Does mass increase or decrease during physical change

The same amount of matter exists before and after the change—none is created or destroyed. This concept is called the Law of Conservation of Mass.

In a physical change, a substance's physical properties may change, but its chemical makeup does not.

Explanation:

when [oh-] is 10-5  m, and [h3o+] is 10-9  m, the poh is 5 and ph is 9. again in both cases the sum of ph and poh is 14. however, the hydrogen ion concentration is not always going to be equal to exactly 1 x 10 raised to a negative number. for example, we skipped over the value of 2.0 x 10-7.