1. Solutions and Molarity

2. What is a Solution?
A Solution is a homogeneous mixture composed of two or more substances.
Example: Salt Water
(Fig 13-2, pg 469)
NaCl(s)  Na(aq) + Cl(aq)
H2O

3. Solutions Consist of Two Things
Solvent is the substance in which the solute dissolves to make the solution. (Example: Water)
Solute is the substance dissolved in a solution. (Example: Salt)
Solutions are often called Aqueous. (A solution in which the solvent is H2O.)

4. Expressing Concentrations
The quantity of solute in a specific quantity of solvent is a measurement of the Concentration of the solution.
Concentration is measured in units of Molarity.
Molarity is the ratio of solute amount (in moles) to solution volume (in liters).

5. Molarity
Molarity =
M =
What is the Molarity of a solution that has a volume of 1.5L and contains 3.5 mols of NaCl?
moles of solute
liters of solution
mol L
3.5 mols
1.5 L
= 2.33 M

6. Sample Problem #1
What is the Molarity of a solution that has a volume of 2.5L and contains 4.3 mols of NaCl?
But what if the question involved mL instead of L?
4.3 mols
2.5 L
= 1.72 M

7. Example (mL to L)
What is the Molarity of a solution that has a volume of 400mL and contains 5.2 mols of NaCl?
Now you try one!
5.2 mols |
400 mL |
1000 mL |
1 L |
= 13 M

8. Sample Problem #2
What is the Molarity of a solution that has a volume of 250mL and contains 3.8 mols of NaCl?
But what if the question involved grams instead of mols?
3.8 mols |
250 mL |
1000 mL |
1 L |
= 15.2 M

9. Example (grams to mols)
What is the Molarity of a solution that has a volume of 1.6L and contains 60 grams of NaCl?
Now you try one!
60 g NaCl |
1.6 L |
1 mol NaCl |
58.45 g NaCl |
= 0.64 M

10. Sample Problem #3
What is the Molarity of a solution that has a volume of 2.3L and contains 95 grams of NaCl?
But what if you were just given grams and mL in the question?
95 g NaCl |
2.3 L |
1 mol NaCl |
58.45 g NaCl |
= 0.71 M

11. Example (mL to L & grams to mols)
What is the Molarity of a solution that has a volume of 600 mL and contains 75 grams of NaCl?
Now you try one!
75 g NaCl |
600 mL |
1000 mL |
1 L |
1 mol NaCl |
58.45 g NaCl |
= 2.14 M

12. Sample Problem #4
What is the Molarity of a solution that has a volume of 900 mL and contains 100 grams of NaCl?
Now what if I wanted to
make my own Molarity solution?
100 g NaCl |
900 mL |
1000 mL |
1 L |
1 mol NaCl |
58.45 g NaCl |
= 1.90 M

13. Example (Solute from Molarity)
How many grams of NaCl should be added to make a 100mL flask of a 3.5 M solution?
Now you try one!
mol
NaCl
100mL | |
1 L |
1000 mL | |
1 L |
58.45 g NaCl|
1 mol NaCl|
= g
of NaCl

14. Sample Problem #5
How many grams of NaCl should be added to make a 500mL flask of a 5.4 M solution?
Can I dilute a Molarity
sol’n to make a new one?
mol
NaCl
500mL | |
1 L |
1000 mL | |
1 L |
58.45 g NaCl|
1 mol NaCl|
= g
of NaCl

15. Example of Dilutions
You obtain 50 mL of a 4 M solution of NaCl. How many mL are in the final volume of a 2 M solution of NaCl?
M1V1 = M2V2
(4M)
(50mL) =
(2M)
(?mL)
(200) =
(2)
(?mL)
Divide by 2 on both sides
100 = mL

16. Sample Problem #6
You obtain 75 mL of a 5 M solution of NaCl. How many mL are in the final volume of a 4 M solution of NaCl?
M1V1 = M2V2
(5M)
(75mL) =
(4M)
(?mL)
(375) =
(4)
(?mL)
Divide by 4 on both sides
93.75 = mL