Unit 6 Introduction to Chemistry

1. Unit 6 Introduction to Chemistry Chapter 20 Mixtures and Solutions

2. 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

3. 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

4. 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

5. 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

6. 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

7. Summary of Mixtures in Phases

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. Read While Outlining… • Section 20.7 Water – The Universal Solvent • Section 20.8 The Solution Process • Facet, page 494

15. 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

16. 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

17. 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

18. 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

19. 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?

20. 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

21. 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