In an aqueous medium Li is a better reducing agent whereas in a gaseous medium Na is a better reducing agent. Why? AND

How do we know when to use Ksp(solubility product) and when to use 1/Ksp in place of Q in the nerst equation?

Asked by SAHANA Hebsur | 13th May, 2014, 05:55: PM

Expert Answer:

Dear Sahanahebsur,

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Solution for your first query:
Ionisation energy decreases down a group. Hence for alkali metals of group I, the trend of ionisation energy is Li+ > Na+ > K+ > Rb+ > Cs+. Therefore , sodium is better reducing agent than lithium in gaseous medium.

But in aqueous medium, Lithium is as strong a reducing agent than sodium. This is due to high hydration energy of small lithium ion, which compensates for high ionisation energy. The hydration energy of alkali metal ions follows the order: Li+ > Na+ > K+ > Rb+ > Cs+ . Due to extensive hydration, Li+ ion has the highest hydration energy, as a result of which reduction potential of Li is higher than other alkali metals. Thus most powerful reducing agent in solution is lithium.


Regards

Topperlearning Team.

Answered by Prachi Sawant | 14th May, 2014, 11:06: AM