The standard reduction potentials at 298 K for the following half cells are given below : \(\mathrm{Cr}_{2} \mathrm{O}_{7}{ }^{2-}+14 \mathrm{H}^{+}+6 \mathrm{e}^{-} \rightarrow 2 \mathrm{Cr}^{3+}+7 \mathrm{H}_{2} \mathrm{O}, \mathrm{E}^{\circ}=1.33 \mathrm{~V}\) \(\mathrm{Fe}^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} \rightarrow \mathrm{Fe} \quad \mathrm{E}^{\circ}=-0.04 \mathrm{~V}\) \(\mathrm{Ni}^{2+}(\mathrm{aq})+2 \mathrm{e}^{-} \rightarrow \mathrm{Ni} \quad \mathrm{E}^{\circ}=-0.25 \mathrm{~V}\) \(\mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{e}^{-} \rightarrow \mathrm{Ag} \quad \mathrm{E}^{\circ}=0.80 \mathrm{~V}\) \(\mathrm{Au}^{3+}(\mathrm{aq})+3 \mathrm{e}^{-} \rightarrow \mathrm{Au} \quad \mathrm{E}^{\circ}=1.40 \mathrm{~V}\) Consider the given electrochemical reactions, The number of metal(s) which will be oxidized be \(\mathrm{Cr}_{2} \mathrm{O}_{7}{ }^{2-}\), in aqueous solution is ______.

JEE Main · 2024 · 09 Apr 2024 · Shift 1 · Redox Reactions and Electrochemistry

The standard reduction potentials at 298 K for the following half cells are given below :

Cr_{2} O_{7}^{2 -} + 14 H^{+} + 6 e^{-} \to 2 Cr^{3 +} + 7 H_{2} O, E^{\circ} = 1.33 V

Fe^{3 +} (aq) + 3 e^{-} \to Fe E^{\circ} = - 0.04 V

Ni^{2 +} (aq) + 2 e^{-} \to Ni E^{\circ} = - 0.25 V

Ag^{+} (aq) + e^{-} \to Ag E^{\circ} = 0.80 V

Au^{3 +} (aq) + 3 e^{-} \to Au E^{\circ} = 1.40 V

Consider the given electrochemical reactions,
The number of metal(s) which will be oxidized be

Cr_{2} O_{7}^{2 -}

, in aqueous solution is ______.

Answer: 3

C r_{2} O_{7}^{2 -} / C r^{3 +}

has

E ° = + 1.33

V; it oxidises any metal whose reduction potential is below this AND whose oxidation is favourable here: Fe (

- 0.04

), Ni (

- 0.25

), Ag (

+ 0.80

) are oxidised (Au at

+ 1.40

is not). Number of metals = 3.

JEE Main · 2024 · 09 Apr 2024 · Shift 1 · Integer answer