Which of the following can be mixed in solution with H2CO3 to make a buffer?A.NaHCO3B.Na2CO3C.HFD.NH3

To form a buffer solution with carbonic acid (H₂CO₃), we need to combine it with a salt that can provide its conjugate base. The most suitable option will maintain the equilibrium of the weak acid and its conjugate base.

1. Break Down the Problem

   • Identify the buffer components involving H₂CO₃.
   • Determine which substances among the given options can act as a conjugate base.

2. Relevant Concepts

   • A buffer solution typically consists of a weak acid and its conjugate base.
   • H₂CO₃ is a weak acid, and its conjugate base is HCO₃⁻ (bicarbonate ion).

3. Analysis and Detail

   • Option A: NaHCO₃ - This provides the bicarbonate ion (HCO₃⁻). When mixed with H₂CO₃, it forms a buffer system:
     $\text{H}_2\text{CO}_3 \rightleftharpoons \text{HCO}_3^- + \text{H}^+$
   • Option B: Na₂CO₃ - This provides carbonate ions (CO₃²⁻), which can react with H₂CO₃ but is not a direct conjugate base for forming a buffer with H₂CO₃.
   • Option C: HF - Hydrofluoric acid is a weak acid, not fitting for a H₂CO₃ buffer formation.
   • Option D: NH₃ - Ammonia is a weak base and does not directly relate as a conjugate base to carbonic acid.

4. Verify and Summarize

   • The only suitable choice for forming a buffer with H₂CO₃ is NaHCO₃, as it directly provides the needed bicarbonate ions to maintain the pH.

Final Answer

A. NaHCO₃