Experiment 19-028: An Investigation of Weak Acids, Weak Bases, and Their Salts.

This week you will explore the acid-base properties of various materials by measuring the pH of their aqueous solutions. The experimental procedure is quite straight foward, you will use two methods of differing sophistication (pH paper and a pH meter) to determine the pH of solutions of various substances. From this information it is possible to classify these substances as weak or strong acids or bases or neither.

There are a few important points for this lab. For each of the solutions you should:

1. Identify the predominant ionic/neutral species present in solution;

2. Classify these species as strong/weak/pathetically weak acids/bases (or none);

3. Predict wheter the solution should be acidic, basic or neutral;

4. Write a chemical equation to show how the solution acts as an acid or base;

5. List your experimentally found pH - is it consistent with your prediction ?

For example: NaOCl

1. Predominant species: Na⁺ and OCl^-

2. Na⁺ : neither acid nor base, OCl^- : weak base

3. Prediction: BASIC

4. OCl^-_(aq) + H₂O_(l) ---> H OCl_(aq) + OH^-_(aq)

5. Experimentally determined pH 10 (by pH paper), this is consistent with the prediction.

 

You should check the pH of the distilled water in the lab and record that in your notes.

You should complete steps 1 - 4 for each of the solutions listed on the report sheets before you experimentally determine the pH of each solution. It is recommended that you use a pencil to fill out the report sheets because some of your predictions may not be consistent with your experimental results, and you will need to revise steps 1 - 4 of your worksheets to account for the experimental pH.

Your laboratory report sheets will be due at the end of the lab period.