Titration practical experiment
Determining the reacting volumes of solutions of a strong acid and a strong alkali by titration
In this practical, you will use appropriate apparatus to make and record a range of accurate measurements, including the volume of liquids. You will also determine the concentration of one of the solutions in mol/dm3 and g/dm3.
It is important to:
- make and record accurate measurements
- take account of health and safety 鈥 you must wear eye protection
This description is just one way to carry out the practical.
Aims
- Determine the reacting volumes of solutions of an acid and an alkali by titration.
- (Higher tier only) Determine the concentration of one of the solutions in mol/dm3 and g/dm3.
Planning the practical
Your plan needs to address these points:
- apparatus
- reagents
- hazards, risks and precautions
Apparatus
- burette
- pipette and filler
- conical flask and white tile
Reagents
The reagents are:
- an acid (hydrochloric, sulfuric or nitric) of unknown concentration
- sodium hydroxide solution of know concentration
- a suitable indicator 鈥 methyl orange or phenolphthalein
Hazards, risks and precautions
Identify the hazards and suggest precautions to reduce the risk of harm.
| Hazard | Possible harm | Precaution |
| Dilute sodium hydroxide solution | Causes skin and serious eye irritation | Wear gloves and eye protection, and use a pipette filler |
| Spilling hydrochloric acid while filling the burette | Causes eye irritation | Fill the burette slowly below eye level, using a funnel |
| Hazard | Dilute sodium hydroxide solution |
|---|---|
| Possible harm | Causes skin and serious eye irritation |
| Precaution | Wear gloves and eye protection, and use a pipette filler |
| Hazard | Spilling hydrochloric acid while filling the burette |
|---|---|
| Possible harm | Causes eye irritation |
| Precaution | Fill the burette slowly below eye level, using a funnel |
This table does not include all possible hazards.
Carrying out the practical
- Use the pipette and pipette filler to add 25.0 cm3 of alkali to a clean conical flask.
- Add a few drops of indicator and put the conical flask on a white tile.
- Fill the burette with hydrochloric acid and note the initial burette reading.
- Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix. Add the acid drop by drop toward the end point for accuracy.
- Stop adding the acid when the indicator first permanently changes colour. Note the final burette reading.
- Repeat steps 1 鈥 5, until you get concordant titres.
| Titration | Initial burette reading /cm3 | Final burette reading /cm3 | Titre /cm3 |
| Rough | 0.0 | 24.5 | 24.5 |
| 1 | 1.0 | 24.8 | 23.8 |
| 2 | 5.0 | 28.8 | 23.8 |
| Titration | Rough |
|---|---|
| Initial burette reading /cm3 | 0.0 |
| Final burette reading /cm3 | 24.5 |
| Titre /cm3 | 24.5 |
| Titration | 1 |
|---|---|
| Initial burette reading /cm3 | 1.0 |
| Final burette reading /cm3 | 24.8 |
| Titre /cm3 | 23.8 |
| Titration | 2 |
|---|---|
| Initial burette reading /cm3 | 5.0 |
| Final burette reading /cm3 | 28.8 |
| Titre /cm3 | 23.8 |
Analysis
- Concordant titres are within 0.2 cm3 (or sometimes 0.1 cm3) of each other. In this example the results of titration 2 and 3 are the same so these are concordant.
- Calculate the average titre. This is the volume of acid that reacts exactly with the sodium hydroxide solution of unknown concentration.
Evaluating the practical
Your evaluation should answer these questions:
- What actions were taken to make accurate measurements?
- What steps were taken to ensure safety?
Question
Describe four steps needed to obtain accurate results.
- Make sure the burette is vertical.
- Take the readings from the bottom of the meniscus.
- Add the same number of drops of indicator.
- Take readings from the bottom of the meniscus.
- Add the acid dropwise near the endpoint.
Question
Explain why a pipette is used to measure the acid, rather than a measuring cylinder.
The pipette allows the same volume of acid to be added each time, helping to make the results repeatable.