Can be solid, liquid, or gas. Solutions Solution = homogeneous mixture Solute – subs. that is dissolved. Solvent – subs. that does the dissolving “Universal solvent” = water Can dissolve many (but not all) solutes. Solutions can also be gaseous, like the air you breathe, or even solid like brass. Can be solid, liquid, or gas.

Dissolving A solute dissolves into a solvent, normally water. In order for a solution to form, the attractions that hold the solute together and the solvent together must be overcome. “Like dissolves like” a substance with a certain polarity can only dissolve another substance if it exhibits that same polarity Remember, polar bonds share elect

Particles in solution Solute particles are separated from each other and are surrounded by solvent particles. Water is polar and easily dissolves ionic compounds (NaCl) Water can also dissolve many “nonpolar” particles because these particles may have a slight polar side of the molecule which allows the polar water to be attracted to these surfaces. Oil is nonpolar and can only be dissolved by other nonpolar substances like Ethanol or acetone. Because of its polarity, water is the “universal solvent” 3

3 ways to dissolve: 1. Dissociation of Ionic compounds An ionic compound separates into ions as it dissolves Example – NaCl in water This is a PHYSICAL change!

3 ways to dissolve: 2. Dispersion of molecular compounds Breaking into small pieces Example – sugar dissolving in water Both are polar molecules so they attract one another This is a PHYSICAL change!!

3 ways to dissolve: 3. Ionization of molecular compounds When neutral molecules gain or lose electrons Example – hydrogen chloride gas and water This is a CHEMICAL change! H2O + HCl  H3O+ + Cl- Notice that there are NO ions in the reactants, but that IONS are formed in the products.

Factors Affecting Rates of Dissolving Surface area The greater the surface area of the solute, the greater the collisions between solute and solvent molecules. Stirring Allows for more collisions because it moves dissolved particles away from surface of the solid. Temperature Allows for more collisions because you speed up the molecules! CHANGE THE CONCENTRATION

Effects of Solutes on the Solvent: Increased concentrations of solute in a solution will lower the freezing point and increase the boiling point of the pure solvent i. Salt spread over icy roads to melt the ice and turn it into water. ii. Salt placed into cooking water will increase the temperature of the water before it starts to boil, i.e. decreasing cooking time of pasta as it cooks in hotter water.

Concentration – amount of solute present Concentrated – strong solution “more” solute present Dilute – weak solution “less” solute present (“watered down”)

Soluble vs. Insoluble Soluble Insoluble A substance is said to be soluble in a substance, when it will dissolve in that substance. A substance is said to be insoluble in a substance, when it will not dissolve in that substance. Some substances are soluble in one solvent, but insoluble in another solvent.

Solubility Amount of solute that can be completely dissolved in a given amount of solvent at a given temp. Usually expressed in grams of solute per 100 grams of solvent. Solubility Curve—Curve showing how temperature affects the solubility of a substance.

How many grams of KNO3 will dissolve in 100 g of water at 60o C?

At what temperature will approximately 95 g of NaNO3 dissolve in 100 g of water? 30 oC

At what temperature will the same amount of KNO3 and NaNO3 dissolve in 100 g of water? ~ 68 oC

Levels of Saturation Unsaturated solution—solution “could” dissolve more solute. Point Below Line Saturated solution—Solution has dissolved all the solute possible. Point ON THE LINE Supersaturated solution—Solution has dissolved all solute possible, but more solute is added anyway. Point is ABOVE the Line Supersaturated solutions often crystalize once the solution has cooled down. Ex: “Hot ice” or Rock candy

Differing Degrees of Saturation = solute particles (not to scale) Supersaturated Unsaturated Saturated

A Theater Analogy A theater is designed to hold a certain number of people. This theater has many empty seats. It is similar to an unsaturated solution because it does not contain the maximum number of patrons.

A Theater Analogy This theater represents a saturated solution. Every available seat is occupied by a patron. The theater holds the maximum number of people.

A Theater Analogy This theater represents a supersaturated solution. There are more people crammed into the theater than it was designed to hold. Supersaturated solutions are very unstable.

Example videos! https://www.youtube.com/watch?v=tqypbI72Id8 https://www.youtube.com/watch?v=d7Qge1QbcaE

Need more help? https://www.youtube.com/watch?v=7AZ2Z6_CQmA

Saturated: ~50 g dissolved at 80 oC. Which term would describe a solution of 90 g of KCl dissolved in 100 g of water at 80 oC? Unsaturated Saturated Supersaturated Saturated: ~50 g dissolved at 80 oC.

Suppose 90 g of KI are placed in 100 g of water at 10 oC Suppose 90 g of KI are placed in 100 g of water at 10 oC. What type of solution would you have? Unsaturated Saturated Supersaturated Could dissolve about 135 g.

Properties of a Solution Properties of sol’n differ from properties of solute and solvent. conductivity – ionic solns conduct electricity. NaCl(aq) Salt dissolved in water freezing point – solns have lower freezing pt than pure solvent. Example: Salt on icy road. boiling point – solns have higher boiling pt than pure solvent. Example: Coolant in car radiators.

Factors Affecting Solubility Polar and nonpolar solvents (like dissolves like, so polar and nonpolar don’t usually mix) Temperature Solubility increases as temperature increases (when solids dissolve in liquids). Note that gases usually become less soluble as the temperature of the solvent increases. Pressure Increasing the pressure of a gas increases its solubility in a liquid.