CHEM 100

1
CHEM 100 Chemistry and Society Winter Quarter
2008 SCCC Lecture 38
In all the hurry to revise dont forget to do a
good job on lab reports.
2
What is a solvent? What is the solvent used in
most solutions?
A solvent is a liquid that dissolves a chemical
compound and is the major part of a solution. The
solvent used in most solutions is water.
3
How could you determine if a solution is
saturated or not?
You could tell if a solution is saturated or not
by attempting to dissolve more solute. If the
extra solute will not dissolve the solution is
saturated.
4
What is the role of spectator ions in a
precipitation reaction
Spectator ions undergo no chemical change during
a precipitation reaction. They are important
though as they balance the charge of the ions
being precipitated. A precipitation reaction
cannot occur without spectator ions as the charge
of the system would not balance.
5
What three things can be done to increase the
rate of at which a substance is dissolved?

• Three things that can be done to increase the
  rate at which a substance dissolves are
• increasing the surface area of the solute
• stirring
• heating the solution

6
Are weak acids inherently safer than strong
acids
No. The strength of an acid plays no role in
determining its concentration which is a major
factor in how harmful an acid is. Additionally
weak acids maybe very toxic even at low
concentrations (HF). We need to consider multiple
factors to determine the safety of any compound.
7
Name two types of reactions acids may undergo
Acids may undergo neutralization reactions when
they react with a base. Acids may undergo
oxidation-reduction reactions when they react
with a metal.
8
What could be done experimentally to determine
whether a solution contains a buffer
Buffers resist changes in pH when small amounts
of acid or base are added to them. To determine
if a solution contains a buffer we could add
small amounts of acid and base and measure how
the pH changes. We could compare this to what
happens when we add the same amounts of acid and
base to pure water. If the pH of our sample
remains relatively stable compared to water then
it probably contains a buffer.
9

• Identify each of the following as either an
  electrolyte or non-electrolyte
• NH4C2H3O2
• CH3OH
• HCl
• CO2

1. electrolyte
2. non-electrolyte
3. electrolyte
4. non-electrolyte

10
What type of interaction forces may exist in a
polar solvent?
Several interaction forces may exist in a polar
solvent. This include Van Der Waals or dispersion
forces, dipole-dipole forces, dipole-induced
dipole forces and depending on the composition of
the solvent H bonding.
11

• Place the following in order of their decreasing
  vapor pressure of water
• 0.1 M (NH4)2SO4
• 0.2 M CuSO4
• 0.15 M KI

(c) (a) lt (b)
12
What is diffusion?
Diffusion is the process in which solute
particles move by purely random motion from a
region of high concentration to region of lower
concentration within a solution.
13
What is osmosis?
Osmosis is the movement of solvent molecules
across a semi-permeable membrane. The solvent
moves from a region of low solute concentration
to a region of high solute concentration.
14
What is osmotic pressure?
The osmotic pressure of a solution is the
pressure required to prevent a net change in
solvent volume across a semi-permeable membrane.
15
What is meant when a system is said to be at
equilibrium
When the rate of two oppossing processes is equal
so that there is no change in system the system
is said to be at equilibrium.
16
What is the vapor pressure of a liquid?
The vapor pressure of a liquid is the pressure is
the pressure exerted by the vapor molecules.