Time of lab
Techniques Lab B, Electrolysis and Electrophoresis
Preparation before lab
- BEFORE PRINTING ACTIVITY SHEET, choose appropriate diagram, depending upon
which power supply you have (Kit 3 has the newer Fotodyne FotoForce 150).
- Set out NaCl, buffer (1X TAE), and phenol red solutions. If micropipets are in use by
another class at your school, students positioned around the classroom can serve as "pipetters."
You can also use droppers for NaCl and the phenol red.
- Set out supplies. Nothing has to be sterile. Amounts given in the labortory instructions are approximate.
What to demonstrate/explain
- Identify the parts of an electrophoresis apparatus as students label their Techniques Lab B Worksheets. Discuss relevant safety concerns.
- For reference during the lab, plastic-jacketed full page illustrations of the apparatus should be available for student use (located in notebook in Teacher's Box 1).
- This lab embodies discovery learning, so resist the urge to say too much at the outset!
- The principles of electrolysis can be demonstrated using a Hoffman apparatus
(See your chemistry teacher). H2 gas is collected at the cathode; O2 is collected at the anode.
Do appropriate chemistry tests to identify gases. It is suggested that you use sodium sulfate or sodium
carbonate as the electrolyte in the Hoffman apparatus.
- Be sure students shake up the phenol red solution before using, else the color reaction will be light.
- A drop of liquid soap wiped evenly on the inside surface of the gel box LID should minimize fogging.
- Be sure students "slosh" their gel boxes thoroughly (but carefully) in Step 9, or Step 10 won't be as dramatic. If well-mixed after Step 9, Step 10 will show a dramatic color change. At the cathode, because of the basic pH, the phenol red turns deep pink; at the anode, because of the acidic pH, the phenol red turns yellow.
- A white piece of paper underneath the gel box will help show off the color changes.
- Although lab calls for distilled water, deionized water works equally well.
- If a fuse should go out on a power supply, replace it with a new one. It's as easy as changing the batteries in a flashlight. The fuse (a 1-amp SloBlo) is at the back of the power supply.
- Chemical half-reactions are given at Step 8, but these are not appropriate for some classes.
- Red cabbage juice, that old standby, is an interesting substitute for phenol red. Experiment with other pH indicators!
- Adding buffer will stabilize the pH, and (at Step 13) you will not see the immediate color
changes witnessed at Step 10; but eventually changes in color do develop if you let the box run for 5-10 min. because the capacity of the buffer is exceeded. You might experiment with buffer capacity by having some teams add more or less buffer to their boxes.
Note: This is an engaging activity for a Parent's Night or Open House.