Question

What substance would you add to nahco3(aq) to form a buffer solution?

Answer 1

Answer is: H₂CO₃.

This buffer is example of weak acid (H₂CO₃) and its conjugate base (HCO₃⁻).

Dissociation of carbonic acid: H₂CO₃(aq) ⇄ HCO₃⁻(aq) + H⁺(aq).

Adding acid: HCO₃⁻(aq) + H⁺(aq ⇄ H₂CO₃(aq).

A buffer can be defined as a substance that prevents the pH of a solution from changing by either releasing or absorbing H⁺ in a solution.  

Buffer is a solution that can resist pH change upon the addition of an acidic or basic components and it is able to neutralize small amounts of added acid or base, pH of the solution is relatively stable.  

Answer 2

Buffer solution is made by mixing a weak acid with its conjugate base or weak base with its conjugate acid. NaHCO₃(aq) is a conjugate salt and also a conjugate base of H₂CO₃(aq) acid. Hence H₂CO₃(aq) should be added to make the buffer solution.