Chapter 23

SOLUTIONS

What is a solution?

• Solution—a mixture that has the same composition, color, density, and even taste throughout

• Ex: hummingbird food-has both sugar and red dye in the solution

• Solute—the substance being dissolved in a solution

• Solvent—the substance doing the dissolving in the solution

More on solutions

• Solutions can be composed of any combination of solids, liquids and gases

• Ex: air is a solution of 78% nitrogen, 20% oxygen and small amts of other gases such as argon, carbon dioxide and hydrogen

• Alloys-solid solutions– They are made by melting the metal solute

and solvent together

Dissolving

• Dissolving solids in liquids– Ex: hummingbird food, fruit drinks/sports

drinks– How do solids dissolve in water?

• Water molecules are constantly moving• Water molecules are also polar, and solute

molecules are polar as wellEx: pg. 709/Figure 3

How it Happens

• Water molecules cluster around solute molecules w/negative ends attracted to positive ends of the solute

• Water molecules pull the solute molecules into solution

• Water molecules and the solute molecules mix evenly, forming a solution

Dissolving Liquids and Gases

• When a gas dissolves in a liquid, particles of liquids and gases move much more freely than do particles of solids

• When gases dissolve in gases or when liquids dissolve in liquids, this movement spreads solutes evenly throughout the solvent

Dissolving Solids in Solids

• In order to mix to solids, ,

– Ex: two solid metals are first melted and then mixed together.

– In this liquid state, the metal atoms can spread out evenly and will remain mixed when cooled

Rate of Dissolving

• Stirring-a solutionspeeds up dissolving because it brings more fresh solvent into contact w/more solute

• Grinding lg. crystals (solids) into smaller ones speeds of dissolving also

• Temperature—increasing temperature of the solvent always speeds up the dissolving rate– Ex: hot chocolate

Gases in Solution

• When you shake an opened bottle of soda, it bubbles up and may squirt out

• Shaking or pouring a solution of a gas in a liquid causes gas to come out of solution

• If you want to dissolve more gas in a liquid, you can increase the pressure of that gas over the liquid– Ex: soft drinks (carbon dioxide pressure)

Temperature

• Another way to increase the amount of gas that dissolves in a liquid is to cool the liquid

• Ex: even more carbon dioxide will bubble out of a soft drink as it gets warmer

Section 2—Dissolving w/out Water

• **Water can’t dissolve some solutes because of its polarity

• **However, non-polar materials have no separated positive and negative areas.

• **Non-polar materials do not attract polar materials, which means they do not attract water

• SO:**Non-polar materials DO NOT dissolve in water

Non-polar Solutes

• Ex: vinegar and oil salad dressing has two layers—bottom layer is vinegar, and top layer is salad oil

• Equal distribution of electrons means the molecules of oil have no separate positive and negative areas, so they will not mix with water.

Versatile Alcohol

• Some substances form solutions w/polar and non-polar solutes

• They have molecules with both polar and non-polar ends

• The polar end dissolves polar substances, and vice versa.

• Ex: ethanol dissolves iodine and water

Useful Non-Polar Solvents

• Mineral Oil—used as a solvent to remove candle wax from glass, or metal or bubble gum from some surfaces

• Oil-based paints have materials dissolved in oils, so a non-polar solvent must be used to thin or remove them

• Dry cleaners use non-polar solvents when removing oily stains

Toxicity

• Although non-polar solvents have many uses, they have some drawbacks, too.____1. Many are flammable2. Some are toxic (skin/inhalation, etc)You must always be careful when handling these materials, and use a well ventilated area

How Soap Works

• The oils on human skin and hair keep them from drying out, but the oils can also attract and hold dirt

• Oily dirt is a nonpolar mixture, so e must wash with soap to get rid of dirt

• SOAP-has both non-polar and polar properties

• Soap is used to remove dirt from skin, hair, or fabric by attaching oily dirt to the hydrocarbon end and water to the ionic end

Polarity and Vitamins

• Having the right kinds and amounts of vitamins is important for your health

• B vitamins and vitamin C are polar compounds=they dissolve in water (water soluble)

• You must replace these vitamins by eating enough of the foods that contain them or by taking vitamin supplements

Fat-Soluble Vitamins

• Some vitamins such as vitamin A are non-polar and can dissolve in fat

• They do not wash away with water and are not easily eliminated by the body

• They can accumulate in tissues, which can become toxic

• Other ex: Vitamins D, E and K

Section 3—Solubility

• Solubility-the max amt. of a solute that can be dissolved in a given amt. of solvent at a given temp.

• The amount of a substance that can dissolve in a solvent depends on the nature of these substances– Explanation of how to determine solubility-

pg. 718

Concentration

• Ex: You add 1 tsp. of lemon juice to a glass of water

• Your friend adds 4 tsps. Of lemon juice to another glass the same size

• You could say your friend’s lemonade is concentrated, and your glass is dilute because your friend’s drink now has more lemon flavor than yours

More on Concentration/Dilution

• A concentrated solution is one in which a large amount of solute is dissolved in the solvent

• A dilute solution is one that has a small amount of solute in the solvent

• To measure concentration precisely it is sometimes given as a percent– (% fruit juice, etc.)

Types of Solutions

• Saturated solution-a solution that contains all the solute it can hold at a given temperature.

– (if heated, however, it could hold more)

– SO: as the temp of a liquid solvent increases, the amt of solid solute it can dissolve also increases

Types of Solutions

• Unsaturated solution—a solution that can dissolve more solute at a given temperature

• Each time a saturated solution is heated to a higher temp, it becomes unsaturated

Types of Solutions

• Supersaturated Solution-a solution that contains more solute than a saturated one at the same temperature

• Ex: if a seed crystal of sodium acetate is dropped into the supersaturated solution, excess sodium acetate crystallizes out

Solution Energy

• Some portable heat packs use crystallization from supersaturated solutions to produce heat

• After crystallization, the heat pack can be reused by heating it to again dissolve all the solute.

Section 4-Particles in Solution

• Ions-the charged particles in the fluids that are in and around all the cells in your body

• Electrolytes—the compounds that produce solutions of ions that conduct electricity in water– there are both strong (soldium chloride) and

weak electroylytes (acetic acid)– Nonelectrolytes—substances that form no

ions in water and cannot conduct electricity– Ex: ethyl alcohol and sucrose

How Ionic Solutions Form

• To form ions, the molecules must be broken apart in such a way that the atoms take on a charge

• Ionization—the process of forming ions so that molecules are broken apart and atoms take on a charge

• Dissociation—the process in which an ionic solid, such as sodium chloride, separates into its positive and negative ions– Ex: pg. 724

Effects of Solute Particles

• All solute particles-polar and nonpolar, electrolyte and nonelectrolyte, affect the physical properties of the solvent, such as its freezing point and its boiling point

• Ex: adding antifreeze to water in a car radiator lowers the freezing point of the radiator fluid– (sugar and salt would do the same thing)

• The effect that a solute has on the freezing pt or boiling pt of a solvent depends on the number of solute particles in solution, NOT on the chemical nature of the particles

• (it’s not a chemical reaction)

Lowering Freezing Point

• Adding antifreeze to a solvent lowers the freezing point of the solvent

• How much the freezing point goes down depends upon how many solute particles you add.

Raising Boiling Point

• Antifreeze also raises the boiling point of the water

• The amount the boiling point is raised depends upon the number solute molecules present

• Solute particles interfere w/evaporation of solvent particles

More on Raising the Boiling Point

• More energy is needed for the solvent particles to escape from the liquid surface, so the boiling point of the solution will be higher than the boiling point of solvent alone

Car Radiators

• When a car radiator contains water only, no antifreeze, the following occurs:

• Some of the molecules on the surface will vaporize and the number of molecules that do vaporize depends upon the temp of the solvent

• When the solvent heats up, the molecules move faster, and particles vaporize

• Finally when pressure of water vapor equals atmospheric pressure, water BOILS