Question

The following information is given.

Concentration of acetic acid = 1.041M Concentration of sodium acetate = 1.071M

The buffer solutions are prepared in the following manner:

* Original buffer: mixing 100 mL of acetic acid and 100 mL of sodium acetate

* 1:5 diluted buffer: mixing 40 mL of original buffer to 160mL of deonized water

* 1:50 diluted buffer: adding 20mL of the 1:5 diluted buffer solution to 180mL of distilled water

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QUESTION:

a) calculate the pH of the original buffer

b) calculate the pH of the 1:5 diluted buffer

c) calculate the pH of the 1:50 diluted buffer

d) Should pH change upon the dilution of a buffer? Explain.

PLEASE SHOW ALL WORK. I MADE MISTAKES SOMEWHERE AND I DON'T KNOW WHERE.

Thank you.

Answer 1

By definition, dilution of a buffer does not changes pH, since we only care about the ratio between acetate/acetic acid

then

pH = pKa + log(CH3COO-/CH3COOH)

pH = 4.75 + log(M1V1 / M2V2)

note that in all cases V1 = V2 since they both are in the same solution (that is, the same volume) so

pH = 4.75 + log(M1 / M2)

M1 and M2 DO change, but they will cancel each other changes since it is the same ratio

therefore

pH = 4.75+ log(1.071/1.041)

pH = 4.76233 of, a, b,c, and this proves that NO, it will not change