SOLUTIONS Chapter 15

What are solutions?  Homogeneous mixtures containing two or more substances called the solute and the solvent  Solute- is the substance that dissolves  Solvent- is the dissolving medium  May exist as a solid, liquid or gas (usually are liquids)

 Soluble- A substance that dissolves in a solvent  Insoluble- A substance that does not dissolve in a solvent (ex. Sand is insoluble in water)  Immiscible- Two liquids that are insoluble in each other (ex. Oil and water)  Miscible- Two liquids that are soluble in each other (ex. Vinegar (water + acetic acid) )

Examples of Solutions

Solvation in Aqueous Solutions  Why are some substances soluble in one another whereas others are not?  Solvation- the process of surrounding solute particles with solvent particles to form a solution Solvation in water is called hydration “Likes dissolve likes” This phrase means that polar solvents dissolve polar solutes and nonpolar solvents dissolve nonpolar solutes.

Oil- Non PolarWater- Polar

Factors that affect the rate of solvation  Solvation occurs only when and where the solute and solvent particles come in contact with each other  Commons ways to increase the collisions  Agitating the mixture (stirring and shaking)  Increasing the surface area of the solute (breaking the solute into smaller pieces)  Increasing the temperature of the solvent (increases the kinetic energy)

Solubility  Solubility refers to the maximum amount of solute that will dissolve in a given amount of solvent at a specified temperature and pressure  Saturated solution- contains the maximum amount of dissolved solute for a given amount of solvent at a specific temperature and pressure  Unsaturated solution- contains less dissolved solute for a given temperature and pressure than a saturated solution  Supersaturated Solution- contains more dissolved solute than a saturated solution at the same temperature (and if you messed with the solution by shaking it or throwing in one more crystal, the whole thing would crystallize rapidly!)

Supersaturated Sodium Acetate Solution

Factors that Affect Solubility  Temperature  Many substances are more soluble at high temperatures than at low temperatures  Pressure  Solubility of a gas in a solvent increases as its external pressure (the pressure above the solution) increases

Henry’s Law  At a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid.  Formula:

Practice Problem  A gas has a solubility of 0.66 g/L at 10.0 atm of pressure. What is the pressure on a 1.0-L sample that contains 1.5 g of gas?

Solution Concentration  The concentration of a solution is a measure of how much is dissolved in a specific amount of solvent or solution  Qualitative Vocabulary  Dilute- contains a small amount of solute  Concentrated- contains a large amount of solute concentrated dilute

Expressing Concentration Concentration descriptionRatio Percent by mass Percent by volume Molarity Molality Mole Fraction

Calculating Percent my Mass  What is the percent my mass of NaHCO 3 in a solution containing 20 g NaHCO 3 dissolved in 600mL H 2 O?

Calculating Percent by Volume  What is the percent by volume of ethanol in a solution that contains 35 mL of ethanol dissolved in 115 mL of water?

Calculating Molarity  What is the molarity of an aqueous solution containing 40.0g of glucose (C 6 H 12 O 6 ) in 1.5 L of solution?

Preparing Molar Solutions How many grams of NaOH are in 250mL of a 3.0M NaOH solution?

Diluting Solutions M 1 xV 1 =M 2 xV 2 M 1 -- the initial concentration of the solution. V 1 -- the initial volume of the original solution that is going to be diluted with water. M 2 -- the final concentration of the solution after it’s diluted with water. V 2 -- the total volume of the final solution after it has been diluted with water.

Practice Problem  What volume of a 3.00M KI stock solution would you use to make L of a 1.25M KI solution?  If you dilute 20.0 mL of a 3.5M solution to make mL of solution, what is the molarity of the dilute solution?

Calculating Molality  What is the molality of a solution containing 30.0g of napthalene dissolved in 500.0g of toluene?

Calculating Mole Fraction  An aqueous solution of NaCl has a mole fraction of What is the mass of NaCl dissolved in 100.0mL of solution?

Colligative Properties of Solutions  Physical properties of solution that are affected the number of particles but not the identity of dissolved solute particles  Colligative Properties include:  Vapor Pressure Lowering  Boiling Point Elevation  Freezing Point Depression  Osmotic Pressure

Vapor Pressure Lowering  The greater the number of solute particles in a solvent, the lower the resulting vapor pressure

Boiling Point Elevation  The temperature difference between a solution’s boiling point and a pure solvent’s boiling point  Formula: ∆T b = K b m  K b is the molal boiling point elevation constant  m is the molality  The value of the boiling point elevation is directly proportional to the solution’s solute molality- the greater the number of solute particles in the solution, the greater the boiling point elevation

Freezing Point Depression  The temperature difference between a solution’s freezing point and a pure solvent’s freezing point  Formula: ∆T f = K f m  K f is the molal boiling point elevation constant  m is the molality

 Increasing Temperature 

Practice Problem  What are the boiling point and freezing point of a 0.40m solution of sucrose in ethanol?

Osmosis and Osmotic Pressure  Osmosis is the diffusion of solvent particles across a semipermeable membrane from an area of higher solvent concentration to an area of lower solvent concentration  Osmotic Pressure- the amount of additional pressure caused by the water molecules that moved into solution  Depends upon the number of solute particles in a given volume of solution