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Alkali Metals: Hydration of Ions
Concepts tested here
- Hydrated radius and ionic mobility
All Questions
2008 AIPMT 1 question
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The sequence of ionic mobility in aqueous solutions is -Smaller the size of the cation, higher is its charge density and higher will be its hydration.
Extent of hydration: $Na^+ \gt K^+ \gt Rb^+ \gt Cs^+$
A more heavily hydrated ion carries a larger shell of water molecules, so its effective (hydrated) size increases.
Hydrated radius: $Na^+(aq) \gt K^+(aq) \gt Rb^+(aq) \gt Cs^+(aq)$
A bigger hydrated ion moves more slowly, so its mobility in aqueous solution decreases.
Hence the ionic mobility follows the sequence: $Cs^+ \gt Rb^+ \gt K^+ \gt Na^+$