1. Making Molar Solutions
From Liquids(More accurately, from stock solutions)

2. Making molar solutions from liquids
Not all compounds are in a solid form
Acids are purchased as liquids (“stock solutions”). Yet, we still need a way to make molar solutions of these compounds.
The Procedure is similar:
Use pipette to measure moles (via volume) Use volumetric flask to measure volume
Now we use the equation McVc = MdVd
c is starting (concentrated conditions)
d is ending (dilute conditions)

3. Dilution
Adding more solvent to a “stock” solution to lower it’s molarity
McVc = MdVd
Really setting moles equal
Volume units don’t matter as long as they are the same on both sides
Demo with a colored solution what happens when you take some of it out and add water to it. What happens to the concentration of the original solution and what happens to the concentration of the new solution.

4. Serial Dilution Start with 2 drops of food coloring in 100 mL of water
Original Molarity?
2/100 = 0.02M
Take 10 mL of original, put in empty beaker, and add 90 mL of water
New Molarity?
Continue the dilution until you can’t see any more color – what is it’s molarity now?
0.02 M (10 mL) = x M (100mL)
X= M
The second dilution is
0.002 M (10 mL) = x M (100mL)
X= M
The same pattern will continue with each dilution

5. More practice problems…
If you have a 0.82 M stock solution and water,
how would you make 10 mL of a 0.5 M solution.
How would you prepare
1.5 L of a 0.10 M H2SO4 from a 16 M H2SO4?
What would be the new molarity of
125 mL of a 0.2 M HBr solution if 150 mL of water were added?
0.82 M (V1) = 0.5 M (10 mL) V1 = 6.1 mL of the 0.82 M and 3.9 M of water ( =3.9)
16 M (V1) = 0.10 M (1.5L) V1 = L which is 9.4 mL of the 16M and about 1.49 L of water
3) 0.2 M (150 mL) = M2 ( ) M2 = 0.11 M

6. Practice with dilutions
You have a 55 mL of a 4.3 M solution of CaCl2 and you add 100 mL to it. What is the new molarity?
You have a 2 M solution of AgNO3, you want to make 20 mL of 1M solution? How will you make it?
You make 40 mL of a 0.2 M solution of Na2SO4, you started with 15 mL of a stock solution. What was the molarity of the this stock?
Use M1V1 = M2V2 in all of these equations.
55 mL (4.3M) = M2 (55+100) M2 = 1.53M
2M (V1) = 1 M (20mL) V1 = 10 mL of the 2 M and 10 mL of water
M1 (15mL) = 0.2 M (40 mL) M1 = 0.53 M

7. What is the relationship between molarity and volume in dilution?
When you make a dilution what always has to happen to the molarity?
The total volume?
What does this graph look like?
By definition, in a dilution the molarity has to go down. In order for that to happen the total volume of the solution has to increase.
Volume
Molari ty

8. The Dilution formula
If we have 1 L of 3 M HCl, what is M if we dilute acid to 6 L?
M1 = 3 mol/L, V1 = 1 L, V2 = 6 L
M1V1 = M2V2, M1V1/V2 = M2
M2 = (3 mol/L x 1 L) / (6 L) = 0.5 M
Why does the formula work?
Because we are equating mol to mol:
V1 = 1 L
M1 = 3 M
V2 = 6 L
M2 = 0.5 M
M1V1 = 3 mol
M2V2 = 3 mol

9. Practice problems
Q – What volume of 0.5 M HCl can be prepared from 1 L of 12 M HCl?
M1 = 12 mol/L, V1 = 1 L, M2 = 0.5 L
M1V1 = M2V2, M1V1/M2 = V2
V2 = (12 mol/L x 1 L) / (0.5 L) = 24 L
Q – 1 L of a 3 M HCl solution is added to 0.5 L of a 2 M HCl solution. What is the final concentration of HCl? (hint: first calculate total number of moles and total number of L)
# mol = (3 mol/L)(1 L) + (2 mol/L)(0.5 L)
= 3 mol + 1 mol = 4 mol
# L = 1 L L = 1.5 L
# mol/L = 4 mol / 1.5 L = 2.67 mol/L

10. 1. How many mL of a 14 M stock solution must be used to make 250 mL of a 1.75 M solution?
2. You have 200 mL of 6.0 M HF. What concentration results if this is diluted to a total volume of 1 L?
mL of 6.0 M CuSO4 must be diluted to what final volume so that the resulting solution is 1.5 M?
4. What concentration results from mixing 400 mL of 2.0 M HCl with 600 mL of 3.0 M HCl?
5. What is the concentration of NaCl when 3 L of M NaCl are mixed with 2 L of 0.2 M NaCl?
6. What is the concentration of NaCl when 3 L of 0.5 M NaCl are mixed with 2 L of water?
7. Water is added to 4 L of 6 M antifreeze until it is 1.5 M. What is the total volume of the new solution?
8. There are 3 L of 0.2 M HF L of this is poured out, what is the concentration of the remaining HF?

11. Dilution problems (1-6, 6 two ways)1.
M1 = 14 M, V1 = ?, M2 = 1.75 M, V2 = 250 mL
V1 = M2V2 / M1 = (1.75 M)(0.250 L) / (14 M)
V1 = L = mL 2.
M1 = 6 M, V1 = 0.2 L, M2 = ?, V2 = 1 L
M2 = M1V1 / V2 = (6 M)(0.2 L) / (1 L)
M2 = 1.2 M 3.
M1 = 6 M, V1 = 100 mL, M2 = 1.5 M, V2 = ?
V2 = M1V1 / M2 = (6 M)(0.100 L) / (1.5 M)
V2 = 0.4 L or 400 mL

12. Dilution problems (4 - 6)
4. # mol = (2.0 mol/L)(0.4 L) + (3.0 mol/L)(0.6 L)
= 0.8 mol mol = 2.6 mol
# L = 0.4 L L
# mol/L = 2.6 mol / 1 L = 2.6 mol/L
5. # mol = (0.5 mol/L)(3 L) + (0.2 mol/L)(2 L)
= 1.5 mol mol = 1.9 mol
# mol/L = 1.9 mol / 5 L = 0.38 mol/L
6. # mol = (0.5 mol/L)(3 L) + (0 mol/L)(2 L)
= 1.5 mol + 0 mol = 1.5 mol
# mol/L = 1.5 mol / 5 L = 0.3 mol/L
Or, using M1V1 = M2V2,
M1 = 0.5 M, V1 = 3 L, M2 = ?, V2 = 5 L

13. Dilution problems (7, 8) 7. M1 = 6 M, V1 = 4 L, M2 = 1.5 M, V2 = ?
V2 = M1V1 / M2 = (6 M)(4 L) / (1.5 M)
V2 = 16 L
8. The concentration remains 0.2 M, both volume and moles are removed when the solution is poured out. Remember M is mol/L. Just like the density of a copper penny does not change if it is cut in half, the concentration of a solution does not change if it is cut in half.

14. Practice using a pipette
Always keep pipette vertical
To rinse: rotate pipette, take up water, expel water gently
Take up water to 0 mark. Measure 3.2 mL into 10 mL cylinder. (one per person)
If drop is hanging off, touch to cylinder
Repeat with 1.7 mL and 5.1 mL
__________________________________
If done correctly you should get 10 mL in graduated cylinder

15. Reading a pipette Identify each volume to two decimal places
(values tell you how much you have expelled)
5.00

16. Practice making molar solutions
Calculate # of mL of 1 M HCl required to make 100 mL of a 0.1 M solution of HCl
Get volumetric flask, pipette, plastic bottle, mL beaker, 50 mL beaker, eyedropper. Rinse all with tap water. Dry 50 mL beaker
Place about 20 mL of 1 M HCl in 50 mL beaker
Rinse pipette, with small amount of acid
Fill flask about 1/4 full with distilled water
Add correct amount of acid with pipette. Mix.
Add water to line (use eyedropper at the end)
Place solution in plastic bottle
Label bottle. Place at front of the room.
Rinse and return all other equipment.