If the pH of an acid changes from 3 to 2. the concentration of hydrogen ions will increase by a factor of __ . What number completes the sentence?

The pH of a substance is, just like the last question, a measure of the hydrogen ion ( ) concentration of the solution, but is expressed as the negative logarithm to the base of ten. A smaller pH (in this case moving from 3 to 2) signifies a higher acidity or greater concentration in the solution. Hence, by decreasing the pH by one unit, you're increasing the concentration tenfold due to the ten-fold difference that exists between each unit on the pH scale.