Calculating pH and pOH
Next let's look at values for pH and pOH. pOH is simply the power of hydroxide ion concentration and is figured the same way as pH but using the concentration of hydroxide ion instead.) For your notes, expand the table in exercise 18a by making columns for pH and pOH.)
Significant Digits in pH
Practice - pH
I'd like you to practice calculating pH values by figuring values for the two empty columns in this table (exercise 20 in your workbook). Write the hydronium ion concentrations in scientific notation and also calculate the pH value for each. Check your answers below, then continue with the lesson.
Your answers should be as follows:
Note that each pH value has one digit to the right of the decimal point because each concentration value had one significant digit.
If your answers are not correct, get some help from the instructor.
Hydronium Ion Concentration from pH
It is also possible to run the calculations in the other direction as well. If you know the pH, you can calculate the hydrogen ion concentration. Here is how you do it. Let's say the pH is 4.3. Enter the pH value and make it negative using the +/- button. Then press the 10x button. It will probably be the 2nd function or inverse of the log button. I get 0.00005 or 5 x 10-5 M. If you don't get this value when you try it with your calculator, or if you cannot find the right buttons, check with the instructor in the lab.
Practice - pH and pOH
Once you have that calculation under control, try your hand at filling in the blank spots in this table (exercise 21 in your workbook). Check your answers below then continue with the lesson.
All concentrations are expressed in molarity.
If you had trouble with any of these, first double check your calculations to make sure you entered the values and functions correctly on your calculator. Then check with your instructor.
E-mail instructor: Eden Francis
Clackamas Community College