pH Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of pH.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A logarithmic scale from 0 to 14 that measures the concentration of hydrogen ions in a solution, indicating how acidic or basic it is.

A number that tells you: acid (low), neutral (7), base (high).

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Each pH unit represents a 10\times change in \text{H}^+ concentration.

Common stuck point: pH 3 is 10\times more acidic than pH 4, not just 'one more.'

Worked Examples

Example 1

easy
Calculate the pH of a solution with [\text{H}^+] = 1.0 \times 10^{-4}\,\text{M}.

Solution

  1. 1
    Recall the pH formula: \text{pH} = -\log[\text{H}^+], where [\text{H}^+] is the hydrogen ion concentration in mol/L.
  2. 2
    Identify the given value: [\text{H}^+] = 1.0 \times 10^{-4}\,\text{mol/L}.
  3. 3
    Apply the formula: \text{pH} = -\log(1.0 \times 10^{-4}) = -(-4) = 4

Answer

\text{pH} = 4
The pH scale is logarithmic — each unit change in pH represents a tenfold change in hydrogen ion concentration. A pH of 4 means the solution is acidic.

Example 2

medium
A solution has pH = 9. Calculate [\text{H}^+] and [\text{OH}^-].

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

medium
What is the pH of a 0.001\,\text{M} HCl solution? (HCl is a strong acid.)

Example 2

medium
Compare a solution with pH 2 and a solution with pH 5. How many times greater is the hydrogen-ion concentration in the pH 2 solution?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

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