1. Solutions
Concentration

2. Concentration The amount of solute in a solution.
Describing Concentration
% by mass - medicated creams
% by volume - rubbing alcohol
ppm, ppb - water contaminants
molarity - used by chemists
molality - used by chemists

3. Liters of total solution (solute + solvent)
Molarity
Liters of total solution (solute + solvent)

4. Molarity
What is the molarity of a solution with 25.0g of NaCl in 1.75 L?
25.0 g NaCl
1 mol NaCl
58.44 g
1.75 L
= M

5. Molarity
How many grams of NaCl are required to make 1 L of a M solution?
0.500 mol NaCl
58.44 g
1 L
1 mol
= 29.2 g to make 1 L

6. Molality
mass of solvent only
1 kg water = 1 L water

7. Molality
Find the molality of a solution containing 75 g of MgCl2 in 250 mL of water.
75 g MgCl2
1 mol MgCl2
95.21 g MgCl2
0.25 kg water
= 3.2m MgCl2

8. Molality
How many grams of NaCl are req’d to make a 1.54m solution using kg of water?
0.500 kg water
1.54 mol NaCl
1 kg water
58.44 g NaCl
1 mol NaCl
= 45.0 g NaCl

9. Dilution
Preparation of a desired solution by adding water to a concentrate.
Moles of solute remain the same.

10. Dilution
What volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution?
GIVEN:
M1 = 15.8M
V1 = ?
M2 = 6.0M
V2 = 250 mL
WORK:
M1 V1 = M2 V2
(15.8M) V1 = (6.0M)(250mL)
V1 = 95 mL of 15.8M HNO3

11. Preparing Solutions 1.54m NaCl in 0.500 kg of water
500 mL of 1.54M NaCl
mass 45.0 g of NaCl
add water until total volume is 500 mL
mass 45.0 g of NaCl
add kg of water
500 mL water
45.0 g NaCl
500 mL
mark
volumetric
flask

12. Preparing Solutions
Copyright © NT Curriculum Project, UW-Madison
(above: “Filling the volumetric flask”)

13. Preparing Solutions
Copyright © NT Curriculum Project, UW-Madison
(above: “Using your hand as a stopper”)

14. Preparing Solutions 250 mL of 6.0M HNO3 by dilution
measure 95 mL of 15.8M HNO3
95 mL of 15.8M HNO3
combine with water until total volume is 250 mL
250 mL mark
Safety: “Do as you oughtta, add the acid to the watta!”
water for safety