For the reaction: hf(aq)h'(aq)+f(aq) determine the change in the ph (aph) for the addition of 1.75 m naf salt to a 5.45 m solution of hf, ka-7.2 x 104 note: aph phhftion phacid no ion view available hint(s)

1.4

Explanation:

Let's consider the acid-dissociation of HF.

HF(aq) ⇄ H⁺(aq) + F⁻(aq)

For a weak acid, we can calculate the concentration of H⁺ ([H⁺]) using the following expression.

H⁺ = √(Ka × Ca) = √(7.2 × 10⁻⁴ × 5.45) = 0.063 M

where,

Ka: acid-dissociation constant

Ca: concentration of the acid

The pH is

pH = -log [H⁺] = -log 0.063 = 1.2

When we add a NaF solution, we have a buffer system, formed by a weak acid (HF) and its conjugate base (F⁻ coming from NaF). We can calculate the pH of a buffer using the Henderson-Hasselbalch's equation.

pH = pKa + log ([F⁻]/[HF])

pH = 3.1 + log (1.75M/5.45M) = 2.6

The change in the pH is

ΔpH = 2.6 - 1.2 = 1.4

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