Lab 13 Buffers
Purpose: To test the concept of buffers.
Materials:
0.10 mol/L KH2PO4 (aq)
0.10 mol/L NaOH(aq)
0.10 mol/L HCl(aq)
0.10 mol/L NaCl(aq)
2 graduated cylinders
100 mL beaker
4 test tubes
test tube rack
dropper bottle of methyl orange
dropper bottle of phenolphthalein
Procedure:
1. Obtain 50 mL of 0.10 mol/L KH2PO4 and 29 mL of 0.10 mol/L NaOH in separate graduated
cylinders
2.
3.
4.
5.
6.
7.
8.
Pour the KH2PO4 and then the NaOH into a 100 mL beaker to prepare a buffer with a pH of 7
Pour an equal volume of the buffer into two test tubes
Add 0.10 mol/L NaCl as a control into a third and a fourth test tube until they are ¾ full.
Add two drops of methyl orange to one buffer test tube and one control test tube.
Add and count drops of 0.10 mol/L HCl until the colour changes
Repeat steps 5 and 6 with phenolphthalein and 0.10 mol/L NaOH using the other two test tubes
Dispose of all solution down the drain with running water.
Observations:
Part A:
Test tube 1
Test tube 2
Drops of HCl
Drops of NaOH
Analysis:
1.
Compare the results between the drops in the buffer and the control.
Test tube 3
Test tube 4
2.
Provide an explanation for the difference between acid required to change the indicator in the buffer and in
the control.
3.
Describe an application of a buffer solution.
4.
How is buffering action displayed on a pH curve?