In: Chemistry
The data below was obtained for titration of 25.00mL of a weak acid with 0.150 M KOH. What volume of the KOH solution is required to reach the stoichiometric point? Answer: __ __ . __ mL
VKOH added (mL) pH
0.00 1.96
2.00 2.22
4.00 2.46
7.00 2.77
10.00 3.06
12.00 3.29
14.00 3.60
16.00 4.26
17.00 11.08
18.00 11.67
20.00 12.05
25.00 12.40
The way to calculate the stoichiometric point is graphically because we have the data and we don't know which is the weak acid used.
We know that the weak acid is monoprotic because it suddenly changes once. In this change is the stoichiometric point. If we see the graphic it occurs between 16 and 17ml of KOH added.
In the graph that follow, we see that pH=7 is found at 16.4ml approx.
We know that when a strong base is added to a strong acid the stoichiometric point is at pH=7, and we also know that the pH which is found the stoichiometric point for a weak acid is higher than strong acid. For this reason, we can say that the stoichiometric point for this solution is found using 16.5ml of KOH.
Calculating the pH at stoichiometric point we have pH=7.67.