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Halogen exchange reactions
Concepts tested here
- Reactivity of metal fluorides
All Questions
2012 AIPMT-MAINS 1 question
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In the replacement reaction
, the reaction will be most favourable if M happens to be:
The fluoride ion must be supplied by MF. The larger the cation, the lower the lattice energy of MF and the more ionic and available the $F^-$.
Among Li, Na, K and Rb, $Rb^+$ is the largest, so RbF gives up $F^-$ most easily; RbI formed is also the most stable iodide (large cation with large anion).
So the reaction is most favourable when M is Rb.