You are to prepare 100. mL of an acetate buffer of pH 5.00 using 1.0 M acetic ac
ID: 1045258 • Letter: Y
Question
You are to prepare 100. mL of an acetate buffer of pH 5.00 using 1.0 M acetic acid (HC2H3O2) and solid sodium acetate (NaC2H3O2). To prepare for the investigation, complete the following calculations. The pKa for HC2H3O2 is 4.75.
(a) What ratio of [NaC2H3O2] to [HC2H3O2] is required?
(b) You will want the concentrations relatively dilute, so use an acid concentration of 0.10 M. What volume of 1.0 M HC2H3O2 would be needed to prepare 100. mL of buffer with an acid concentration of 0.10 M? mL
(c) How many grams of NaC2H3O2 · 3 H2O would be needed to prepare 100. mL of buffer if the acid concentration is 0.10 M? g (
d) If you add 2.7 mL of 0.50 M NaOH to 25.0 mL of the buffer, what is the new pH?
Explanation / Answer
PH = Pka + log[NaC2H3O2]/[HC2H3O2]
5 = 4.75 +log[NaC2H3O2]/[HC2H3O2]
log[NaC2H3O2]/[HC2H3O2] = 5-4.75
log[NaC2H3O2]/[HC2H3O2] = 0.25
[NaC2H3O2]/[HC2H3O2] = 10^0.25 = 1.7782
b. M1V1 = M2V2
V1 = M2V2/M1
= 0.1*100/1 = 10ml
c. no of moles of NaC2H3O2 · 3 H2O = molarity * volume in L
= 0.1*0.1 = 0.01moles
mass of NaC2H3O2 · 3 H2O = no of moles * gram molar mass
= 0.01*136 = 1.36g
d.
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