Chapter 15.2
Homogeneous Aqueous Systems
Chapter 15.3
Heterogeneous Aqueous Systems
Chapter 15.2
Homogeneous Aqueous Systems
Chapter 15.3
Heterogeneous Aqueous Systems
Learning Objectives
•
Understand the “s” words and how they are
different from each other (solution, solvent, solute)
•
Understand the process of solvation of ions
•
“Like dissolves like” and the difference between
polar and non-polar molecules when it comes to
solvation.
•
Electrolyte versus non-electrolyte
•
Solutions vs. colloids vs. suspensions
Solution (aq) – water that contains
dissolved substances
Solvent – The dissolving medium of the
solution (water in this chapter)
Solute – The solid that gets dissolved
Solvent plus solute = solution
How Does a Solution Form
Solvation
The ions are solvated
(surrounded by
solvent).
If the solvent is water,
the ions are hydrated.
When a substance becomes solvated
by water, we say it is soluble in water
• Chemists use the axiom “like dissolves like”:
Polar substances tend to dissolve in polar
solvents.
Nonpolar substances tend to dissolve in
nonpolar solvents.
Factors Affecting Solubility
• Vitamin A is soluble in nonpolar compounds (like
fats).
• Vitamin C is soluble in water.
Which vitamin
is watersoluble and
which is fatsoluble?
An electrolyte is a substance that, when dissolved in water,
results in a solution that can conduct electricity.
A nonelectrolyte is a substance that, when dissolved, results
in a solution that does not conduct electricity.
nonelectrolyte
weak electrolyte
strong electrolyte
4.1
All ionic compounds are electrolytes because
they break apart into ions when added to water
The next part of the textbook is about hydrates …
we will skip for the upcoming TWIZ
We did do a lab where we
heated a hydrate CuSO4 . 5H2O
and determined how much
water was released in moles.
The JELL-O mystery … what the heck is it?
It is a type of homogeneous aqueous system known as a
colloid.
JELL-O is a kind of strange substance which is
a colloid. JELL-O is made from water with
flavorings, sweetener, and gelatin mixed in.
Gelatin is made from a protein called collagen
which is the main protein in cartilage, the
flexible material that forms your outer ear and
nose. When JELL-O is added to hot water, the
long collagen molecules separate from each
other and mix throughout the water. But when
this mixture is cooled, the collagen molecules
link up with each other in a different way,
forming a 3-dimensional network. Water
molecules get trapped in the network and help
give JELL-O its more wiggly
characteristics. (adapted from ACS website)
More info about colloids
Colloids:
Suspensions of particles larger than
individual ions or molecules, but too small to
be settled out by gravity.
Particles are 1 nm – 1000 nm
Solutions
Example of a emulsion while
doing chemistry
Tyndall Effect
• Colloidal suspensions can
scatter rays of light
• This phenomenon is
known as the Tyndall effect
Suspension
• A mixture in which particles
are larger than in a colloid
(greater than 1000 nm)
– Particles are insoluble, so they DO NOT
dissolve in the liquid or gas.
– Particles can be separated using a filter.
• Examples:
• Salad dressing
• Medicines that say
“shake well before use”
Summary
Type of
Aqueous
System
Solution
Homogeneous
(Evenly dispersed)
Colloid
Homogeneous
(Evenly dispersed)
Suspension
Heterogeneous
(Unevenly dispersed)
Can you
Particle
see the
Size
solute?
Does it
scatter
light?
No
< 1 nm
No
No
Between
1 nm and
1000 nm
Yes
> 1000 nm
Depends on
size of particles
and how they
are dispersed
Yes