Question

In this experiment you will be measuring pH for several different solutions. A pH probe will be used rather than pH paper as it will be more accurate.

You will be testing the pH of six solutions: deionized water, 0.1 M HCl, 0.1 M HCH₃COO, 0.1 M NaCH₃COO, 0.1 M NaOH, and a buffer made by mixing equal parts of HCH₃COO and NaCH₃COO.

You will measure the pH of each solution three times:

1. Neat - just the solution
2. After the addition of 5 drops of 1 M HCl
3. After the addition of 5 drops of 1 M NaOH

HCl is a strong acid and NaOH is a strong base. You will be testing the pH of neat solutions of these substances as a point of reference.

The important observation you should focus on is the change in pH that happens between the Neat solution and the solution with added HCl as well as the pH change that between the Neat solution and the the solution with added NaOH.

Experiment:

We will assume that your pH probes are calibrated properly. Each probe will be attached to a handheld display that will report the pH of the solution being measured. It is CRITICALLY IMPORTANT that the pH probe be rinsed between different solutions. A squeeze bottle of distilled water and a beaker make this a simple process. Your instructor will demonstrate. Please be careful with the pH probes as they are fragile.

1. Each of the six solutions should be placed into large test tubes, ~1/3 full. The test tube should be large enough diameter to accommodate the pH probe and the total volume should be high enough to immerse the tip of the probe and not spill the solution. The buffer solution should be made by mixing equal volumes of acetic acid and sodium acetate solutions. Make a total volume of 50 mL. Be sure to mix the solution completely.
2. Measure the pH of each solution (neat) and record the value in the data table. Be sure to rinse the pH probe between each of the six solutions.
3. Now, add five (5) drops of 1.0 M HCl to each test tube and mix thoroughly.
4. Measure the pH of these mixtures. Record these pH values and compare the pH of the neat solutions to the pH of the mixtures after the addition of HCl.
5. Dispose of the six mixtures. They may be poured into the sink.
6. Again, fill the six large test tubes 1/3 full, one for each of the six solutions. Then, add five (5) drops of NaOH to each tube and mix thoroughly.
7. Measure the pH of these mixtures. Record these pH values and compare the pH of the neat solutions to the pH of the mixtures after the addition of NaOH.
8. Dispose of the six mixtures. They may be poured into the sink.
   1. 
      • Fill the test tube about 1/3 full • Neat = undiluted with nothing added • Buffer is made by mixing equal volumes of HCH3COO and NaCH3COO. Make at least 50 mL of buffer solution. pH Readings Solution Water 0.1 M HCI 0.1 M HCH3COO 0.1 M NaCH3COO 0.1 M NaOH Buffer Neat Add 5 drops 1 M HCI Add 5 drops 1 M NaOH
      Problems:

   2. ompare the pH of each of the neat solutions to the pH of the mixture with HCl. What do you notice?

   3. Compare the pH of each of the neat solutions to the pH of the mixture with NaOH. What do you notice?

      Your report this time is an essay that describes how a buffer works. Use data collected in this experiment to demonstrate the buffering effect. Be sure to contrast the pH with both water and the acids/ bases used in the experiment.