1. Solutions Part II: Units of Concentration (loosely from Jespersen Chap
Solutions Part II: Units of Concentration (loosely from Jespersen Chap. 13 Sec 5)
Dr. C. Yau
Fall 2014

2. Units of Concentration
Molarity (M)
Molality (m)
Mole fraction
& mole %
Mass %, ppt, ppm, ppb

3. Percent by Mass 1 million = 1,000,000 = 106
1 billion = 1,000,000,000 = 109

4. What does 15% w/w mean?
w/w means
15% w/w means
1 ppt means....?
15 ppb means....?

5. Example 13.2 p.598
Please don’t waste time copying the question. You can get it later from your textbook.
Seawater is typically 3.5% sea salt and has a density of about 1.03 g mL-1. How many grams of sea salt would be needed to prepare enough seawater solution to completely fill a 62.5 L aquarium? 5

6. Molality vs Molarity If we have a very dilute solution, such as
Know WHEN m is almost the same as M...under what conditions?
If we have a very dilute solution, such as
M which is
In such a solution, there is very little solute present, therefore 1 L soln = 1 L water.
Ans. m = M for very dilute solutions 6

7. Ex 13.3 p.599
An experiment calls for a m solution of sodium chloride in water. How many grams of NaCl would have to be dissolved in g of water to prepare a solution of this molality?

8. Interconversion of Units of Concentration
Example 13.4 p. 601
What is the molality of 10.0% w/w aq NaCl?

9. Example 13.5 p. 602
A certain supply of conc hydrochloric acid has a concentration of 36.0% HCl. The density of the solution is 1.19 g mL-1. Calculate the molar concentration of HCl.
Figure 12.4 Hydration of a polar molecule. A polar molecule of a molecular compound (such as the sugar glucose) can trade the forces of attraction it experiences for other molecules of its own kind for forces of attraction to molecules of water in an aqueous solution. Red areas indicate high electron density; blue areas have low electron density.

10. p.629 #13.48
What is the molality of NaCl in a solution that is M NaCl, with a density of
1.07 g mL-1?
Be sure to learn how to convert between different units of concentration.
Practice Exer 6-8 on p.600
Exer 9 & 10 on p.602
Exer 11 & 12 on p.603
Do as many as possible: p.629 #48-57.