What Are Solutions?

1
What Are Solutions?
2
What Are Solutions?

• Solution homogeneous mixture of 2 or more
  substances
• Solid, liquid, or gas
• Solvent dissolving medium
• Solute substance that dissolves
• When in solution, you cannot distinguish solvent
  and solute

3
What is a Solution?

• Soluble a substance that can dissolve in a
  given solvent
• Miscible two liquids that can dissolve in each
  other
• Example water and antifreeze
• Insoluble substance cannot dissolve
• Immiscible two liquids that cannot dissolve in
  each other
• Example oil water

4
Why Do Some Substances Dissolve and not Others?

• To dissolve, solute particles must dissociate
  from each other and mix with solvent particles
• Attractive forces between solute and solvent must
  be greater than attractive forces within the
  solute
• Process of surrounding solute particles with
  solvent particles is called SOLVATION
• In water, it is also called HYDRATION

5
Aqueous Solutions of Ionic Compounds

• Remember
• Water molecules are polar ( and ends)
• Water molecules are in constant motion
• When you put salt in water, water molecules
  collide with surface of crystal
• Charged ends of water attract ions of salt
• Dipole interaction (water/salt) is stronger than
  ions in crystal, so it pulls them away

6
Solvation
7
Aqueous Solutions of Molecular Compounds

• Water is also a good solvent for many molecular
  compounds (Example sugar)
• Sugar has many O-H bonds (polar)
• When water is added, the O-H bond becomes a site
  for hydrogen bonding with water
• Waters hydrogen bonds pulls the sugar molecules
  apart
• Oil is not a good solute because it has many C-H
  bonds (not polar) and few or no O-H (polar) bonds

8
Factors that Affect Solvation Rate

• Increase Solvation Rate (Dissolve Faster) by
• Agitation (stirring)
• Increase surface area (make particles smaller)
• Temperature (make it hotter)
• All these increase the number of collision
  between water and the solute

9
Heat of Solution

• During Solvation it takes energy to make the
  solute particles come apart.
• Solvent particles must also move apart
• This energy requirements is called Heat of
  Solution

10
Solubility

• Has Anyone ever made rock candy?
• How much water does it take to dissolve the sugar
  at room temperature?
• What happens when we raised the temperature?
• Only a limited amount of solute can dissolve in a
  given amount of solvent
• Every solute is unique for the solvent
• This is Solubility the amount of solute that
  can dissolve in a given amount of solvent at a
  specified temperature and pressure

11
Solubility Continued

• Solubility can also be understood at the particle
  level
• As particles collide, some particles are
  deposited back to the solute
• Some particles are removed from the solute.
• When the rate of deposit equals the rate of
  solvation, then the solution is SATURATED
• Saturated Solution no more solute can be
  dissolved in the solvent at this temperature and
  pressure
• Unsaturated Solution there is still room for
  more solute to be dissoved

12
Factors that Affect Solubility

• Most substances are MORE soluble at high
  temperature than at low
• If you dissolve a substance until saturated at
  high temperature and then reduce the temperature,
  the solution becomes supersaturated
• Supersaturated solutions are unstable
• A small change makes the solute reappear
• Rock candy worked that way. How?

13
Solubility
concentration
14
Solubility

• Solubility Curve
• shows the dependence of solubility on temperature

15
Solubility Chart
16
Solution Concentration

• Section 15.2

17
Expressing Concentration

• Concentration is a measure of how much solute is
  dissolved in a specific amount of solvent.
• Concentration can be qualitative or quantitative
• Qualitative strong, weak, etc.
• Quantitative percent by mass, percent by
  volume, molarity, molality

18
Molarity

• Molarity is the most common method of expressing
  concentration in Chemistry
• Molarity is moles of solute in 1 liter of
  solution.
• You make it by taking 1 mole of a solute and
  filling up with solvent to the 1 liter level.

19
Heterogeneous Mixtures

• Chapter 15.4

20
Types of Heterogeneous Mixtures

• Heterogeneous Mixtures
• Look like a solution, but are really mixtures
• Mixtures of substances that exist in 2 different
  phases
• 2 Types
• Suspensions
• Colloids
• Solutions
• Particles of solute are atomic sized compared to
  solvent

21
Suspensions

• Particle Size
• Suspended particles are large compared to solvent
  
• Larger than 1000 nm for solvated particles
• CAN be filtered
• When stirred, solid-like state begins to flow
  like a liquid
• Called Thixotropic
• Examples
• housepaint

22
Colloids

• Particle Size
• Particles of solute are intermediate sized
  (between atomic and large suspension sized)
  compared to solvent
• Between 1 nm and 1000 nm diameter
• Cannot be Separated by filtration or settling
• Example milk, butter, cheese,

23
Colloids

• Types of Colloids
• Solid Sol Solid in solid (gemstones)
• Sol Solid in Liquid (Blood, gelatin)
• Solid emulsion Liquid in solid (butter, cheese)
• Emulsion liquid/liquid (milk, mayonaise)
• Solid foam gas/solid (marshmallows, soap that
  floats)
• Foam gas/liquid (whipped cream, beaten egg
  whites)
• Aerosol solid/gas (smoke, dust in air)
• Aerosol liquid/gas (clouds, spray deodorant

24
Tyndall Effect

• Dilute Colloids sometimes appear as clear
  solutions (concentrated colloids do not)
• Because particles are too small to be seen with
  naked eye
• But dispersed colloid particles are large enough
  to scatter light
• Tyndall effect
• Solutions do not scatter light (particles are too
  small)

25
Tyndall Effect
Solution
Colloid
26
Electrolytes vs. Nonelectrolytes
The ammeter measures the flow of electrons
(current) through the circuit.

• If the ammeter measures a current, and the bulb
  
• glows, then the solution conducts.

• If the ammeter fails to measure a current, and
  the
• bulb does not glow, the solution is
  non-conducting.

27
Definition of Electrolytes and Nonelectrolytes
An electrolyte is

•   A substance whose aqueous solution conducts
• an electric current.

A nonelectrolyte is

•   A substance whose aqueous solution does not
• conduct an electric current.

Try to classify the following substances as
electrolytes or nonelectrolytes
28
Electrolytes?

• Pure water
• Tap water
• Sugar solution
• Sodium chloride solution
• Hydrochloric acid solution
• Lactic acid solution
• Ethyl alcohol solution
• Pure sodium chloride

29
ELECTROLYTES
NONELECTROLYTES

•   Tap water (weak)
•   NaCl solution
•   HCl solution
•   Lactate solution (weak)
•  
•  

•   Pure water
•   Sugar solution
•   Ethanol solution
•   Pure NaCl
•  

But why do some compounds conduct electricity in
solution while others do not?
Answers to Electrolytes