buffer is an aqueous solution that can withstand the remarkable change in the level of the ph against the addition amount of alkali or acid. there are two types of buffer solution acidic buffer and alkaline buffer. a buffer solution is a mixture of a weak acid and its conjugate alkali or vice versa. its ph barely changes when small amounts of an acid or an alkali are added to it. gillespie 2018 sodium citrate is the sodium salt of citric acid it is buffer because it contains both the weak acid which is citric acid and its salt sodium citrate .hence it acts to keep the h3o+ ion concentration and the ph constant by the addition of either a small amount of strong acid like hcl in stomach juice or strong base .if we add acid such as hydrochloric acid the equilibrium shift to the left hand side and most of the hydronium ions from the hydrochloric acid combine with citrate ions forming citric acid molecules. thus there is a little increase in the concentration of hydronium ion and the ph remains practically unchanged. rice university 2018