Suppose a group of students put 2.92 grams of an unknown solid acid into a 250-mL volumetric flask and filled it up to the mark with deionized water. After this they pipetted out 15.75 mL of a 1.78 M NaOH(aq) solution into another 250-mL volumetric flask and filled it up to the mark with deionized water. The students were given a pH meter that was already calibrated by their teaching assistant (T.A.) and they got the following result shown in the table below. Calculate the Molarity of the unknown solid acid. Hint: You can approximate the endpoint of the titration by taking the average volume between two consecutive titrant volume reading and you can assume that it is a 1:1 stoichiometry ratio between the acid and OH-(aq). VNaOH (mL) pH VNaOH (mL) pH 0 1.97 15 3.43 1 2.05 16 3.57 2 2.12 17 3.65 3 2.20 18 3.77 4 2.29 19 3.88 5 2.38 20 4.01 6 2.47 21 4.23 7 2.58 22 4.65 8 2.69 23 5.22 9 2.78 24 8.11 10 2.89 25 10.65 11 3.00 26 10.92 12 3.11 27 11.21 13 3.22 28 11.43 14 3.31 29 11.56 Multiple choices: 1.62 x 10-2 2.61 x 10-2 9.73 x 10-1 9.34 x 10-1 2.09 x 10-2 9.51 x 10-1 1.41 x 10-2 1.86 x 10-2 1.27 x 10-2 1.05 x 10-2 2.44 x 10-2 9.91 x 10-1 2.28 x 10-2 9.14 x 10-1
Suppose a group of students put 2.92 grams of an unknown solid acid into a 250-mL volumetric flask and filled it up to the mark with deionized water. After this they pipetted out 15.75 mL of a 1.78 M NaOH(aq) solution into another 250-mL volumetric flask and filled it up to the mark with deionized water. The students were given a pH meter that was already calibrated by their teaching assistant (T.A.) and they got the following result shown in the table below. Calculate the Molarity of the unknown solid acid. Hint: You can approximate the endpoint of the titration by taking the average volume between two consecutive titrant volume reading and you can assume that it is a 1:1 stoichiometry ratio between the acid and OH-(aq).
|
VNaOH (mL) |
pH |
VNaOH (mL) |
pH |
|
0 |
1.97 |
15 |
3.43 |
|
1 |
2.05 |
16 |
3.57 |
|
2 |
2.12 |
17 |
3.65 |
|
3 |
2.20 |
18 |
3.77 |
|
4 |
2.29 |
19 |
3.88 |
|
5 |
2.38 |
20 |
4.01 |
|
6 |
2.47 |
21 |
4.23 |
|
7 |
2.58 |
22 |
4.65 |
|
8 |
2.69 |
23 |
5.22 |
|
9 |
2.78 |
24 |
8.11 |
|
10 |
2.89 |
25 |
10.65 |
|
11 |
3.00 |
26 |
10.92 |
|
12 |
3.11 |
27 |
11.21 |
|
13 |
3.22 |
28 |
11.43 |
|
14 |
3.31 |
29 |
11.56 |
Multiple choices:
|
|
1.62 x 10-2 |
|
|
2.61 x 10-2 |
|
|
9.73 x 10-1 |
|
|
9.34 x 10-1 |
|
|
2.09 x 10-2 |
|
|
9.51 x 10-1 |
|
|
1.41 x 10-2 |
|
|
1.86 x 10-2 |
|
|
1.27 x 10-2 |
|
|
1.05 x 10-2 |
|
|
2.44 x 10-2 |
|
|
9.91 x 10-1 |
|
|
2.28 x 10-2 |
|
|
9.14 x 10-1 |
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