1. Solution Concentration

2. Review A solution is a homogeneous mixture.
The solvent is the major component of the solution.
The solute is the minor component and active ingredient.
A saturated solution holds the maximum amount of solute that is theoretically possible for a given temperature.

3. How would you describe this picture?

4. Solution Concentration
Is one glass of tea stronger than the other?
What’s true about the “stronger” glass of tea?
How much tea does it have in it compared to the other glass?

5. Solution Concentration
Concentration – a ratio comparing the amount of solute to the amount of solution.
Many ways of expressing concentration:
% by weight (% w/w)
% by volume (% v/v)
parts per million (ppm) or parts per billion (ppb) for very low concentrations
molality (m)
Molarity (M)

6. Concentrated vs. Dilute
The words “concentrated” and “dilute” are opposites.
EX: The dark tea is more concentrated than the light tea.
EX: The light tea is more dilute than the dark tea.

7. Concentrated vs. Dilute
Concentrated solution
Dilute solution
= solute particles

8. Percent by Weight % by weight (% w/w)
What is the % w/w of a solution if 3.00 grams of NaCl are dissolved in g of water?
mass of solute = 3.00 g
mass of solution = 3.00 g g = g
(3.00 g / g) x 100% = 15.0% w/w

9. Percent by Volume % by volume (% v/v)
What is the % v/v of a solution if 20.0 mL of alcohol are dissolved in 50.0 mL of solution?
volume of solute = 20.0 mL
volume of solution = 50.0 mL
(20.0 mL / 50.0 mL) x 100% = 40.0%

10. Molarity Molarity (M) UNITS: mol/L or Molar (M)
Example: mol/L = M

11. Molarity
What is the Molar concentration of a sol’n if 20.0 grams of KNO3 (MM = g/mol) is dissolved in enough water to make 800. mL?
Convert g of KNO3 to mol of KNO3
Convert mL to L

12. Molarity
What is the Molar concentration of a sol’n if mol KNO3 is dissolved in enough water to make L?

13. Molarity
What is the Molar concentration of a sol’n if 10.5 grams of glucose (MM = g/mol) is dissolved in enough water to make 20.0 mL of sol’n?
Convert g of glucose to mol of glucose.
Convert mL to L.

14. Molarity
What is the Molar concentration of a sol’n if mol of glucose is dissolved in enough water to make L of sol’n?

15. Calculating Grams
How many grams of KI (MM = g/mol) are needed to prepare 25.0 mL of a M solution?
Convert mL to L.
Solve for moles.
moles of KI = M x L = mol KI

16. Calculating Grams
How many grams of KI (MM = g/mol) are needed to prepare 25.0 mL of a M solution?
Convert mol KI to grams.

17. Calculating Grams
How many grams of HNO3 (MM = g/mol) are present in 50.0 mL of a 1.50 M sol’n?
Convert mL to L.
50.0 mL = L
Solve for moles:
moles = (1.50 M)( L) = mol HNO3
Convert mol HNO3 to grams:
mol HNO3 = 4.73 g HNO3

18. Dilution Dilute (verb) - to add solvent to a solution.
Decreases sol'n concentration.
M1V1 = M2V2
M1 = initial conc.
V1 = initial volume
M2 = final conc.
V2 = final volume
Assumes no solute is added.

19. Dilution Stock Solution Usable Solution
Impractically
High Concentration
Usable Solution
Add H2O
Question for Consideration: Why do you think chemical supply companies typically sell acids (and other solutions) in extremely high concentrations when it would be safer to ship more dilute solutions?

20. Dilution
To what volume should 40.0 mL of 18 M H2SO4 be diluted if a concentration of 3.0 M is desired?
What do we want to know? V2
What do we already know?
M1 = 18 M
V1 = 40.0 mL
M2 = 3.0 M
(18 M)(40.0 mL) = (3.0 M)V2
720 M*mL = (3.0 M)V2
V2 = 240 mL

21. Dilution
You are asked to prepare 500. mL of M HCl, starting with a 12.0 Molar stock sol'n. How much stock should you use?
What do we want to know? V1
What do we already know?
M1 = 12.0 M
M2 = M
V2 = 500. mL
(12.0 M) V1 = (0.250 M)(500. mL)‏
(12.0 M) V1 = 125 M*mL
V1 = 10.4 mL

22. Dilution
To how much water should you add 20.0 mL of 5.00 M HNO3 to dilute it to 1.00 M?
What do we want to know?
How much water to add. (V2 - V1)‏
What do we already know?
M1 = 5.00 M
V1 = 20.0 mL
M2 = 1.00 M
(5.00 M)(20.0 mL) = (1.00 M) V2
100. M*mL = (1.00 M) V2
V2 = 100. mL
Water added = 100. mL mL = 80. mL

23. Colligative Properties
Colligative properties are properties of solutions that are affected by the number of particles but not the identity of the solute

24. Boiling Point Elevation: A Colligative Property
Boiling point elevation is the temperature difference between a solution and pure solvent
The value of the boiling point elevation is directly proportional to molality, meaning the greater the number of solute particles, the greater the elevation

25. Freezing Point Depression: A Colligative Property
Freezing point depression is the difference in temperature between a solution and a pure solvent
The value of freezing point depression is directly proportional to molality, meaning the greater the number of solute particles