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