pH in living contexts
Show on a big screenYour mouth stays near pH 7. A sweet drink lowers it. Enamel is the hard outer layer of a tooth.
- A mouth at rest sits near pH 7.
- After a sweet drink, the reading drops.
- Below about pH 5.5, tooth enamel starts to wear.
- Brushing and rinsing carry the reading back up.
Read each place and its pH. Is it fine or trouble?
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The rule
A living thing keeps its own narrow pH window. One reading can be fine in one place. It can be trouble in another.
| Place | The pH fact |
|---|---|
| Mouth | Enamel wears below pH 5.5. Bacteria make acid from sugar. |
| The body | It works in the pH range 7.0 to 7.8. |
| Rain and rivers | Rain below pH 5.6 is acid rain. It harms river life. |
| Soil | Each plant needs its own pH range. |
Stomach acid is hydrochloric acid. It helps digest food. Too much of it causes pain. An antacid is a mild base that cancels the extra acid.
A bee or nettle sting leaves an acid on the skin. Nettle leaves inject methanoic acid. A mild base gives relief, because it cancels the acid. Baking soda in water is mildly basic.
A farmer adds lime to soil that is too acidic. Lime is a base. It raises the pH.
Toothpaste is usually basic. It cancels acid left in the mouth after food.
Try the lab to finish this lesson.