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Work in the Laboratory Index

 

Results

Record your results a table:

 

Solution

pH

 

 

 

 

 

 

 

 

 

 

 

 

 

 

WORK IN THE LABORATORY

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Experiment to Test the pH of Different Solutions

PDF version

Introduction

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).

 

Aim

To find the pH of different solutions

 

Method

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.

 

pH testing

 

3. Remove the indicator paper and compare its colour with the appropriate colour chart.

 

pH chart key

 

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).

 

Conclusion

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.

 

Further Investigation

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.

 

Neutralization

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
Why should the pH move above pH7?
What would you now do to reach pH7?

 

Dilution

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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