3.5 - Tenfold concentration changes and pH

3.5 - Tenfold concentration changes and pH

In this Higher-tier lesson, use powers of ten to compare hydrogen ion concentrations and work backwards from a concentration change to a new pH.

One pH step means a factor of ten

A tenfold increase in hydrogen ion concentration, written [H⁺], decreases pH by 1. A tenfold decrease increases pH by 1. The pH number and concentration change in opposite directions.

Relative H+ concentration rises from 1 to 10, 100 and 1000 as pH falls from 6 to 3.

The numbers in the figure are relative to pH 6, not concentrations with units. Each step multiplies the previous concentration by ten, so two steps multiply by 100, not 20.

Comparing hydrogen ion concentrations

For a difference of n whole pH units, the lower-pH solution has 10ⁿ times the H⁺ concentration of the higher-pH solution. The factor has no units.

For example, pH 4 is two units below pH 6. Its H⁺ concentration is 10 × 10 = 100 times as large.

Continue this lesson.

You’re previewing NovaLearn without an account. Create a free account to read the rest.

Create free account