Pure water has a hydrogen ion concentration of 1 * 10-7 M and a pH of 7. A student measures a basic solution and finds that it has a hydrogen ion (H+) concentration of 1 * 10-3. Explain why the student must have made an error in her measurement.

The student must have made an error in her measurement in the concentration of hydrogen ion in the basic solution given. From her measurement, the concentration is 1 * 10-3 M. If we calculate the pH, we get:

pH = - log (1 * 10-3) = 3

A pH of 3 does not signifies a basic solution it is in the acidic range. So, the measurement is wrong.