Physics and Chemistry

Temperature, Measurement, and Methodology

What is the pH scale?

The pH scale is the measurement of the H1 concentration (hydrogen ions) in a solution. It is used to measure the acidity or alkalinity of a solution. The pH scale ranges from 0 to 14. A neutral solution has a pH of 7, one with a pH greater than 7 is basic, or alkaline; and one with a pH less than 7 is acidic. The lower the pH below 7, the more acidic the solution. Each whole-number drop in pH represents a tenfold increase in acidity.

pH Value Examples of Solutions
0 Hydrochloric acid (HCl), battery acid
1 Stomach acid (1.0–3.0)
2 Lemon juice (2.3)
3 Vinegar, wine, soft drinks, beer, orange juice, some acid rain
4 Tomatoes, grapes, banana (4.6)
5 Black coffee, most shaving lotions, bread, normal rainwater
6 Urine (5–7), milk (6.6), saliva (6.2–7.4)
7 Pure water, blood (7.3–7.5)
8 Egg white (8.0), seawater (7.8–8.3)
9 Baking soda, phosphate detergents, Clorox™, Tums™
10 Soap solutions, milk of magnesia
11 Household ammonia (10.5–11.9), nonphosphate detergents
12 Washing soda (sodium carbonate)
13 Hair remover, oven cleaner
14 Sodium hydroxide (NaOH)


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