(a) When certain buffer is made by mixing sodium formate and formic acid in water, explain how it neutralizes an addition of a small amount of an acid or a base. (b) When a basic buffer is made by mixing ammonium hydroxide and ammonium nitrate in water, explain how it resists change in its pH on addition of a small amount of an acid or a base
(a) Here, HCOO- is common ion. So when small amount of hydrogen ions are added, it combines with HCOO- which are in excess to form HCOOH and H+ remains the same. So pH remains constant. When a small amount of hydroxide ions are added, hydroxide ions take up hydrogen ions and so dissociation of HCOOH will increase so as to maintain concentration of hydroxide ions. So pH is not affected. (b) Here, ammonium ions are common ions. So when a small amount of hydrogen ions are added, hydrogen ion will take up hydroxide ion and dissociation of ammonium hydroxide will increase so as to maintain hydroxide constant. So, pH remains constant. When a small amount of hydroxide ions are added, ammonium ions which are in excess will combine with hydroxide ions to form ammonium hydroxide back so as to maintain hydroxide constant. So, pH remains constant.
