Question

A buffer is made by dissolving H3PO4 and NaH2PO4 in water.

Answer 1

Answer:

a. NaH₂PO₄(aq) + H⁺(aq) → H₃PO₄(aq) + Na⁺(aq)

b. H₃PO₄(aq) + OH⁻(aq) → H₂PO₄⁻(aq) + H₂O(l)

Explanation:

A buffer is the mixture of a weak acid and its conjugate base or vice versa.

a. Added acid will react with NaH₂PO₄ (Conjugate base) thus:

NaH₂PO₄(aq) + H⁺(aq) → H₃PO₄(aq) + Na⁺(aq)

When all NaH₂PO₄ reacts, the solution will have just H₃PO₄ and the buffer lose its capacity.

b. In the same way, added base will react with H₃PO₄ (weak acid), thus:

H₃PO₄(aq) + OH⁻(aq) → H₂PO₄⁻(aq) + H₂O(l)

Also, when all H₃PO₄ reacts, the solution will have just H₂PO₄⁻ and the buffer lose its capacity.

I hope it helps!

Answer 2

Answer:

(a) H₃O⁺(aq) + H₂PO₄⁻(aq) ⟶ H₃PO₄(aq) + H₂O(ℓ)

(b) OH⁻(aq) + H₃O⁺(aq) ⟶ 2H₂O(ℓ)

Explanation:

The equation for your buffer equilibrium is:

H₃PO₄(aq) + H₂O(ℓ) ⇌ H₃O⁺(aq)+ H₂PO₄⁻(aq)

(a) Adding H₃O⁺

The hydronium ions react with the basic dihydrogen phosphate ions.

H₃O⁺(aq) + H₂PO₄⁻(aq) ⟶ H₃PO₄(aq) + H₂O(ℓ)

(b) Adding OH⁻

The OH⁻ ions react with the more acidic hydronium ions.

OH⁻(aq) + H₃O⁺(aq) ⟶ 2H₂O(ℓ)