When tert-butyl bromide undergoes solvolysis in a mixture of methanol and water, the rate of solvolysis (measured by the rate at which bromide ions form in the mixture) increases when the percentage of water in the mixture is increased.
(a) Explain this occurrence.
(b) Provide an explanation for the observation that the rate of the SN2 reaction of ethyl chloride with potassium iodide in methanol and water decreases when the percentage of water in the mixture is increased.