# Review of Pipetting, Serial Dilutions and Conversions A. Review…

Review of Pipetting, Serial Dilutions and Conversions
A. Review of Pipettes (5 pts)
Purpose: The purpose of this portion of the lab is to review pipetting techniques. Pipetting accurately and precisely is a skill that laboratory scientists need to master to be successful.
Using a Micropipette – University of Leicester
Complete the following table.
Type of Pippette
P2
P20
P200
P1000
Minimum volume (L)
Maximum volume (L)
What is the first stop?
List 4 pitfalls that you should avoid when using a pippette.
Understanding Serial Dilutions (10 pts)
Purpose: The purpose of this portion of the lab is to review serial dilutions calculations.
Complete the following tables below and show all of your work:
Volume of water
0
4 mL
4 mL
4 mL
4 mL
Dilution ratio
Dilution factor
Final Concentration
What type of serial dilution is this one (X : X dilution)?
Volume of water
0
1mL
1mL
1mL
1mL
Dilution ratio
Dilution factor
Final Concentration
What type of Serial dilution is this one (X : X dilution)?
Pipette Practice (10 pts)
Compare the size of different amounts of fluid.
Distinguish between the P-20, P-200 and P-1000 micropipettes. Examine each and be able to identify each at a glance.
Now get a piece of parafilm or a weigh boat. Pipet 10 L of water onto the surface, noting how much liquid is drawn into the yellow tip.
Pipet 100L of water and lay it in a drop near the 10 L droplet, again, notice how much 100ul fills the tip. Notice the size differences?
Pipet 500L of water and lay it near the other two drops, again notice how far it fills the tip and the relative size of the droplet.
Pipet each amount into a microcentrifuge tube and notice how much each fills the tube.
Hopefully now you have developed a mental image of the scale of each amount of fluid that you might use this semester.
D. Dimensional Analysis (5 pts)
Facts to remember:
Concentration (mol/L) x volume (L) = # moles
MW (g/mole) x moles = # grams
Write a similar formula for a solution with a concentration defined by mg/mL. For example, Concentration (mg/mL) x volume
give a formula for converting weight (# grams) to number of moles.
E. Calculation Review (20 pts)
These problems are intended for you to practice conversions and calculations that are essential for success in the biochemistry lab exercises.
If a student pipets 500 l of a 3 M solution of NaCl, how many moles of NaCl does he/she have?
pipetted?
If the student places the 500L from #1 into a solution with a final volume of 1200 L. What is the final concentration of NaCl in molar? In mmolar?
If a student pipets 20L of a 10 mM solution of Tris how many moles did he/she pipet?
The Tris is deposited into a final volume of 5 mL. What is the final molar concentration of Tris?
If you pipet 15L of 0.1 M Tris into a beaker and bring the volume up to 3 mL, what is the final molar concentration of Tris?
You need to add hormone from a stock of 3 mM to your 500 mL of media to have a final concentration of 0.10 M. How much of the stock hormone do you pipet?
If your protein assay shows that you have 45 mg protein per mL and you have 800 L in the fraction from your column, what is the total amount of protein?
How many grams of NaCl (MW= 58.5 g/mol) would you dissolve in water to make a 0.5 M solution of 200 mL final volume?
How many grams of sugar (sucrose MW= 342 g/mol) are in a 100 mL aliquot of a 2 L solution of sugar at 2.5 M?
How would you prepare 100 mL of 0.4 M MgSO4 from a stock solution of 2 M MgSO4?
How do you construct a 1:10 dilution series? Explain and diagram.