Question

a) A buffer contains significant amounts of hydrofluoric (HF) and sodium fluoride (NaF). Write the net ionic equation showing how this buffer neutralizes added HNO3. Express your answer as a chemical equation. Identify all of the phases in your answer

b) Write the net ionic equation showing how this buffer neutralizes added KOH. Express your answer as a chemical equation. Identify all of the phases in your answer

Answer 1

Answer:-

NaF is a strong electrolyte and completely ionizes in the buffer solution as:

NaF (aq) + H₂O (l)   Na​​​​​​​⁺ (aq) + F^- (aq)

HF is a weak acid and partially ionizes into in the solution as:

HF (aq) + H₂O (l)   H​​​​​​​⁺ (aq) + F^- (aq)

Also, the formation of F^- ions due to the ionisation of NaF will decrease the dissociation of HF due to common-ion effect.

a) When an acid , HNO₃ is added in the buffer solution:-

F^- (aq) + H₃O⁺ (aq) HF (aq) + H₂O (l)

the conjugate base F^- ion neutralizes the acid, H​​​​​​​​​​​​​​​​​​​​​_{3​​​​​​​}O⁺ (aq) . The equilibrium shifts to the right , and thus increasing the concentration of HF and decreasing the concentration of F​​​​​​​^- ions. Since most of the H​​​​​​​​​​​​​​_{3​​​​​​​}O⁺ ions get neutralized , pH change hardly occurs.

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b) When an base, KOH is added in the buffer solution:-

HF (aq) + ^-OH (aq) F^- (aq) + H₂O (l)

In this reaction, the conjugate acid , HF neutralizes the base, ^-OH. The equilibrium shifts to the right and thus increasing the concentration of F^- and decreasing the concentration of HF. As, most of the base get neutralized, pH change hardly occurs.

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