Formic acid, HFor, has a AT value equal to about 1.8 times 10^-4, A studem is as

Question

Formic acid, HFor, has a AT value equal to about 1.8 times 10^-4, A studem is asked to prepare a buffer having a pH of 3.55 from a solution of formic acid and a solution of sodium formate having the same molarity. How many milliliters of the NaFor solution should she add to 20. mL of the HFor solution to make the buffer? (See discussion of buffers.) ____mL. How many mL of 0.10M NaOH should the student add to 20 mL 0 10 M HFor of the wished to prepare a buffer with a pH of 3.55. the same as in Prcfclcm 4? ____mL

Explanation / Answer

Ka of formic acid = 1.8 x 10^-4

pKa = 3.74

pH = 3.55

pH = pKa + log [salt / acid]

3.55 = 3.74 + log [NaF / HF]

[NaF / HF] = 0.646

both have same molarity.

volume of HF = 20 mL

NaF / 20 = 0.646

volume of NaF added = 12.9 mL

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