The pH at equivalence point is 12.46
At equivalence point, number of moles of acid, n equals number of moles of base, n'
So, n = n'
CV = C'V' where
- C = concentration of acid (HCl) = 0.0470 M,
- V = volume of acid = 16.0 mL,
- C' = concentration of base (ammonia solution) and
- V' = volume of base = 26.0 mL.
<h3>Concentration of ammonia solution</h3>
Making C' subject of the formula, we have
C' = CV/V'
Substituting the values of the variables into the equation, we have
C' = CV/V'
C' = 0.0470 M × 16.0 mL/26.0 mL
C' = 0.752 MmL/26.0 mL
C' = 0.0289 M
<h3>The concentration of acid at equivalence point</h3>
We know that the ion-product of water Kw is
Kw = [H⁺][OH⁻] = where
- [H⁺] = concentration of HCl at equivalence point,
- [OH⁻] = C' = concentration of ammonia solution = 0.0289 M and
- Kw = 1.01 × 10⁻¹⁴
Making [H⁺] subject of the formula, we have
[H⁺} = Kw/[OH⁻]
[H⁺] = 1.01 × 10⁻¹⁴/0.0289
[H⁺] = 34.95 × 10⁻¹⁴
[H⁺] = 3.495 × 10⁻¹³
<h3>pH at equivalence point</h3>
Since pH = -㏒[H⁺]
pH = -㏒[3.495 × 10⁻¹³]
pH = -㏒[3.495] + (-㏒10⁻¹³)
pH = -㏒[3.495] + [-13(-㏒10)]
pH = 13 - 0.5434
pH = 12.4566
pH ≅ 12.46
So, the pH at equivalence point is 12.46
Learn more about pH at equivalence point here:
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= 0.050 mol (NH₄)₃PO₄