This web page will calculate the average pKa of phenol red, using your own data.  This will allow you to know if you have made a serious error in the lab calculations.  It will not tell you where that error may have been made, but some useful hints are provided.  You will still have to show every step of the calculation, as outlined in the lab report, in order to receive credit.

To use this Calculator:

• Enter all data in the designated boxes.  Enter decimal numbers only (no scientific notation and no units).
• Press the Calculate button.
• The calculated answer will be shown below.

If your final answer doesn't match the answer calculated by the computer, then consider the following possibilities:

1. If your answer is only off by the value of only a few "doubtful digits", then you may have done the calculations correctly.  The small difference may be attributed to rounding off at each step of the calculation. (The computer does not round off during any of the intermediate steps).
2. Have you entered all of the data?
3. Did you round off to too few significant figures at some point in the calculation?

Finally, be aware the getting the correct answer doesn't necessarily mean you have done each step of the calculation correctly, or that you will have reported them adequately in your lab report.

Please contact professor Carlson if you find this useful or if there are errors in the calculations.