Solutions• Homogeneous mixtures containing

two or more substances.–Solvent- The substance that

dissolves

–Solute- The substance being dissolved

Solutions• May exist as a solid, liquid, or a

gas

• Water is the most prevalent solvent for solutions

Solubility• Soluble- Can be dissolved• Insoluble- Cannot be dissolved• Immiscible- When one liquid will

not dissolve in another• Miscible- When one liquid will

dissolve in another liquid

Solvation• The act of dissolving a solute• A solute will dissolve when the

attractive forces between the solute and the solvent are greater than the attractive forces holding the molecule together

Solvation

Water Molecules

Na Cl

Na Hydration Sphere

Cl Hydration Sphere

Ionic Solutions• As you recall H2O is a polar molecule

(charged on each end)• An ionic compound is composed of a

+ and – Ion. These ions are attracted to the oppositely charged end of the water molecule, pulling the ionic compound apart.

Ionic Solutions• The water surrounds the ions,

dissolving the compound.

Covalent Molecules• Water is also a good solvent for some

molecular compounds. • Sucrose is a polar molecular compound.

Water is also a polar molecule attracts the oppositely charged end of the sugar molecule.

• This pulls them apart causing solvation by water

Factors that Affect the Rate of Solvation

• Increasing the collisions of solvent and solute increases the solvation rate–Ways to increase collisions

• Increase the surface area of the solute

• Increase the temperature of the solution

• Agitate the mixture

Heat of Solution• The amount of energy required to

form a solution–It takes energy to overcome the

attractive forces that hold solute molecules together

Solubility• The maximum amount of solute

that can be dissolved at a given temperature and pressure

• Expressed in grams of solute per 100g of solvent

Types of Solutions• Saturated Solution- A solution that

contains the maximum amount of solute that it can hold.

• Unsaturated Solution- A solution that can dissolve more solute

• Supersaturated Solution- A solution that contains more solute than can normally be held in solution

Factors That Effect Solubility

• Temperature- As temperature increases –solubility increases for solid

substances

–Solubility decreases for gaseous substances

Factors the Effect Solubility

• Pressure- As pressure increases–Solubility for gases increases

Henry’s LawS1 = S2P1 P2At a given temperature the solubility

of a gas in a liquid is directly proportional to the pressure of a gas above the liquid

Practice Problem On Board

Concentration• A measure of how much solute is

dissolved in a specific amount of solvent–Concentrated- Lots of solute per

volume

–Dilute- Little solute per volume

Percent to Describe Concentration

• Percent by mass• Percent by mass= Mass of solute X 100

Mass of Solution

Percent by Volume• Percent by volume• Percent by volume = Volume of Solute x 100

Volume of Solution

Molarity• Molarity (M) = Moles of solute

Liters of Solution

Expressed in moles per liter

Assignment• P. 463 8-10

• P. 464 11-13

• P. 465 14-16

Preparing Molar Solutions

• How would you make a 1.5 molar solution of sucrose?

• 1.5 mol X 342g = 513g

• 1 L 1 mol 1 L

Preparing Molar Solutions

• How would you prepare 100ml of a 1.5 molar solution?

• 100ml X 1L X 513g = 51.3g

1000 ml 1 L

Diluting Solutions• M1V1=M2V2

• What volume (in ml) of a 12 M stock solution would be needed to make 50ml of a 2.5 M solution?

• (12M)(V1) = (2.5M)(.050L)

• 12V1= .125 V1= .0104L= 10.4ml

Molality• Molality= moles of solute

kg of solvent

Mole Fraction• XA = nA

nA + nB

What is the mole fraction of HCl in a solution that contains 21% HCl?

Mole Fraction• Assume there is 100g of solution

• This means that 21g of the solution is HCl and that 79g of the solution is water

• Convert both to moles

Mole Fraction• 21gHCl 1 mole = .583 moles

36g HCl

79gH2O 1 mole = 4.39 moles

18g H2O

Mole Fraction• XA = nA

nA + nB

XHCl = .583 = .117 HCl

.583 + 4.39

Colligative Properties• Properties that depend on the number

of particles in the solution but not the identity of the particles–Freezing point depression–Vapor pressure lowering–Boiling point elevation–Osmotic pressure

Electrolytes and Nonelectrolytes

• Electrolytes- Compounds that completely ionize in solution causing it to conduct electricity–Usually ionic compounds

• Nonelectrolytes- Compounds that do not ionize in solution and do not conduct electricity–Usually molecular compounds

Vapor Pressure Lowering• When a solute is dissolved in a liquid

the vapor pressure is lower above the solution than the vapor pressure of the pure solvent

• This is due to fewer solvent particles at the interface between the air and the surface of the solvent

• See diagram on p. 472

Boiling Point Elevation• The boiling point of a solvent increases

as solute is added to the solventTb = Kbm• Kb= molal boiling point constant• m = molality of the solutionTb =Value of boiling point elevation

Freezing Point Depression• As solute is added to a solvent the

freezing point is loweredTf = Kfm• Kf= molal freezing point constant• m = molality of the solutionTf =Value of freezing point depression

Osmosis and Osmotic Pressure

• Osmotic pressure increases with increase in amount of solvent

• Solute increases the number of solvent molecules that move across a membrane increasing the pressure

Assignment• P. 466 17-20

• P. 468 21-23

• P. 469 24-25

• P. 470 26-30

• P. 475 33-39