1. Solutions

2. Solutions
What is a Solution? (5-1)

3. What is a solution?
Definition: When a substance dissolves, it goes into solution. It seems to disappear.
Definition: A solution is a mixture in which the molecules or ions of one substance mix evenly with the particles of another substance.
Example: When salt is mixed with water, it dissolves and seems to disappear. Actually, the sodium and chlorine ions mix evenly with the H2O molecules.

4. What is a solution? There are three different types of solutions…
Liquid solution
Formed when solids, liquids, or gases dissolve in liquids
Gaseous solution
Formed when solids, liquids, or gases dissolve in gases
Solid solution
Formed when solids, liquids, or gases dissolve in solids

5. What is a solution? TYPES OF SOLUTIONS Substance Dissolved in Examples
Liquid
Antifreeze in water
Gas
Water droplets in air (fog & clouds)
Solid
Sulfur in rubber
CO2 in water (club soda)
O2, Argon, and other gases in N2 (air)
Hydrogen in palladium
Salt in water (the oceans)
Iodine mist in air
Zinc in copper (brass)

6. What is a Solution? Which of the following mixtures are solutions?
Sugar & water
Sea water
Sand & water
Soda
Salt & pepper
Air
Brass
Mud
Cereal & milk

7. What are the parts of a solution? (5-2)
Solutions
What are the parts of a solution? (5-2)

8. What are the parts of a solution?
All solutions are made when one substance dissolves in another substance.
Thus there are two key ingredients to every solution:
Definition: The solute is the substance in the solution that dissolves.
Definition: The solvent is the substance in the solution in which a solute dissolves.

9. What are the parts of a solution?
Identify the solute and the solvent for each of the following solutions.
Solution
Solute
Solvent
Soda
Ocean water
Fog

10. What are the parts of a solution?
Definition: Some substances are more easily dissolved than other substances, thus they are more soluble.
Definition: The solubility of a substance is the maximum mass of that substance that will dissolve in 100 grams of solvent at a given temperature.
Example: Approx. 33 g of NaCl will dissolve in 100 g of H2O at 20oC. If you add any more NaCl to the solution, it won’t dissolve.

11. What are the parts of a solution?
The following graph shows the solubility of a number of different solutes when water is the solvent.
Note how the solubility of each solute changes as a function of the solvent’s temperature (the temperature of the water in this case).

12. What are the parts of a solution?
Note that for substances like sodium chloride (NaCl) and potassium nitrate (KNO3), that more solute can be dissolved as the temperature of the solvent (H2O in this case) increases. Thus their solubility increases!
For other substances like ammonia (NH3), more solute can be dissolved as the temperature of the solvent (again, H2O in this case) decreases. Thus their solubility decreases!

13. What are the parts of a solution?
Definition: A substance that is not able to dissolve in a given solvent (e.g. water), is said to be insoluble in that solvent.
Some solutes don’t dissolve as well as others, therefore they change the color of the solvent: for example, instant coffee in hot water.

14. Why is water a good solvent? (5-3)
Solutions
Why is water a good solvent? (5-3)

15. Why is water a good solvent?
Water is sometimes referred to as the “universal solvent.” Many substances dissolve in water!
Water is a particularly good solvent b/c its molecules are polar, meaning one side has a positive electric charge, and the other a negative electric charge.

16. Why is water a good solvent?
Water is called a polar solvent.
Polar solvents will dissolve ionic compounds, and compounds made up of other polar molecules.
For example: Oils and fats are composed of nonpolar molecules, therefore do not dissolve in water.

17. How can you change the rate at which substances dissolve? (5-4)
Solutions
How can you change the rate at which substances dissolve? (5-4)

18. Rate at which substances dissolve
There are several factors that affect the rate at which substances dissolve.
Stirring
Stirring & blending helps mix the solute evenly more quickly
Temperature
Solid solutes dissolve faster in liquid solvents as the temperature increases.
Gaseous solutes dissolve faster in liquid solvents as the temperature decreases.

19. Rate at which substances dissolve
There are several factors that affect the rate at which substances dissolve (cont’d).
Surface area
The smaller the size of the solute particle, the faster it dissolves.
Crushing, grinding, chopping, will all reduce the solute particle size.
Pressure
The higher the pressure, the more gas solute can dissolve.
Pressure has little to no effect on the rate at which solid or liquid solutes can dissolve.

20. Rate at which substances dissolve
There are several factors that affect the rate at which substances dissolve (cont’d).
Type of solvent
Some solvents dissolve certain solutes faster than others.
Polar solvents dissolve solutes with polar molecules and ionic compounds best.
Nonpolar solvents dissolve solvents with nonpolar molecules best.
In other words… “like dissolves like!”

21. How do solutes affect the freezing & boiling points? (5-6 & 5-7)
Solutions
How do solutes affect the freezing & boiling points? (5-6 & 5-7)

22. Freezing & Boiling Points
*Recall from earlier in the course... as heat energy is added to or removed from a substance, it can undergo a change of phase.
A physical change brought on by a change in the arrangement of the molecules.
See the phase-change diagram on the next slide. Note that the temperature doesn’t change while the substance changes phase.

23. Freezing & Boiling Points
Freezing Point

24. Freezing & Boiling Points
Freezing Point – The temperature at which a liquid changes to a solid (or vice versa).
Freezing Point Depression – Adding solute to a solvent lowers the freezing point of that solvent. The more solute, the lower the freezing point.

25. Freezing & Boiling Points
Ice Melting Solutes
Compound
Freezing Pt.
Advantages/Disad.
Rock Salt (NaCl)
-9oC
Abundunt & inexpensive BUT pollutes streams, lakes, & corrodes metal
Potassium Chloride (KCl)
-7oC
Less toxic than rock salt but too much can burn grass & plants
Calcium magnesium acetate (CMA)
Less toxic to plants than other salts & less corrosive to automobiles
Magnesium Cloride (MgCl2)
-15oC
Less toxic to plants & less damage ot concrete than rock salts
Calcium Chloride (CaCl2)
-32oC
Abundant & inexpensive BUT damages concrete, causes skin irritation

26. Freezing & Boiling Points
Boiling Point – The temperature at which a liquid changes to a gas (or vice versa).
Boiling Point Elevation– Adding solute to a solvent raises the boiling point of that solvent. The more solute, the higher the boiling point.
Example: Automobile antifreeze causes BOTH freezing point depression AND boiling point elevation!

27. Freezing & Boiling Points
Boiling Points of Different Solutions
Substance
Boiling Pt.
Distilled water
100oC
Sea water
103oC
Vinegar (acetic acid)
118oC
Ethyl alcohol
78.5oC
Acetone
56oC