1. Laboratory Tests
pH and the pH scale

2. What is pH?
The pH of a solution is a measure of how acidic or alkaline it is.

3. Acids Produce H+ ions in water Taste sour Corrode metals
React with bases to form salts and water

4. Bases Produce OH- ions in water Taste bitter, chalky Are electrolytes
Feel soapy, slippery
React with acids to form salts and water

5. The pH scale Strong alkali Strong acid Neutral 1 2 3 4 5 6 7 8 9 10 1112 13 14
Stomach acid
Lemon juice
Water
Soap
Baking powder
Oven cleaner
Strong alkali
Strong acid
Neutral

6. How can we test pH? Universal Indicator solution
Universal Indicator paper
pH meter

7. Using a pH meter
A pH meter is a digital device that allows you to test the pH of a solution accurately
Before you use a pH meter you must make sure it has been calibrated using buffer solutions.

8. Buffer Solutions
A buffer solution is a solution that resists a change in pH when even when small amounts of acid or alkali are added to it.
We use buffer solutions to calibrate pH meters

9. Calibrating pH meters
It is important to make sure a pH meter is calibrated before testing samples. This makes sure that the readings you get are accurate.
To calibrate a pH meter you must:
Rinse the probe in water
Dip probe into buffer solution of known pH
Adjust pH meter so that it is at correct pH
Repeat using a number of different buffers

10. pH in waterways
You are assessing the water quality of the stream that runs through Towneley Park.
One of the tests you will be performing is a pH test.
Find out…
What the pH of a healthy stream should be
What would happen to stream if the pH got too high or too low