Acids and bases transfer protons — Science, 14–17 years
Acids and bases behave differently because of how they exchange hydrogen ions in water. Science, 14–17 years.
What acids and bases do
In water, an acid donates hydrogen ions, while a base accepts them or produces hydroxide ions. The pH scale describes how acidic a solution is: lower pH means more hydrogen ions, while higher pH means fewer. This is about particles in solution, not simply whether a substance tastes sour.
Why pH and neutralisation matter
Chemists needed a way to compare solutions whose acid strength could not be judged safely by taste or appearance. When an acid and a base react, hydrogen ions and hydroxide ions can form water; this is neutralisation. Measuring pH helps control reactions and living systems, where even a small change can affect proteins and cells.
Diluting an acid
Suppose a solution has pH 3. On the pH scale, each step represents a tenfold change in hydrogen-ion concentration. Diluting it so the pH rises to 4 means the concentration has fallen by a factor of 10. A rise to pH 5 means 100 times fewer hydrogen ions than at pH 3.
The tempting mistake
Many people treat pH as an ordinary scale, so they think pH 4 is only slightly more acidic than pH 5. The numbers are logarithmic: pH 4 has ten times the hydrogen-ion concentration of pH 5. Also, never test an unknown acid or base by tasting it; corrosive substances can look harmless.
Where it is used
Swimming pools are tested so their pH stays comfortable and disinfectants work properly. Farmers test soil pH because it affects which nutrients plant roots can absorb. In the body, blood pH is kept within a narrow range; lungs and kidneys help correct changes rather than simply making blood neutral.
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