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Work in the Laboratory Index
How to work in a Science Laboratory: Laboratory Rules
WORK IN THE LABORATORY
Experiment to Test the pH of Different Solutions
The pH scale measures the acidity or the alkalinity of a substance. The pH scale goes from pH1 to pH14. pH1 is the most acid, pH14 is the most alkaline and pH 7 is neutral (neither acid nor alkaline).
To find the pH of different solutions
1. Pour a small amount of the solution to be tested into a container.
2. Take a piece of indicator paper and place one end of it into the solution. Leave for at least 30 seconds.
3. Remove the indicator paper and compare its colour with the appropriate colour chart.
4. Repeat points 1 to 3 with as many other solutions as you are provided with. Make sure that the container is washed out with distilled water and dried before you add a new solution.
5. Record your results in a results table (see results sheet on left of this page).
Which of the solutions gave an acid pH? Is this the result you expected?
Which of the solutions was alkaline? How can you relate this result to the use of the liquid?
Which of the solutions were neutral? Did you expect these results? Explain.
To answer the following questions you can either try out the procedure in the laboratory or, using your knowledge and the information given, make hypotheses about what might happen.
If a drop of alkali (pH12) is added to an acid (pH2) in a test tube you will find that, after mixing the contents of the test tube, the pH value of the acid has changed. You might read pH3. If you continue to add the alkali drop by drop, mixing and testing after every added drop, you will observe that the pH moves closer to pH7. If you are lucky you will observe a pH of 7. This is neutralization.
If you are less fortunate you will find that the pH moves above pH7
If you take 1cm3 of a pH2 acid, add 9cm3 of distilled water and mix them well, what would you expect to happen to the pH of the diluted acid? Explain your answer.
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