Answer:
14.1391 g
Explanation:
The pH of a solution is defined as the negative of the hydrogen ion's concentration.
Thus,
pH = - log [H⁺]
Given that:
pH = 2.85
2.85 = - log [H⁺]
So,
<u>[H⁺] = 0.0014125 M</u>
Also, benzoic acid exists in equilibrium in water as:
C₆H₅COOH ⇄ C₆H₅COO⁻ + H⁺ Ka = 6.3×10⁻⁵
The ICE table is:
C₆H₅COOH ⇄ C₆H₅COO⁻ + H⁺
At t = 0 a 0 0
At t = teq a-x x x
The expression for Ka is:
Ka = 6.3×10⁻⁵ = [C₆H₅COO⁻][H⁺] / [C₆H₅COOH]
Also,
6.3×10⁻⁵ = x.x / (a-x)
x = [H⁺] = 0.0014125 M
6.3×10⁻⁵ = (0.0014125)² / (a-0.0014125)
<u>Solving, a = 0.3308 M</u>
Given volume = 350.0 mL = 350.0×10⁻³ L
So, Moles of benzoic acid = Concentration×Volume
<u>Moles = 0.3308×350.0×10⁻³ = 0.11578 moles</u>
Mass = Molar mass × moles
Molar mass of benzoic acid = 122.12 g/mol
So,
<u>Mass = 122.12 g/mol × 0.11578 moles = 14.1391 g</u>