The pH of the benzoic acid solution prior to adding sodium benzoate is : 2.96
Given data :
pH of buffer solution = 4
concentration of benzoic acid = 0.020 M
Volume of solution = 1.5 L
Ka for Benzoic acid = 6.3 * 10⁻⁵
lets represent the reaction
C₆H₅COOH(aq) ⇄ H⁺ (aq) + C₆H₅COO⁻ (aq)
Eq concentration 0.0200 M - x x + x
where : Ka = [ H⁺ ] * [ C₆H₅COO⁻ ] / [ C₆H₅COOH ]
6.3 * 10⁻⁵ = x * x / [ 0.0200 ] ----- ( 1 )
Resolving equation 1
x = 1.09 * 10⁻³ M
Hence ; [ H⁺ ] = 1.09 * 10⁻³ M
pH of benzoic acid = -log [ H⁺ ]
= - log [ 1.09 * 10⁻³ ]
= 2.96
Hence we can conclude that The pH of the benzoic acid solution prior to adding sodium benzoate is : 2.96
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The missing data related to your question is missing below is the complete question
You are asked to pre pare a pH = 4.00 buffer starting from 1.50 L of 0.0200 M solution of benzoic acid and any amount you need of sodium benzoate
What is the pH of the benzoic acid solution prior to adding sodium benzoate
