Core practical - investigating neutralisation
There are a number of ways that you could investigate neutralisation in Chemistry. This is an outline of the required steps to undertake one of these methods. Calcium oxide or calcium hydroxide can be used in this practical.
Aims
To investigate the change in Scale of acidity or alkalinity. A pH (power of hydrogen) value below 7 is acidic, a pH value above 7 is alkaline. when adding powdered calcium hydroxide to a fixed volume of dilute hydrochloric acid.
Apparatus
Method
- Use a measuring cylinder to add dilute hydrochloric acid to a beaker.
- Dip a clean glass rod into the contents of the beaker. Use it to transfer a drop of liquid to a piece of universal indicator paper on a white tile. Wait 30 seconds, then match the colour to a pH colour chart. Record the estimated pH.
- Add a level spatula of calcium hydroxide powder to the beaker.
- Stir thoroughly, then estimate and record the pH of the mixture (as in step 2).
- Repeat steps 3 and 4 until there are no more changes in pH.
Results
Record the results in a suitable table. For example:
| Number of spatulas added | pH of reaction mixture |
| 0 | |
| 1 |
| Number of spatulas added | 0 |
|---|---|
| pH of reaction mixture |
| Number of spatulas added | 1 |
|---|---|
| pH of reaction mixture |
Analysis
Plot a graph to show:
- pH on the vertical axis
- number of spatulas added on the horizontal axis
Make sure you choose suitable scales so that at least 50% of the graph area includes plotted points. Draw a curve of best fit through these points.
The diagram shows an example:
Question
Use the graph to estimate the number of spatulas of calcium hydroxide needed to produce a neutral solution.
Six spatulas of calcium hydroxide were needed to produce a neutral solution (pH 7).
Evaluation
Question
Suggest two ways in which more accurate results could be obtained.
You could measure the mass of calcium hydroxide powder using a balance. You could also use a pH probe and meter to measure the pH, rather than estimating it using universal indicator.
Hazards, risks and precautions
It is important in this practical activity to use appropriate apparatus and methods. This includes the safe use and careful handling of substances.
Evaluate the hazards and the precautions needed to reduce the risk of harm. For example:
| Hazard | Possible harm | Precaution |
| Hydrochloric acid | Concentrated acid is corrosive and damages skin and clothes | Use dilute hydrochloric acid |
| Calcium hydroxide powder | Causes skin irritation | Wear gloves |
| Calcium hydroxide powder | Causes serious eye damage | Wear eye protection |
| Calcium hydroxide powder | May cause respiratory irritation | Avoid making a dust |
| Hazard | Hydrochloric acid |
|---|---|
| Possible harm | Concentrated acid is corrosive and damages skin and clothes |
| Precaution | Use dilute hydrochloric acid |
| Hazard | Calcium hydroxide powder |
|---|---|
| Possible harm | Causes skin irritation |
| Precaution | Wear gloves |
| Hazard | Calcium hydroxide powder |
|---|---|
| Possible harm | Causes serious eye damage |
| Precaution | Wear eye protection |
| Hazard | Calcium hydroxide powder |
|---|---|
| Possible harm | May cause respiratory irritation |
| Precaution | Avoid making a dust |