1. Unit 4: Solutions & Solubility
6.1/6.2 Defining and Explaining Solutions

2. Solutions: a definition
a type of mixture
mixtures can be separated by non-chemical means such as filtration, heating, or centrifugation
a homogeneous mixture
the mixture is the same all the way through
does not settle out if left to sit, whereas most heterogeneous mixtures do

3. Homogenous vs. Heterogeneous

4. The Parts of a Solution
Solute = a substance that is dissolved in a solvent (e.g. salt, NaCl, in saltwater)
Solvent = the medium in which a solute is dissolved; often the liquid component of a solution (e.g. water, in saltwater)
in a solution, there is more solvent than solute

5. Solutions

6. Classifying Solutions
Types of Solutions:
Electrical Conductivity
Electrolyte
Nonelectrolyte
The state of their solute and solvent
gas solute in gas solvent (eg. air)
Solid solute in liquid solvent (eg. saltwater)
pH (Acid, Base or Neither)
Acidic
Basic
Neutral

7. Conductivity
Electrolyte = a compound that, in an aqueous solution (water is the solvent), conducts electricity
Mostly ionic compounds
Nonelectrolyte = a compound that, in an aqueous solution, does not conduct electricity
Mostly molecular compounds

8. pH
Acid = a substance that, in aqueous solution, turns litmus paper red (pH is less than 7)
Base = a substance that in an aqueous solution, turns litmus paper blue (pH is greater than 7)
Neutral = a substance that, in aqueous solution, has no effect on either red or blue litmus paper; neither acidic nor basic (pH = 7)

9. Unit 4: Solutions & Solubility
6.2 Explaining Solutions

10. Explaining Solutions
Why do only some chemicals dissolve in water? Why are some chemicals mutually attracted to one another?
Recall:
Intermolecular Forces = an attraction between molecules

11. Polarity and Solubility
Polar substances dissolve in polar solvents
Polar solute molecules are surrounded and suspended in solution by polar solvent molecules (see handout)
Non-polar substances dissolve in non-polar solvents
In other words:
like-polarity substances dissolve in each other (“like dissolves like”)

12. Explaining Non-aqueous Mixtures
London Dispersion forces are weak intermolecular forces responsible for non- polar substances dissolving in non-polar solvents

13. Recall: Hydrogen Bonding
a relatively strong dipole-dipole force between a solute with N, O, or F lone pairs or with a H-N, H-O, or H-F bond and water
when multiple hydrogen bonds between solute and solvent is possible, we would expect an especially high solubility (see handout)

14. Hydrogen Bonds between water molecules

15. Ionic Compounds in Water
More ionic compounds dissolve in water than in any other known solvent…
Ionic compounds dissociate into individual aqueous ions (see handout)
Dissociation = the separation of ions that occurs when an ionic compound dissolves in water (see handout)

16. Ionic Compounds in Water

17. Ionic Compounds in Water

18. Predicting Solubility: Group Activity
Rank the molecular compounds from greatest to least solubility in water and explain your prediction.
Hint: examine the Lewis structures carefully and consider the type of intermolecular bond (LF, D-D or H-B) that it forms with water.
Also, consider the possibility of multiple hydrogen bonds.

19. Homework: Read pg. 268 - 279 Do #3, 5 on pg. 277