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The standard reduction potentials at 298...

The standard reduction potentials at 298 K for the following half reactions are given against each
`Zn^(2+) (aq) + 2de hArr Zn(s) - 0.762`
`Cr^(3+)(aq) + 3e hArr Cr(s) - 0.74`
`2H^(+)(aq) + 2e hArr H_(2)(g) 0.00`
`Fe^(3+)(aq) + e hArr Fe^(2+)(aq) 0.77`
Which is the stronger reducing agent ?

A

`Fe^(2+)(aq)`

B

`H_(2)(g)`

C

`Cr(s)`

D

`Zn(s)`

Text Solution

Verified by Experts

The correct Answer is:
D
For an element or an lon to act as a reducing agent, it should itself get oxidised. Hence, the species which has the highest negative value of reduction potential will be most easily oxidised. As `Zn^(2+)` has the highest negative value for reduction, it will have the highest positive value for oxidation and thus will be the best reducing agent among the given options.
The correct order of reducing character is :
`Zn^(2+) (E^(@)= -0.762)`
`gt Cr^(3+) (E^(@)= -0.74) gt H^(+) (E^(@)= 0)`
`gt Fe^(3+) gt (E^(@)= 0.770)`
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Knowledge Check

  • The standard reduction potential at 298K for the following half reaction are given against each Zn^(2+)(aq)+2e^(-)hArrZn(s)" "-0.762 Cr^(3+)(aq)+2e^(-)hArrCr(s)" "-0.740 2H^(+)(aq)+2e^(-)hArrH_(2)(g)" "0.000 Fe^(3+)(aq)+2e^(-)hArrFe^(2+)(aq)" "0.770 which is the strongest reducing agent

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