(a) Starting from the definition of an acid dissociation constant, derive an equation that relates the pH of an equilibrium mixture of an acid and its conjugate base to the composition of the solution. (b) Which ionisable groups are likely to contribute to the buffering capacity of the intracellular medium at normal intracellular pH values? What other mechanisms are available for maintaining intracellular pH values at appropriate values? (c) The pKa of methanoic acid is 3.8. What ratio of methanoic acid to sodium methanoate would be necessary to give a solution of pH 4.5? (d) Methanoic acid/methanoate is going to be used as a buffer for a reaction. The unbuffered reaction at pH 4.5 results in a decrease in the pH of 2.5 units. What is the minimum concentration of the buffer needed to prevent the pH falling below 4.25?

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