1. ION CONCENTRATIONS pH and pOH Calculations

2.  The pH scale is used to identify a substance as an acid or a base due to the pH value.  This scale is a measurement of the H + concentration, [H + ], in the solution.  The more H + in solution, the higher the concentration, the lower the pH.  The less H + in solution, the lower the concentraion, the higher the pH.  A pOH scale can also be thought of with the same mechanics.

3.  One solution has a [H + ] of 2.45x10 -3 and there is a second solution with a [H + ] of 1.24x10 -10. Which solution would be the stronger acid?  The first solution has a larger [H + ] so it would have a lower pH and be the stronger acid. pH = -log[H + ] pH = -log(2.45x10 -3 ) = 2.61 pH = -log(1.24x10 -10 ) = 9.91

4.  What is the pH of a substance that has a [OH - ] of 3.82x10 -8 ?  You will solve the pOH with the [OH - ]. Then pOH + pH = 14, so substract your answer from 14. pOH = -log[OH - ] pOH = -log(3.82x10 -8 ) = 7.42 pH + pOH = 14 pH = 14 – pOH pH = 14 – 7.42 = 6.58 You should not round until your final answer.

5.  When finding the [H + ] or [OH - ], you will use the antilog instead of the log. The antilog button is 10 x.  What is the [H + ] of a solution that has a pH of 8.92? [H + ] = 10 -pH [H + ] = 10 -8.92 = 1.20x10 -9 [H + ]  A solution has a pOH of 2.75 so it would have an [OH - ] of _______. [OH - ] = 10 -pOH [OH - ] = 10 -2.75 = 1.78x10 -3 [OH - ]