Physical Science / Unit 6: Solutions, Acids and Bases
6.5 The pH Scale
Notes
The pH scale (0 to 14) measures how acidic or basic a solution is.
- pH below 7 is acidic, 7 is neutral (pure water), above 7 is basic.
- Each step of 1 on the scale is a factor of 10 in hydrogen ion concentration. pH 3 is 10 times more acidic than pH 4 and 1,000 times more acidic than pH 6.
- Examples: stomach acid about 1-2, lemon juice about 2, coffee about 5, blood about 7.4, baking soda solution about 9, bleach about 13.
- pH can be measured with pH paper or a pH meter.
Practice
A solution has a pH of 2. It is:
Low pH values mean high acidity.
How many times more acidic is a solution of pH 3 than a solution of pH 5?
Two pH units is $10 \times 10 = 100$.
Pure water at room temperature has a pH of:
Pure water is neutral.
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