Laboratory Tests pH and the pH scale

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

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

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

The pH scale Strong alkali Strong acid Neutral 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Stomach acid Lemon juice Water Soap Baking powder Oven cleaner Strong alkali Strong acid Neutral

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

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.

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

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

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