In: Chemistry
You need to prepare an acetate buffer of pH 5.50 from a 0.899 M acetic acid solution and a 2.73 M KOH solution. If you have 775 mL of the acetic acid solution, how many milliliters of the KOH solution do you need to add to make a buffer of pH 5.50? The pKa of acetic acid is 4.76.
no of moles of CH3COOH = molarity * volume in L
= 0.899*0.775 = 0.696 moles
let no of moles of KOH is x
CH3COOH + KOH ---------------> CH3COOK + H2O
I 0.696 x 0
C -x -x +x
E 0.696-x 0 +x
PH = PKa + log[CH3COOK]/[CH3COOH]
5.5 = 4.76 + logx/0.696-x
logx/0.696-x = 5.5-4.76
logx/0.696-x = 0.74
x/0.696-x = 10^0.74
x/0.696-x = 5.4954
x = 5.4954*(0.696-x)
x = 0.588
no of moles of KOH = x = 0.588 moles
no of moles of KOH = molarity * volume in L
0.588 = 2.73 * volume in L
volume in L = 0.588/2.73 = 0.2154L = 215.4ml >>>>answer
volume of KOH = 215.4ml