How do you answer a long answer question on how buffer systems work?

1) First, state how the buffer is prepared by saying that an excess of acid reacts with a base (include the equation for this reaction)

b) Write the overall equation of the buffer system (remember to show it as reversible) 

c) State the effect of adding an acid to the mixture: there is an increase in H+ concentration, this reacts with the conjugate base and equilibrium shifts left

d) State the effect of adding an alkali: it reacts with H+ ions leading to a fall in H+ conc, equilibrium shifts to right to restore concentrations

n.b the Ka of the buffer system remains the same throughout all the concentration changes