Solutions Chemistry B: Module 6

Solutions homogeneous mixture Parts Example: Solute – substance that dissolves Solvent – dissolving medium Example: Sugar and CO2 are solutes in water for most soft drinks What other solutes are in your favorite soft-drink?

Types of Solutions Depends on the state (or phase) of the solvent~ Gas – ex. Air, Nitrogen gas is the solvent Liquid – most common type; water is the most common solvent; ex. Sugar water, water is the solvent Solid –Nitrinol is titanium dissolved in nickel, used to make braces

Important Vocabulary Soluble – substance dissolves in solvent; ex. Sugar is soluble in water Insoluble – substance does not dissolve in solvent; ex. Sand is insoluble in water Immiscible – 2 substances that do not mix; ex. Oil and vinegar are immiscible Miscible – 2 liquids that are soluble in each other

Solvation – process of surrounding solute particles with solvent particles to form a solution Hydration – solvation in water “like dissolves like” – look at bonding and polarity of particles and the intermolecular forces between particles water molecules are dipoles; the oxygen end is a little bit negative and the hydrogen end is a little bit positive.

Solvation of ionic compounds water molecules collide with crystals the attraction between water dipoles and ions is stronger than the attraction between the ions this “pulls” the crystal apart Watch this animation

Solvation of Molecular Compounds sucrose, C12H22O11, is polar, the O-H bonds allow for H-bonding with water; oil also has O-H bonds but is nonpolar and therefore insoluble in water Heat of solvation – overall energy change that occurs during solution formation

Rate of Solvation increase collisions between solute and solvent by: agitating mixture, which increases surface area of solute increase temperature of solvent Increase the surface area by crushing the solute. HEAT IT! CRUSH IT! STIR IT!

Solubility Solubility – the maximum amount of solute that will dissolve in a given amount of solvent at a given temp and pressure; expressed as grams of solute per 100 g of solvent A solution that contains the maximum amount of dissolved solute for a given amount of solvent at a specific temp and pressure is saturated. A solution that contains less dissolved solute for a given temp and pressure than a saturated solution is unsaturated. A solution which contains more dissolved solute than a saturated solution at the same temp is supersaturated.

Solubility Diagrams Amount of water is 100g Dissolves better in Cold water=exothermic-feel HOT All gases are exothermic Represents saturated solutions at the given temperature Lines curving up are ENDOTHERMIC

Solubility Diagrams, cont using KNO3 as an example Any point on the line is SATURATED Any point below the line is UNSATURATED Solute that is dissolved above the line is SUPERSATURATED If you have a point above the line not dissolved that’s the excess sitting on the bottom of a saturated solution Take the QUIZ

Effect of Temperature on Solubility Solids – solubility increases as temperature increases Gases, Acids, and Bases – solubility decreases as temperature increases

Effect of Pressure on Solubility Only for gaseous solutions Solubility increases as external pressure increases.

Energy Terms~must know these! exothermic – a system that gives off energy, feels warm (gas, acid, base) + water  solution + heat endothermic – a system that absorbs energy, feels cool solid + water + heat  solution

Math of Solutions Easy formula Molarity-mole of solute in one liter of solution The greater the value the greater the concentration of solute Easy formula

Molality Molality=moles of solute per kg of solvent

Dilution Problems Use the following formula to determine the amount before or after adding solvent:

Bonus problem! Bonus Problem (+10 points) Show all work and turn in on a separate sheet of paper! If 10.4 grams of solute in 164 g of phenol lowers the solution’s freezing point to 36.3 °C from the solvent’s freezing point of 40.90 °C, what is the molar mass of the solute. (Kf of phenol = 7.40 FP of phenol = 40.90 °C)