1. Solution Concentration
Section 15.2
Objectives:

2. Review
You have g of a bleach solution. The percent by mass of the solute NaClO is 3.62%. How many grams of NaClO are in the solution?
How many grams of solvent are in the solution?
What is the percent by volume of isopropyl alcohol in a solution that contains 24 mL of isopropyl alcohol in 1.1 L of water?

3. Expressing Concentration
% by mass
% by volume
Molarity
Molality
Mole fraction

4. Molarity (M)
Definition: the number of moles of solute dissolved in one liter of solution.
What would the units be?
Answer: moles/L, but we just use M, for “molar”
This is how most chemical solns are described.

5. Molarity, continued………
Example: What is the molarity of an aqueous soln containing 40.0 g of glucose in 1.5 L of soln?
What are the actual units for molarity?
So what 2 things do we need to have?
What 2 things are we GIVEN in this problem?
How do we get from what we HAVE to what we NEED?

6. Preparing Molar Solutions
What does “2M NaOH soln” mean?
Answer: 2 moles NaOH/1 L soln
So how would you prepare 100 mL of 2M NaOH?
Determine the number of moles of NaOH in 100 mL of solution.
Convert to grams of NaOH needed.
Add the NaOH to a flask, THEN add distilled water to the required volume.
WHY do we add solute FIRST?

7. Bellringer What does a 3.00M KI solution contain?
If M1V1 = M2V2, how much of the 3.00M KI soln would you need to make L of a 1.25M KI soln?
This is how you dilute a soln to make a soln of less concentration!
AND you have just done Practice Problem #21, p.468. 

8. Assignment – Part A
P.485: 80-82

9. Molality and Mole Fraction
What happens to the volume of a solution as the temperature increases?
So what would happen to its molarity?
Did the moles (or mass) of solute change?
Did the MASS of the solvent change?
So molarity changes, but masses do not.

10. Molality and Mole Fraction, continued………
Molality (m): the ratio(?) of the number of moles of solute dissolved in one kg of solvent
So m = ?????
Example 1 (#24, p.469): What is the molality of a soln containing 10.0 g Na2SO4 dissolved in g of water?
Example 2 (#25): What is the molality of a soln containing 30.0 g C10H8 dissolved in g of toluene?

11. Molality and Mole Fraction, continued………
Mole fraction (X): the ratio of the number of moles of solute in solution to the TOTAL number of moles of solute AND solvent.
XA represents the mole fraction of the solvent
XB represents the mole fraction of the solute
XA = ____nA____
(nA + nB)
So what does XB equal?????

12. Molality and Mole Fraction, continued………
Example 1 (#26, p.470): What is the mole fraction of NaOH in an aqueous soln that contains 22.8% NaOH by mass?
Example 2(#27): An aqueous soln of NaCl has a mole fraction of What is the mass of NaCl dissolved in mL of solution?

13. Assignment – Part B
P.485: 83-85
Study Guide for Content Mastery workbook: pp.86-88