE^\circ$ , so
$E^\circ=\frac{2(-0.47)+0.77}3=-0.057\text{ V}.$

JEE Main 2017 · 8 Apr · Shift 1, Chemistry question 35