Answer:
I. A polyprotic, weak acid
II. Na2HPO4
Explanation:
Buffer solutions are those that, upon the addition of an acid or base, are capable of reacting by opposing the part of the basic or acid component to keep the pH fixed.
Buffers consist of hydrolytically active salts that dissolve in water. The ions of these salts are combined with acids and alkalis. These hydrolytically active salts are the products that result from the reaction between weak acids and strong alkalis such as calcium carbonate (from carbonic acid and calcium hydroxide) or between strong acids and weak alkalis such as ammonium chloride (a from hydrochloric acid and ammonium hydroxide).
A buffer acid reacts when a weak acid or weak base is combined with its corresponding hydrolytic salt in a water solution, a buffer system called a buffer is formed. As in this case a weak polyrotic acid with Na2HPO4, which allows the solution to be maintained at a pH of 3.8 against small aggregate amounts of both acid and base, thus favoring the reaction at a pH of 3.8
A buffer system is not always appropriate, because the ions of some hydrolytic salts can, for example, damage organisms that come into contact with it.
