Basics of BiologyBasic 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 |
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, bananas (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), seawater (7.8–8.3) |
9 |
baking soda, phosphate detergents, Clorox |
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 |