Unit 4: Solutions & Solubility
6.1/6.2 Defining and Explaining Solutions
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
Homogenous vs. Heterogeneous
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
Solutions
Classifying Solutions

Types of Solutions:

Electrical Conductivity

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The state of their solute and solvent

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
Electrolyte
Nonelectrolyte
gas solute in gas solvent (eg. air)
Solid solute in liquid solvent (eg. saltwater)
pH (Acid, Base or Neither)


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Acidic
Basic
Neutral
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
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)

Unit 4: Solutions & Solubility
6.2 Explaining Solutions
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
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”)
Explaining Non-aqueous Mixtures

London Dispersion forces are weak
intermolecular forces responsible for nonpolar substances dissolving in non-polar
solvents
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)
Hydrogen Bonds between water
molecules
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)
Ionic Compounds in Water
Ionic Compounds in Water
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.

Homework:
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Read pg. 268 - 279
Do #3, 5 on pg. 277
Do #7, 9 – 11 on pg. 279