1. Chapter 7B- Concentration of Solutions

2. Concentration
Measure of the amount of solute that is dissolved in a given quantity of solvent
What is the solute? What is the solvent?
Qualitative descriptions
Dilute
Contains a small amount of solute
Concentrated
Contains a large amount of solute

3. How can Concentration be Expressed Quantitatively?
Formula is on Table T
Molarity (M) of a solution is the number of moles of solute in 1L of solution
The greater the molarity, the more concentrated the solution will be
8M of a solution is more concentrated than 1M of that solution
8molE/Liter vs. 1 mole/Liter

4. Example 1
What is the molarity of a 2.0L solution that was made up with 4.0 moles of NaCl?

5. Example 2
8 moles of HNO3 are dissolved in water to 10L. What is the molarity of the solution?

6. Example 3
How many moles of NaCl are needed to produce 3 Liters of a 2.0M solution?

7. Grams to Moles
Sometimes, they will give you the solute in grams instead of moles
We have done these problems before
First, convert grams to moles
Table T

8. Example 4
What is the molarity of a CaCl2 solution containing 330 grams of CaCl2 in 1L of solution?

9. Example 5
What is the molarity of a H2SO4 solution that contains 392 grams of H2SO4 in 2L of solution?

10. What if they give you the solution in milliliters instead of liters?
First, you have to convert mL to L
There are 1000ml in 1L
So, move the decimal point 3 places to the left
Or, divide by 1000
3000mL = ________ L
1500mL = ________ L

11. Example 6
What is the concentration of a solution which contains 2 moles of MgCl2 in 1000mL of solution?

12. How many moles of solute are contained in 300mL of 1M of solution?
Example 7
How many moles of solute are contained in 300mL of 1M of solution?

13. Percent by Mass and Percent by Volume
Ratio of one item to the entire product
Expressed in percent
Parts per Hundred
Cannot ever be more than 100%

14. Example 8
What is the percent by mass of sodium chloride if 2.5 grams of NaCl are added to 7.5 grams of water?

15. Example 9
What is the percent by volume of alcohol if 10.mL of ethanol is diluted with water to form a total volume of 100mL?

16. Parts per Million Very similar to percent composition
Only used in EXTREMELY SMALL measurements
Chlorine in a pool is 2g for every 1 million gallons
Dust particles and pollen in the air
The only difference is that you multiply your solute: solution ratio by 1,000,000 instead of 100.

17. Example 10
Texas had an allergy filled day. There were 4g of pollen in every 2000g of air. Express this in parts per million.

18. Example 11
Approximately g of carbon dioxide can be dissolved in 100mL of water. Express this in terms of parts per million.

19. Open your workbook to p. 128
24. 2 3 1 2 4 3 4 2 1

20. Colligative Properties
Freezing points and Boiling points change when nonvolatile solutes are added
Lowers freezing point
This is why you salt the sidewalks and streets after a snow storm or if it is below freezing outside.
Lowers the melting point so the ice will turn to water and evaporate away
Raising the boiling point
This is why you should boil the water before adding the salt when you make pasta
If you add the salt first, the water will have to heat for a longer time before it boils
The more concentrated (greater molarity) that the solute is, the greater the change

21. Example 12
Which solution has the highest boiling point? A- 1 mole of NaCl in 250g of water B- 1 mole of NaCl in 500g of water C- 1 mole of NaCl in 750g of water D- 1 mole of NaCl in 1000g of water

22. Example 13
Which solution would have the lowest freezing point? A- 0.5 mole of NaCl in 1000g of water B- 0.5 mole of NaCl in 500g of water C- 1 mole of NaCl in 1000g of water D- 1 mole of NaCl in 500g of water

23. Open your book to p (38-39, 41, 43) 1 3 2
43. 1

24. Vapor Pressure Molecules in a liquid are help together by weak forces
Dipole-dipole forces
Hydrogen bonds
When the particles have gained enough energy to escape, they enter the gas phase and become vapor
As temperature increases, particles gain more energy and escape more
The vapor particles exert pressure on the gaseous phase
Called Vapor Phase
Higher vapor pressure = weaker intermolecular forces
Graph of the boiling points of 4 liquids at different pressures
Table H

25. Example 14
What is the boiling point of propanone at an atmospheric pressure of 70kPa?

26. Example 15
In terms of intermolecular force, which liquid will evaporate more rapidly? Why?

27. Open your book to p.

28. Remember that it is on ALL of Chapter 7!!!
Study for your Test!!!
Remember that it is on ALL of Chapter 7!!!