Indicators and pH meters
Materials
1.
2.
3.
4.
5.
6.
pH meter or paper
2 Buret
2 Buret clamp
Two 100 mL beakers
Two 50 mL beakers
HCl solution of the following concentrations:
1.0 M, 0.1 M (1-2 L), 0.01 M, 0.001 M (Don’t need as much)
7. NaOH solution of the following concentrations:
1,0 M, 0.1 M, (500 ml) 0.01 M, 0.001 M (Don’t need as much)
8. Acid-base indicators:
phenolphthalein, methyl orange, bromothymol blue, bromocresol green, phenol red
9. Vinegar Coca-cola Windex
Procedure:
Part A - pH of Common Substances
1. Measure the pH of the basic solutions provided as on the data sheet. Use litmus pH paper.
Observations:
Acidic
Solution
pH
1.0 mol/L HCl
0.1 mol/L HCl
0.01 mol/L HDl
0.001 mol/L
HCl
Basic
Solution
pH
1.0 mol/L
NaOH
0.1 mol/L
NaOH
0.01 mol/L
NaOH
0.001 mol/L
NaOH
Household
solution
pH
Vinegar
Pop
Windex
Part B - Acid-Base Indicators
1. Fill one buret with 0.1 M NaOH solution.
2. Transfer about 25 mL of 0.1 M HCl solution into a 100 ml beaker 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.
6. Repeat steps 2 to 5 for each of the indicators provided.
Indicator
bromothymol
blue
Methyl orange
Phenol red
Phenolphthalein
Methyl violet
Initial colour
Intermediate
colour
Final colour
pH at endpoint