Solution Worksheet Molecular Lab 431
Name____________________________
In published manuscripts, concentrations are often explained in both percentage, and molar
concentrations. Today’s worksheet will take you through how to prepare both percentage and
molar solutions.
Percentage Solutions: In published papers and other scientific literature, the concentrations of
some non-homogeneous solutes (For instance, glucose or sucrose) are expressed as a percentage
of 100 mL of solution. The concentration of solute is specified as the percentage weight per unit
volume (w/v) or percentage of volume per unit volume (v/v) depending on the nature of the
solute. The (v/v) is often used when measuring concentrations of liquid detergents.
1. (2 points) You wish to prepare the various solutions of Tween 20 detergent in water. Tween
20 is a liquid detergent. Detergent solutions are produced on a percentage of volume basis (v/v).
State how much Tween 20 is necessary (v/v) to prepare 200 mL of the following Tween 20
solutions.
a. 18% Tween 20 (v/v) ________
b. 35% Tween 20 (v/v) ________
2. (1 point) You are given a solution that has 23 mL of Triton-X detergent in 100 mL total
solution. What is the concentration (in percentage) of Triton-X in the solution?
3. (3 points) You are making some media for your bacteria. Your culture medium requires
sucrose. Please state how you would prepare the following solutions.
a. 25% (w/v) sucrose for 1 L of solution _______
b. 10 % (w/v) sucrose for 1.5 L solution ________
c. 5% (w/v) for a 2 mL solution ________
4. (1 point) If you wanted 250 mL of media that is 10% raffinose what would you do, what
would you do starting with a bottle of the powder and water?
Molar Solutions: In biology, the concentrations of solutes in solutions are expressed in molarity
(M), millimolarity (mM) or micromolarity (μM), where milli=10-3 and micro=10-6. A 1 M
solution contains 1 mole of solute in 1 liter of solution, 1mM contains 1mmole of solute in 1L of
solution, and 1uM is 1umole in 1L of solution. A mole is the number of grams of the solute that
equals its molecular (formula) weight. Remember as you work through these problems, be
aware of your units!
5. (4 points) How much of each component must you add to 500 mL to prepare a 1.25 M
solution?
a) Trizma Base (MW=121.4 g/mole) _______
b) Magnesium Sulfate (MW=120.37 g/mole) ________
c) Potassium phosphate dibasic (x6H2O) (MW=174.18g/mole)_______
d) NaCl (MW= 58 g/mole) _______
6. (2 points) Please describe for me how you would prepare the Trizma base solution from #4.
Describe briefly the procedure you would use to produce the solution if you were in the
laboratory (include what equipment you might use i.e. graduated cylinders)?
7. (1 point)You are given a stock solution of 0.15 M KCl (Potassium Chloride)? What is the
concentration of Potassium chloride in mM?
8. (3 point) What are the concentrations of each reagent in 1L of 1X PBS (Phosphate Buffered
Saline)?
80g NaCl (MW = 58g/mole)
14.4g NaH2PO4 (MW = 120 g/mole)
2.4g KH2PO4 (MW = 136 g/mole)
Dilution of Stock Solutions: Sometimes the concentration of a solution is so dilute that we
cannot weigh out the appropriate amount of material. This is because the amount of material,
solute, we need is so small that we will be unable to accurately weigh it on our balance. For
instance, we want a 0.1M NaCl solution. Therefore, we prepare a stock solution of known
concentration (For instance we prepare a 5M NaCl solution). We then determine how much of
the diluted (0.1M) solution we want, for instance 100mL. To then determine how to prepare the
diluted solution, we use the formula C1V1 = C2V2, where C1 = concentration desired (0.1M),
V1=volume desired (100mL), C2=concentration we have (5M) and V2=the volume we need to
prepare the desired solution (this is unknown). Therefore, our formula would look like
0.1M(100mL)=5M(V2)
V2=2mL
Therefore, we need 2mL of the 5M solution and 98mL water to create 100mL of 0.1M NaCl.
9. (4 point) Assume you have solution of 5M NaCl.
a. How would you prepare 10 mL of 2 M NaCl
b. 4 mL of 3 M NaCl
c. 4 mL of 75 mM NaCl
d. 30 mL of 0.5 mM NaCl
10. (1 point) Assume you have 4.5 M HCl . How would you prepare 105 mL of 0.25 M HCl.
11. (1 point) You have 50 mL of a 0.5 M NaCl solution. You wish to produce 200 mL of a 0.3
M NaCl solution. Will you be able to do this? Why or why not?
12. (2 point) You are being asked to produce 50 mL of 1 mM solution of NaCl (MW=58
g/mole). How will you do this? (Hint: you will need to first make a stock solution and then
dilute it. Be aware of your units!)