ACTIVITY
Techniques Lab A ext: Practice with Viscous Solutions
- Check that you have the P-20 micropipet. Place a tip on the end now so you don't
forget to later.
- Dial 20 µL.
Push the plunger to the FIRST, then SECOND STOP.
NOTICE THAT THE TWO STOPS ARE VERY EASILY "FELT."
- Now dial in 2 µL.
Push the plunger to the FIRST, then SECOND STOP.
NOTICE THAT THE SECOND STOP IS DIFFICULT TO DISTINGUISH FROM THE FIRST! Why?
FOR STEP 4 YOU ARE GOING TO USE THE PIPET INCORRECTLY--THIS TIME ONLY!
- With the P-20 set to 2 µL, push the plunger to the SECOND stop
(incorrectly) and withdraw a sample of the colored glycerol solution.
 
Look at the volume of sample in the tip.
Draw an accurate picture of the tip and mark the level of the liquid in it.
- Deliver this incorrect volume to one spot on the waxed paper. Draw the actual size of
the drop:
FOR THE REST OF THE ASSIGNMENT, USE THE PIPET CORRECTLY!
- With the P-20 set to 2 µL, push the plunger correctly
to the FIRST stop and withdraw a sample of the colored glycerol solution.
Look at the volume of sample in the tip.
Draw an accurate picture of the tip and mark the level of the liquid in it.
- Deliver this correct volume to one spot on the waxed paper. Draw the actual size
of the drop:
- If this second drop is actually 2 µL, estimate how many µL are in the first
"incorrect" drop. ________
DETERMINING THE VOLUME OF SAMPLE IN "INCORRECT" DROP.
- With the P-20 still set at 2 µL, correctly
remove 2 µL from the "incorrect" drop and place it elsewhere on the
waxed paper.
- Remove a second and third 2µL sample from that original "incorrect" drop and place them along side the first. Some of you may even be able to
get a fourth 2 µL from the "incorrect" drop.
- What is your more accurate estimate of the volume of the "incorrect" drop? __________________
- If 2 µL represents a 100% sample, what percent was represented by your incorrect drop?
___________
IF THERE IS EXTRA TIME
- Use the pipet correctly to sample 4, 6 and 10 µL of glycerol sample.
Below, draw three pipet tips and indicate the volume in each. Also draw the size
of the drop as they appear on the waxed paper.
If the teacher asked you to look at a pipet tip with a small sample in it, would you
be able to guess the amount within 1 µL? What about a drop on paper? What about
an amount in a tube?
Upon completion of this lab
- Leave equipment as you found it.
- Dispose of designated materials as outlined by your instructor.
- Leave equipment as you found it.
- Check that your work station is in order.
- Wash your hands.
POST LAB:
Check with your teacher.
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