You need to prepare an acetate buffer of pH 6.08 from a 0.812 M acetic acid solution and a 2.07 M KOH solution. If you have 925 mL of the acetic acid solution, how many milliliters of the KOH solution do you need to add to make a bufer of pH 6.08? The pKa of acetic acid is 4.76.
apply buffer equation
pH = pKa + log(A-/HA)
substitute known values
6.08 = 4.76 + log(A-/HA)
A-/HA = 10^(6.08 -4.76) = 20.892
A-. = 20.892*HA
so...
initial mmol of acid = MV = 0.812*925 = 751.1 mmol of acid
after adding mmol of base:
mmol of base = MV = 2.07*Vbase
then
acid left = 751.1 - 2.07*Vbase
conjugate formed = 2.07*Vbase
so...
relate
A-. = 20.892*HA
2.07*Vbase = (20.892)*(751.1 - 2.07*Vbase)
2.07/20.892*Vbase = 751.1 - 2.07*Vbase
(2.07/20.892 + 2.07) * Vbase = 751.1
Vbas = 751.1 / (2.07/20.892 + 2.07) = 346.27 mL of NaOH required
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