Weak acid and strong base mean before the equilibrium

2. Given the following experimental data, calculate the molarity and the p K
a
of the
acid analyte (HA) in the titration, if the balance neutralization reaction is
HA + NaOH  NaA + H
2
O.
A pH reading of 3.65 was obtained when 13.0 mL of 0.413 M NaOH was added to
the 25.0 mL analyte.
The endpoint was achieved when 31.25 mL of NaOH had been added.
3
©2014, Carolina Biological Supply
Company

Determination of Acetic Acid Concentration in Vinegar
Using Titration
Data Tables
Data Table 1: Titration of Vinegar with Sodium Hydroxide
Vinegar Sample
1
Vinegar Sample
2
Vinegar Sample
3
Mass of Vinegar
4.90 g 5.06 g 5.01 g
Volume of Vinegar
Density = 1.005 g/mL
4.88 ml 5.03 ml 4.98 ml
Initial NaOH volume in
syringe
10 ml 9.8 ml 9.6 ml
Final NaOH volume in
syringe
6 ml 6.4 ml 5.0 ml
Volume of NaOH
Delivered
4 ml 3.4 ml 4.6 ml
Moles of NaOH
Delivered
.006 .0064 .005
Moles of Acetic Acid in
Sample
.006 .0064 .005
Mass of Acetic Acid in
Sample
.006 .0064 .005
Calculated Molarity of
Acetic Acid in the
sampled vinegar
1.23 M 1.27 M 1.00 M
Calculated Percent Mass
of Acetic Acid in
sampled vinegar
.151 % .161 % 1 %
Average Calculated
Percent Mass of Acetic
Acid in Sampled Vinegar
.437 %
4
©2014, Carolina Biological Supply
Company