Question: Based on the data for step 2 of the experiment, predict what would happen if you performed step 3 of the experiment (how many sets of three drops of each of the HCl and NaOH would be needed until the buffering capacity is lost for the two solutions). Make sure to defend your answer.

Answer the question based on the following experiment.

Evaluation of the Buffer Capacity of a 0.1M Phosphate Buffer at pH 7.4

1. To each of two clean dry 100 mL beakers add 25mL of distilled water. Measure and record the pH of each one. To one beaker, add 3 drops of 0.1 M HCl and to the other add 3 drops of 0.1M NaOH. Mix each solution and measure its pH of each. What is the pH change caused by the addition of the acid and base respectively.

2. To each of two clean, dry 100 mL beakers add 25mL of 0.1 M phosphate buffer. Measure and record the pH of each one. To one beaker, add 3 drops of 0.1 M HCl and to the other add 3 drops of 0.1 M NaOH, Mix the solutions by swirling the beakers. Measure the pH of each solution.

3. Add three more drops of HCl and NaOH to your buffer solutions and measure pH. Repeat until the buffering capacity is lost. Note the number of drops of acid or base required.

Data for step 1:

pH of water with 0 drops of HCl: 9.00
pH of water with 3 drops of HCl: 2.59
pH of water with 0 drops NaOH: 9.57
pH of water with 3 drops NaOH: 11.00

Data for step 2:

pH of phosphate buffer (0.1 M) with 0 drops HCl: 7.52
pH of phosphate buffer with 3 drops HCl: 7.31
pH of phosphate buffer with 0 drops NaOH: 7.51
pH of phosphate buffer with 3 drops NaOH: 7.70