Transcript Chapter 16 Solutions

Solutions
Chemistry Joke
What on earth
does this have to
do with
chemistry?
It’s a lit-moose test!
Solutions
 Homogeneous Mixtures
 Uniform throughout
 Composed of a solute and a solvent
 The solute is dissolved into the solvent
 The solute or the solvent can be a gas, a liquid,
or a solid.
 Air: gas / gas solution
 Salt water: solid / liquid solution
 Carbonated water: gas / liquid solution
 Steel: solid / solid solution
“Like Dissolves Like”
Polar solvents dissolve polar
solutes
Water is a polar molecule.
It has an uneven
distribution of charge.
Water will easily dissolve polar solutes
such NaCl.
“Like Dissolves Like”
 Nonpolar solvents dissolve
nonpolar solutes
Gasoline is a nonpolar molecule. It
has an even distribution of charge.
Gasoline is often used as a solvent
to clean nonpolar grease from
machine parts.
Making Solutions
 In order to dissolve, the solvent
molecules must come in contact with
the solute.
 Process is called solvation.
 3 Factors that affect the rate
 Stirring (agitation)
 Particle size (surface area)
 Temperature
Making Solutions
1. Stirring moves fresh solvent into contact
with the solute.
 It’s why we stir iced tea when we add
sugar.
2. Smaller pieces increase the amount of
surface area of the solute.
 Think of how fast a breath mint dissolves
when you chew it
Making Solutions
3. Higher temperature makes the molecules of
the solvent move around faster and contact
the solute harder and more often.
Slowest
Faster
Fastest
Making Solutions
So, the rate of solubility is affected by:
Stirring, Particle Size, & Temperature
What determines the amount of solute that
will dissolve?
Temperature & Pressure
Making Solutions
Temperature:
 Affects the solubility of solids, liquids, and
gases.
 For most solids and liquids, the solubility
increases with increasing temps.
 For most gases, the solubility decreases with
increasing temps.
 As carbonated drinks get warm, they get “flat”
Effect of Temperature

The mineral
deposits
around hot
springs result
from the
cooling of the
hot, saturated
solution of
minerals
emerging from
the spring.
- Page 474
Effect of Pressure
Pressure:
 Affects only the solubility of gases.
 Gas solubility increases as the
partial pressure of the gas above
the solution increases.
How Is Solubility Expressed?
Solubility
 Max amount of a substance that will
dissolve at a specific temp.
 Units are g solute/ 100 g solvent.
Saturated
 Contains the max amount of solute that
can dissolve
 Rate of particles dissolving equals rate of
particles crystalizing.
How Is Solubility Expressed?
Unsaturated
 Can still dissolve more solute
Supersaturated
 Holds more than it can theoretically
contain
How Is Solubility Expressed?
Electrolytes
 Compounds that conduct electricity in
aqueous solution or in a molten state
 All ionic compounds are electrolytes
 Some ionic compounds are strong
electrolytes; others are weak electrolytes.
 Strong electrolytes dissociate (break apart)
completely.
 Weak electrolytes only partially dissociate.
How Is Solubility Expressed?
 Most molecular compounds do not
conduct electricity.
 Called nonelectrolytes
 Sugar and rubbing alcohol are
nonelectrolytes
NaCl: Strong
Electrolyte
HgCl2: Weak
Electrolyte
Glucose:
NonElectrolyte
Colligative Properties

Properties that affect solutions.
 Depends only on the number of dissolved solute
particles—not on what kind of particle they are
Two important colligative properties are:
1) Boiling point elevation
As solute particles are added to a
solution, the boiling point rises.
2) Freezing point depression
As solute particles are added to a
solution, the freezing point lowers.
Ionic compounds work
best because they
dissociate in water into
more particles.
In water, NaCl becomes Na+ and Cl-.
Chemistry Joke
Q: Why did the white bear
dissolve in water?
A: Because it was polar!!