Calculate the pH after 20.0% (by moles) of the benzoic acid is converted to benzoate anion by addition of a strong base. Use the dissociation equilibrium to calculate the pH. pH =

pH = 4.79

Explanation:

The equilibrium of benzoic acid, BH, is:

BH ⇄ B⁻ + H⁺

Where B⁻ is benzoate anion

Where the dissociation equilibrium, Ka, is:

Ka = 6.46x10⁻⁵ = [B⁻] [H⁺] / [BH]

If 20.0% is B⁻, 80.0% is BH, replacing:

6.46x10⁻⁵ = [20.0%] [H⁺] / [80.0%]

1.615x10⁻⁵ = [H⁺]

As pH = -log [H⁺]

in the given question, the partial pressure is calculated by using the ideal gas equation, that is, pv = nrt

here, p is pressure, v is volume = 25 l, n is number of moles = 0.0104 moles, r is gas constant = -0.0821 l.atm / mol.k

t is temperature = 273 k

p = nrt / v

p = (0.0104 mol × 0.0821 l.atm / mol.k × 273 k) / 25 l

= 0.0093 atm