Titration of a Weak Acid: Data Sheet Unknown acid: C (letter or number on the un
ID: 1070187 • Letter: T
Question
Titration of a Weak Acid: Data Sheet
Unknown acid: C (letter or number on the unknown bottle)
Mass of the Unknown acid: 0.2016g
Concentration of NaOH(aq): 0.10M
Volume NaOH added
pH
0.5
4.26
1.0
4.42
1.5
4.58
2.0
4.71
2.5
4.82
3.0
4.92
3.5
5.02
4.0
5.11
4.5
5.27
5.0
5.41
5.5
5.48
6.0
5.50
6.5
5.59
7.0
5.73
7.5
5.80
8.0
5.93
8.5
6.06
9.0
6.26
10
6.53
10.5
7.06
11
9.65
11.5
10.98
12
11.23
12.5
11.39
13
11.53
13.5
11.51
14
11.58
14.5
11.65
15
11.72
15.5
11.76
16
11.81
16.5
11.84
17
11.87
17.5
11.89
Calculate Ka for your unknown acid. If your unknown is polyprotic, calculate Ka at both the equivalence points.
(Show work)
possible answers:
Potassium hydrogen phthalate (Monoprotic) [C8H5KO4 ] Molar Mass: 204.2212 4.82 pKa= 5.4
Ascorbic acid (Monoprotic) [C6H8O6 ] Molar Mass: 176.1241 pKa= 4.3
Maleic acid (Diprotic) [C4H4O4 ] Molar Mass: 116.0722 pKa 1= 1.83, pKa2= 6.07
Calculate the initial concentration of your acid. Recall that the original volume of the solution was 0.100 L
[Acid]initial =
Using your calculated value of Ka and the initial concentration of the acid, calculate the initial pH of your acid. Set up an ICE table. You may need to use the quadratic formula.
NaOH(aq) + C8H4O4(aq) ---> NaC8H4O4(aq) + H2O(l)
Titration of a Weak Acid: Data Sheet
Unknown acid: C (letter or number on the unknown bottle)
Mass of the Unknown acid: 0.2016g
Concentration of NaOH(aq): 0.10M
Volume NaOH added
pH
0.5
4.26
1.0
4.42
1.5
4.58
2.0
4.71
2.5
4.82
3.0
4.92
3.5
5.02
4.0
5.11
4.5
5.27
5.0
5.41
5.5
5.48
6.0
5.50
6.5
5.59
7.0
5.73
7.5
5.80
8.0
5.93
8.5
6.06
9.0
6.26
10
6.53
10.5
7.06
11
9.65
11.5
10.98
12
11.23
12.5
11.39
13
11.53
13.5
11.51
14
11.58
14.5
11.65
15
11.72
15.5
11.76
16
11.81
16.5
11.84
17
11.87
17.5
11.89
Calculate Ka for your unknown acid. If your unknown is polyprotic, calculate Ka at both the equivalence points.
(Show work)
possible answers:
Potassium hydrogen phthalate (Monoprotic) [C8H5KO4 ] Molar Mass: 204.2212 4.82 pKa= 5.4
Ascorbic acid (Monoprotic) [C6H8O6 ] Molar Mass: 176.1241 pKa= 4.3
Maleic acid (Diprotic) [C4H4O4 ] Molar Mass: 116.0722 pKa 1= 1.83, pKa2= 6.07
Calculate the initial concentration of your acid. Recall that the original volume of the solution was 0.100 L
[Acid]initial =
Using your calculated value of Ka and the initial concentration of the acid, calculate the initial pH of your acid. Set up an ICE table. You may need to use the quadratic formula.
NaOH(aq) + C8H4O4(aq) ---> NaC8H4O4(aq) + H2O(l)
Explanation / Answer
Calculate Ka for your unknown acid. If your unknown is polyprotic, calculate Ka at both the equivalence points.
the drastic change in pH must be the equivalence point:
10.5 pH = 7.06 and V = 11 pH = 9.65
so
assume V = (10.5+11)/2 = 10.75 mL is the equivalence point
Half equivalence point = 1/2*V = 10.75/2 = 5.375 mL
in this point,
pH = pKa + log(A-/HA)
and A-= HA in half equivalence point
pH = pKa
at V = 5.5 mL (nearest point
pH = 5.48
then pKa = 5.48
Most likely, this is:
Potassium hydrogen phthalate (Monoprotic) [C8H5KO4 ] Molar Mass: 204.2212 4.82 pKa= 5.4
q2.
Calculate the initial concentration of your acid. Recall that the original volume of the solution was 0.100 L
[C] = mol/V
MW of C8H5KO4= 204.22
mol = mass/MW = (0.2016)/204.22 = 0.0009871 mol
M = mol/V = 0.0009871/0.1 = 0.009871 M
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