Assume that 50.0 mL of 0.100 M HCl was added to 125 mL of0.100 M sodium acetat.

Question

Assume that 50.0 mL of 0.100 M HCl was added to 125 mL of0.100 M sodium acetat. Is the resulting solution a buffer? Why orwhy not? Calculate the pH of the resulting solution. TheKa for acetic acid is 1.75 x 10-5. Promise to rate, please explain. Thanks. K8 Assume that 50.0 mL of 0.100 M HCl was added to 125 mL of0.100 M sodium acetat. Is the resulting solution a buffer? Why orwhy not? Calculate the pH of the resulting solution. TheKa for acetic acid is 1.75 x 10-5. Promise to rate, please explain. Thanks. K8

Explanation / Answer

Assume that 50 mL of 0.100 M HCl was added to 125 mL of 0.100M sodium acetate. Is the resulting solution a buffer, why or whynot?

yes it is a buffer:

50 mL of 0.100 M HCl reacts with 50 ml of 0.100 M sodium acetate tomake Acetic acid.
You have 75 mls of 0.100 M sodium acetate left over. A weak acid & its conjugate base = a buffer.
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Calculate the pH of that resulting solution.

50 mL of 0.100 M HCl = 0.005 mol Acetic acid in 175 ml of solution= 0.02857 Molar Acetic acid

75 ml of 0.100 M sodium acetate left over = 0.0075 mol acetate in175 ml solution = 0.04286 Molar acetate

acetic acid <--> H+ & acetate-

Ka = 1.75 e-5 = [H+] [0.04286] / [0.02857]

[H+] = 1.166 e-5

pH+ = 4.9 (this is 1 sig fig, if the 50 ml of acid was actually 50ml & had only one sig fig)

pH+ = 4.93 (this is 2 sig figs, I am guessing that 50 ml of acidcould have been "50. ml")

pH+ = 4.933 (this is 3 sig figs , to be used if the 50 mls acid wasactually "50.0 ml")

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