Basics of Biology

Basic Chemistry For Biology

What is the pH scale?

The pH scale is the measurement of the H concentration (hydrogen ions) in an aqueous solution and is used to measure the acidity or alkalinity of that solution. The pH scale ranges from 0 to 14. A neutral solution has a pH of 7; a solution with a pH greater than 7 is basic (or alkaline), and a solution with a pH less than 7 is acidic. In other words, the lower the pH number, the more acidic the solution; the higher the pH number, the more basic the solution. As the pH scale is logarithmic, each whole number drop on the scale represents a tenfold increase in acidity (meaning the concentration of H increases tenfold), and of course, each whole number rise on the scale represents a tenfold increase in alkalinity.

pH Value

Examples of Solutions


hydrochloric acid (HCl), battery acid


stomach acid (1.0–3.0)


lemon juice (2.3)


vinegar, wine, soft drinks, beer, orange juice, some acid rain


tomatoes, grapes, bananas (4.6)


black coffee, most shaving lotions, bread, normal rainwater


urine (5–7), milk (6.6), saliva (6.2–7.4)


pure water, blood (7.3–7.5)


egg white (8), seawater (7.8–8.3)


baking soda, phosphate detergents, Clorox


soap solutions, milk of magnesia


household ammonia (10.5–11.9), nonphosphate detergents


washing soda (sodium carbonate)


hair remover, oven cleaner


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