Master Sheet Dilutions and Lab
Name:
1.
How many moles of NaCl are in 100 ml of a 0.5 M solution of NaCl?
2.
Suppose you took 100 ml of a 0.5 M solution of NaCl and added 900 ml of water to it.
a. Did the number of moles of NaCl change?
b.
3.
Did the molarity of the NaCl solution change?
Draw 5 ions of Na+ and 5 ions of Cl- in each of the beakers below. Then “add” 100 ml of water to the beaker
on the left, and 500 of water to the beaker on the right.
Beaker #1
a.
Beaker #2
Do both beakers have the same number of moles of NaCl?
b. Do both beakers have the same concentration of NaCl?
c. Use M = mole/L to show that M x V = # moles
d. Since the #moles in each beaker is equal, it is possible to say that M1V1 = M2V2.
The Dilution Formula
In professional laboratories, it is common to have a concentrated stock solution on hand, which lab members dilute
to the appropriate concentration for their experiments. The basic idea is this: if you take a certain volume of the
stock solution, it contains a certain number of moles of solute. If you take that number of moles of solute and put it
into a larger volume of solvent, the concentration will be lower.
The easy to memorize formula to use for dilution problems is this: M1V1 = M2V2. You can, if you prefer, think of it
as McVc = MdVd where c= concentrated and d = dilute. Volume can be in any unit of volume as long as it is the same
on both sides so it will cancel.
Example:
Herkimeria had a stock solution of 10 M NaOH and needed 150 ml of 0.10 M NaOH. How much of the 10 M NaOH
does she need?
What do you know? M1 = 10 M NaOH
V1 = ???,
M2 = 0.10 M NaOH,
V2 = 150 ml
Plug into the equation and do the algebra to solve for V1.
(10 M) V1 = (0.10 M) (150 ml)
V1 = 1.5 ml
Herkimeria should take 1.5 ml of the 10 M NaOH stock and dilute it to 150 ml in order to make the 0.10 M
solution.
Lab Dilution
Your lab group must make 100.00 mL of a
provided in front of the classroom.
M Blue Dye #1 solution using the 1.0 M stock solution
Calculations
1. Using the dilution formula, calculate the number of mL of your stock solution you need to make the dilution
solution. EVERYONE MUST DO THIS CALCULATION, REGARDLESS OF WHETHER OR NOT YOU ACTUALLY
MAKE THE SOLUTION.
2.
3.
4.
5.
Obtain approximately 25 mL of the stock solution in a small beaker and bring it back to your table.
Using the appropriate pipet, measure out the amount of stock solution you calculated above.
Using the funnel, put the measured amount of stock solution into the volumetric flask.
Fill to the line with the dH2O squirt bottle, being careful not to overfill. IF YOU OVERFILL, YOU MUST POUR
OUT THE SOLUTION AND START OVER AGAIN. Put the cap (or parafilm) on and invert the flask several
times. Compare the color to your stock solution.
Label your beaker containing stock solution with its molarity. In the last 5 minutes of class, bring your beaker to the
front of the room. All beakers must be arranged in order of increasing concentration.
Questions – show calculations where appropriate.
1. Write the formulas for molarity and dilution.
2. Draw a beaker, a graduated cylinder, a pipet, and a volumetric flask. Compare the uses of each.
3. Explain the pattern you saw in all of the stock solutions arranged on the demonstration table.
4. Calculate the number of grams required to make 100 mL of a 4.5 M solution of CuSO4·5 H2O.
5. How many mL of a stock solution of 2.0 M NaCl would be needed to make 100 mL of a 0.75 M solution?
6. Write a sentence explaining how you would make the solution in #5.
TEACHER NOTES
Stock M 0.01
Mass
0.25
(g)
Dilution 0.001
M
0.02
0.5
0.04
1.0
0.06
1.5
0.08
2.0
0.1
2.5
0.2
5
0.3
7.5
0.002
0.004
0.006
0.008
0.01
0.02
0.03
Each dilution requires 10 mL of stock to dilute
**2016: a student is allergic to sulfate. Make a solution of blue dye to substitute for copper sulfate.
Molarity
# mL
0.015
1.5
0.005
.5
0.03
3
0.05
5
0.07
7
0.085
8.5
Have pipets, green pipetters, small beakers, volumetric flasks, water bottles, stock blue solution (randomly made;
not measured)