Estimation of pH

Method:

The whole experiment is based on computer simulation. To train our calculation skills in titration, two trials are set. One is titration between a strong acid and a strong base. The other is between a weak acid and a strong base. In this experiment, the strong acid is HCl, the strong base is NaOH and the weak acid is CH3COOH.

Strong acid and strong base

1. Set up the apparatus.
2. Measure 25ml Ba(OH)2 by pipette.
3. Transfer the Ba(OH)2 into a beaker.
4. Add Bromothymol Blue which is and indicator.
5. Add HCl into the burette.
6. Turn on the pH meter.
7. Insert the probes into the beaker.
8. Read the reading on burette.
9. Start titrating.
10. Read the final volume.
11. Remove the probes.

Weak acid and strong base

1. Set up the apparatus.
2. Measure 25ml Ba(OH)2 by pipette.
3. Transfer the Ba(OH)2 into a beaker.
4. Add Bromothymol Blue which is and indicator.
5. Add CH3COOHhe burette.
6. Turn on the pH meter.
7. Insert the probes into the beaker.
8. Read the reading on burette.
9. Start titrating.
10. Read the final volume.
11. Remove the probes.

Apparatus:

Pipette 25ml

Burette 50ml

pH meter

Beaker 80ml

Chemicals:

Barium Hydroxide, Ba(OH)2

Hydrochloric Acid, HCl

Ethanoic Acid, CH3COOH

Bromothymol Blue

Safety:

Follow the rules in the laboratory and wear the safety goggles.

Set up of apparatus:

Procedure:

Strong acid and strong base

1. I set up the apparatus.
2. I measured 25ml Ba(OH)2 by pipette.
3. I transferred the Ba(OH)2 into a beaker.
4. I added Bromothymol Blue which is and indicator.
5. I added HCl into the burette.
6. I turned on the pH meter.
7. I inserted the probes into the beaker.
8. I read the reading on burette.
9. I started titrating.
10. I read the final volume.
11. I removed the probes.

Weak acid and strong base

1. Set up the apparatus.
2. Measure 25ml Ba(OH)2 by pipette.
3. Transfer the Ba(OH)2 into a beaker.
4. Add Bromothymol Blue which is and indicator.
5. Add CH3COOHhe burette.
6. Turn on the pH meter.
7. Insert the probes into the beaker.
8. Read the reading on burette.
9. Start titrating.
10. Read the final volume.
11. Remove the probes.

Data collection:

Strong acid and strong base

Weak acid and strong base

Data processing:

Strong acid and strong base

The chemical equation for this reaction

2HCl(aq) + Ba(OH)2(aq)  BaCl2(aq) + 2H2O(l)

Weak acid and strong base

The chemical equation for this reaction

2 CH3COOH (aq) + Ba(OH)2(aq) (CH3COOH)2Ba (aq) + 2H2O(l)

Graph:

Strong acid and strong base

Screenshot of the software

 

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Graph of the pH in the beaker against volume added

Weak acid and strong base

Screenshot of the software

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Graph of the pH in the beaker against volume added

Conclusion:

The concentration of hydrochloric acid in the first trial is

The concentration of ethanoic acid in the second trial is

Evaluation and improvement:

1. As what I have discovered, all the graphs of a certain reaction in this software are the same. There is no difference in the graph if the concentration is changed. Also the graph is distinct points rather than a curve. During the experiment, sometimes failure occurred. Thus the only improvement could be done is to change another software.