20
Acid–Base Equilibrium: Buffers and Buffer Capacity
Data & Observations
Marin Ruiz, Ariene Smith, Zaya Shiilegdamba, Sophia Silva, Juliette Scolieri
TAs: Adam, Peyman and Ziyuan
Part%A%-%Observations%of%Buffered%and%Unbuffered%Solutions%
Solution%
pH%
Color%
[CH3COOH]%
(M)%
[CH3COO–]%
(M)%
1%
Acetic%Acid%and%Sodium%
Acetate%
4.76%
Orange%
0.495041%
0.496058%
NaOH%
4.93%
Orange%
0.360358%
0.540543%
HCl%
4.58%
Orange%
0.541521%
0.360380%
2%
Acetic%Acid%+%Methyl%
Red%
2.38%
Red%
0.976259%
0.00413326%
+%5mL%1M%NaOH%
4.16%
Light%orange%
red%
0.655674%
0.163998%
+%5mL%1M%HCl%
1.76%
red%
0.818840%
0.000831895%
3%
1M%Sodium%Acetate%+%
Methyl%Red%
9.12%
Yellow%
0.000043%
0.980349%
+%1M%NaOH%
13.21%
Yellow%
2.88528%x10%–
9%
0.819872%
+1M%HCl%
9.08%
Yellow%
0.0000333189%
0.704192%
%
Discussion%Questions:%
• Discuss the differences in the color changes when the HCl and NaOH were added to the
solution containing both acetic acid and sodium acetate compared to when they were added
to the solutions containing only acetic acid or sodium acetate.
When HCl is added (strong acid) the solution changes to more of a red color. When NaOH (strong base)
is added to the solution, a more yellow color is produced. When added to the solution containing both,
NaOH did not change the color because the solution was highly acidic. Adding more acid made the
color more red.
5
• What happened to the concentration of the acetic acid when NaOH was added to the
mixture of acetic acid and sodium acetate? Write the chemical reaction that took place
with the added base.
When NaOH was added to the acetic acid and sodium acetate solution, the concentration of the acetic
acid decreased, while the acetic acid ion increased. Overall, there was a slight increase in pH, and
therefore a slight decrease in acidity. NaOH + CH3COOH → H2O + C2H3O2
• What happened to the concentration of the acetate ion when HCl was added to the mixture
of acetic acid and sodium acetate? Write the chemical reaction that took place with the
added acid.
