Chemistry Practical 7: Acids and Bases (B)
Name: Emil
Heinäaho
Group:
Philip Norrgård
Date:
1.2.2000
Assessed
criteria: Planning A and B, Data Collection, Data Analysis, Evaluation
AIMS
The aim of this particular practical was to
investigate the pH scale. The research question was: how much water should be
added to a strong acid or base to get the pH drop by one all the way to pH 7?
There was made one rough estimation that the amounts of water added would be
rather big. The key variables were the acid or base used and also the purity of
the water.
EXPERIMENTAL SET UP
The following substances and equipment were
used: HCl ( 0,1 mol/dm3 ), NaOH ( 0,1 mol/dm3 ), distilled water,
phenolphthalein, an electronical pH meter and some calibration liquids.
At first there was determined the exact pH
values of the different substances used. For ensuring the right values the
functioning of the pH meter could be tested with the help of the calibration
liquids. What was done next was that there was putted NaOH, a strong base, into
a beaker. After this the adding of distilled water was started. The adding of
the water was continued as long as the pH of the liquid went close to neutral,
pH 7. Getting to exact pH 7 is very hard so it was enough if the pH went to
about 7. The adding of the water was simply made by putting small amounts of
water and looking at the pH meter. By this method there was tried to find out
the right proportion of water to be added. This was continued until there was
noticed that the amounts of water would get too high so another method was
taken to use. Now there was taken a small amount of the basic liquid and then a
certain amount of water. From this liquid made there was again taken the same
small amount and to this was added the certain amount of water. By this the
amounts stayed quite small. After getting the pH to the wanted level the same
was repeated with HCl, the strong acid. As a help in these neutralizations
there could be used some phenolphthalein.
DATA COLLECTION
The raw data was
gotten with some minor problems. All the following tables can be found in the Appendix part. At first
there were the pHs of the substances that can be seen in the table Figure 1.
The next thing was the adding of the to NaOH. The data can be seen in the table
in Figure 2. When looking at Figure 3 there has to be remembered that on the left, NaOH + H2O-section,
the 1 ml is always taken from the weakened liquid on the line above!
|
Substance |
pH |
|
NaOH |
12,2 |
|
HCl |
1,2 |
|
H2O |
5,5 |
|
(distilled) |
|
APPENDIX
|
NaOH
+ H2O |
|
H2O |
|
|
amount |
+ |
amount |
|
|
(ml) |
|
(ml) |
pH |
|
1 |
+ |
0 |
10,2 |
|
1 |
+ |
9 |
9 |
|
- |
+ |
9 |
8,5 |
|
1 |
+ |
9 |
7,5 |
|
1 |
+ |
9 |
7,3 |
|
NaOH |
H2O |
pH |
|
(ml) |
(ml) |
|
|
2 |
0 |
12,2 |
|
2 |
1 |
12,1 |
|
0 |
1 |
12,1 |
|
0 |
2 |
12,1 |
|
0 |
3 |
11,9 |
|
0 |
3 |
11,8 |
|
0 |
6 |
11,7 |
|
0 |
6 |
11,6 |
|
0 |
9 |
11,5 |
|
0 |
9 |
11,4 |
|
0 |
12 |
11,3 |
|
0 |
12 |
11,2 |
|
0 |
15 |
11,1 |
|
0 |
15 |
11,0 |
|
0 |
240 |
10,2 |
Figure 1
Figure
3
Figure 2
|
Substance |
pH |
|
NaOH |
12,2 |
|
HCl |
1,2 |
|
H2O |
5,5 |
|
(distilled) |
|
|
NaOH
+ H2O |
|
H2O |
|
|
amount |
+ |
amount |
|
|
(ml) |
|
(ml) |
pH |
|
1 |
+ |
0 |
10,2 |
|
1 |
+ |
9 |
9 |
|
- |
+ |
9 |
8,5 |
|
1 |
+ |
9 |
7,5 |
|
1 |
+ |
9 |
7,3 |
|
NaOH |
H2O |
pH |
|
(ml) |
(ml) |
|
|
2 |
0 |
12,2 |
|
4 |
1 |
12,1 |
|
4 |
1 |
12,1 |
|
4 |
2 |
12,1 |
|
4 |
3 |
11,9 |
|
4 |
3 |
11,8 |
|
4 |
6 |
11,7 |
|
4 |
6 |
11,6 |
|
4 |
9 |
11,5 |
|
4 |
9 |
11,4 |
|
4 |
12 |
11,3 |
|
4 |
12 |
11,2 |
|
4 |
15 |
11,1 |
|
4 |
15 |
11,0 |
|
4 |
240 |
10,2 |
Figure 1
Figure
3
Figure 2