Unit 6 Introduction to Chemistry Chapter 20 Mixtures and Solutions

20A – Heterogeneous Mixtures

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

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

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 And Take Notes… Section 20.7 Water – The Universal Solvent Section 20.8 The Solution Process Facet, page 468

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 freely 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

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 Read, page 473, Section 20.14