Please answer the following questions and their parts, using correct number of s
ID: 503546 • Letter: P
Question
Please answer the following questions and their parts, using correct number of significant figures.
Determination of Ka of Acetic Acid
1. The concentration of distilled white vinegar is written as 5% (w/v) of acetic acid (CH3COOH). Convert the concentration units from % (w/v) into molarity. Express your answer in four significant figures. In other words, assume that the concentration is 5.000% (w/v).
2. Calculate the concentration of hydronium ions [H3O+] of vinegar from the measured pH values. Express your answer in two significant figures.
Measured pH of vinegar: 2.5
Explanation / Answer
1)
concentration of CH3COOH = 5 %
concentration = (w/v)% x 10 / molar mass
= 5 x 10 / 60.05
molarity = 0.8326 M
2)
pH = 2.50
[H3O+] = 10^-2.50 = 3.2 x 10^-3 M
concentration of hydronium ions [H3O+] = 3.2 x 10^-3 M
Ka = [H3O+]^2 / C
= ( 3.16 x 10^-3)^2 / 0.833
= 1.2 x 10^-5