Question

A researcher transfers a 15-mL aliquot of a base (Solution X) with unknown concentration into a beaker and adds approximately 20 mL of distilled water. The researcher then titrates the solution with 0.100 M standard HCl solution and tracks the pH of the solution during the titration with a pH meter. Equivalence point volume occurs when 25ml of HCl is added. From MaVa=MbVb, we know that the molarity of Solution X is 0.0714M.

Volume of HCl added (mL)	pH of solution
0	11.3
5	9.86
10	9.44
15	9.08
20	8.66
22	8.39
24	7.88
24.5	6.7
25	5.28
25.5	4
26	2.7
28	2.22
30	2.01
35	1.7
40	1.52
45	1.4
50	1.3

1) Which base from the list of the bases provided below was the researcher most likely given?

Provide a one or two sentence explanation of your answer.

Base Kb

NaOH Kb >>1

Ethylamine 7.4×10−4

Ammonia 1.8×10−5

Pyridine 5.6×10−8

Sodium Acetate 5.6×10−10

Sodium fluoride 1.6×10−11

Potassium sulfate 8.3×10−13

2) What would happen to the equivalence point pH if using a 0.200 M HCl solution rather than a 0.100 M HCl solution to titrate the solution?

Answer 1