Experiment 9 - pH, Acid-Base Indicators, Buffers

Procedure:

Part B - Acid-Base Indicators

1. Fill one buret with 0.1 M NaOH solution and another buret with 0.1 M HCl solution.
2. Transfer about 25 mL of 0.1 M HCl solution into a 125 mL erlenmeyer flask and add 3-4 drops of indicator.
3. Add the base solution to the acid solution and observe the full range of colour change of the indicator. Record the full range of change in the colour in the data sheet. (Example: red to orange.)
4. In order to measure the pH of the solution at the onset of colour change, you need to add some acid solution to the Erlenmeyer flask so that the colour of the solution reaches the in-between colour of the colour change. (Example: the in-between colour of red to orange is yellow.) This is the end point of the titration for this particular indicator.
5. Transfer a portion of the solution from the Erlenmeyer flask into a small beaker and measure the pH. Record the pH on the data sheet.
6. Repeat steps 2 to 5 for each of the indicators provided.