A chemistry graduate student is given 125.mL of a 0.20M acetic acid HCH3CO2 solution. Acetic acid is a weak acid with =Ka×1.810−5. What mass of NaCH3CO2 should the student dissolve in the HCH3CO2 solution to turn it into a buffer with pH =4.47?

Answer : The mass of sodium acetate is, 1.097 grams.

Explanation : Given,

The dissociation constant for acetic acid =

Concentration of acetic acid (weak acid)= 0.20 M

volume of solution = 125. mL

pH = 4.47

First we have to calculate the value of .

The expression used for the calculation of is,

Now put the value of in this expression, we get:

Now we have to calculate the concentration of sodium acetate (conjugate base or salt).

Using Henderson Hesselbach equation :

Now put all the given values in this expression, we get:

Now we have to calculate the mass of sodium acetate.

Therefore, the mass of sodium acetate is, 1.097 grams.

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