Unit 6 Introduction to Chemistry
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Transcript Unit 6 Introduction to Chemistry
Unit 6 Introduction to Chemistry
Chapter 20 Mixtures and
Solutions
20A – Heterogeneous Mixtures
Objectives:
Differentiate between homogeneous and heterogeneous
mixtures
Identify the continuous phase and the dispersed phase in a
mixture
Describe and give examples of the different kinds of
heterogeneous mixtures
Explain the differences between colloids and suspensions
Assignments: Outline and Section Review page 490
Introduction
All matter can be classified as either a pure substance or a mixture
Pure Substance
Element or compound
Mixture
Not chemically combined
Can be separated by physical means
Vary in their composition
Ratio of their components can very in proportion
Classification depends
On size of the particles
How evenly the particles are mixed
Homogeneous mixture
Solution
Particles are small and uniformly mixed
Heterogeneous mixture
Particles are large and not uniformly mixed
Classifying Mixtures by Phase
Heterogeneous mixtures contain two or more phases, or distinct parts
Continuous phase
One unbroken phase in which the other phases are mixed
Dispersed phases
The other phases
Gels
A two phased mixture
Consist of a solid dispersed in a liquid
Mostly liquid, but have some solid properties
Jello
Sols
Solid in liquid mixture that acts more like a liquid
Thick or viscous liquids
Paints and inks
Classifying Mixtures by Phase
Emulsions
Mixtures that contain two or more distinct liquid phases
They are immiscible
Cannot be blended into one another
Milk, mayonnaise, butter
Each dispersed phase will usually separate fro the continuous phase
over time to form a layer
Process can be slowed by homogenization, but not completely
stopped
Classifying Mixtures by Phase
Foams
Forms when a gas is whipped into a liquid so that it makes a mixture
of tiny bubbles within the liquid
Whipped cream, shaving cream
Aerosols
Solid particles or liquid drops that are dispersed in a gas
Natural and man made sources of aerosols fill the atmosphere
Dust, salt crystals, water droplets, smoke, fog
Heterogeneous Alloys
Mixing of metals to improve quality
Sterling silver, stainless steel
Summary of Mixtures in Phases
Classifying Mixtures by Particle Size
Colloidal Dispersions
Many heterogeneous mixtures often appear homogeneous until you
look at the microscopic level
If the particle size is between 1 nm and 1 um the mixture is a
colloidal dispersion
The dispersed particles are called colloids
Too small to settle out of the continuous phase by the force of
gravity alone
Particles are too small to scatter light
Read, page 489
Classifying Mixtures by Particle Size
Suspensions
Fluid mixtures
Dispersed particles are larger than 1 um in size
These particles will eventually settle out of the mixture under the
influence of gravity
Form a layer of sediment at the bottom of the fluid if left
undisturbed
The particles are large enough to scatter light
Tyndall Effect, will not be seen in true solutions
20B – Homogeneous Mixtures: Solutions
Objectives:
List the properties that characterize solutions and identify which ones are
shared with other mixtures
Identify the kinds of solutions possible
Describe the properties of water that make it a good solvent
Explain how solute particles dissolve
Differentiate between dissociation and ionization
Define solubility and explain what factors affect it
Identify two factors that can affect the solubilities of various substances
Compare unsaturated, saturated, and supersaturated solutions
Explain conditions that can affect the rate of solution
Assignments: Outline and Section Review page 500
Defining Solutions
Solutions
Homogeneous, or uniform, mixtures of pure substances that consist
of a single phase
In its simplest form it is one substance dissolved into another
The substance that is dissolved is called the solute
The substance that does the dissolving is called the solvent
Sometime that is hard to distinguish, especially if the substances are
both liquids
A more complete definition
The solute is the substance in a solution that is present in the
smaller amount, while the solvent is the substance present in the
larger amount
Properties of Solutions
Characteristics of True Solutions
Solutions are homogeneous
Solutes cannot be filtered out of a solution
Solutes do not settle out of a solution
True fluid solutions are transparent and do not display the Tyndall
effect
Characteristics of all mixtures
Components of a solution are not chemically combined
The compositions of solutions can vary
The main difference between solutions and other mixtures is particle
size
Types of Solutions
Solutions can be solids, liquids, or gases
Solutions are categorized by the solvent’s state of matter
Liquid Solutions
Solvent is a liquid
Solute can be a solid, liquid, or gas
Salt water
Vinegar
Carbonated beverages
Solid Solutions?
Read, page 492
Gaseous Solutions
Solvent and solute are both gases
Most common example is air
Read While Outlining…
Section 20.7 Water – The Universal Solvent
Section 20.8 The Solution Process
Facet, page 494
Solubility
A substance is considered to be soluble when it can be dissolved by a
solvent
Substances that dissolve in water are usually polar
Like dissolves like
Liquids that can feely mix in any proportion are said to be miscible
Solubility
The maximum amount of solute that will dissolve in a given amount
of solvent at a given temperature
Through water is often said to be the universal solvent some
substances do not dissolve in water and are said to be insoluble or if
a liquid, immiscible
Factors Affecting Solubility
Temperature
For a solid and a liquid solubility increases as temperature increases
For a gas solubility decreases as temperature increases
Pressure
Henry’s Law
The greater the pressure of a gas on a liquid, the greater the mass of the gas
that will remain dissolved at any given temperature
Think of a soda…
Saturation
Saturated
More solute is added than can be dissolved at a given temperature
Unsaturated
Less solute than their solubility at a given temperature
Supersaturated
More solute than a saturated solution at a given temperature
Unstable
Used to make crystals
Rate of Solution
How much solute dissolves is different than how fast it dissolves
Three factors that affect rate of solution
Stirring
Temperature
Surface area
20C – Solution Concentration
Objectives:
Define the terms concentration, concentrated, and dilute
Describe two ways to measure the concentration of a
solution
Define the mole and state its value
State and describe three colligative properties
Explain the processes of osmosis and reverse osmosis
Assignments: Outline and Section Review page 506
Concentration
Have you ever had sweet tea, that wasn’t sweet enough?
How about fruit punch that tasted more like water?
Concentration
The amount of solute in a certain amount of solvent
Do you want your solution to be concentrated or dilute?
Ways to Measure Concentration
Percentage by Mass
The mass of solute per 100 grams of solution
Molarity
Most accurate way to measure concentration
Moles/liter
Colligative Properties
Properties related to the number of solute particles in a solution and
not due to the properties of the solute itself
Freezing-Point Depression
Boiling-Point Depression
Osmotic Pressure
Let’s Read, page 501