SolutionsL

SolutionsMixture of substances (2+)State of matter depends on the solvent

Solute: substance that is dissolvedSolvent: substance that does the dissolving

Properties of solutionsHomogeneousCannot be filteredTransparentCan be separated by evaporating the solvent

SolubilitySoluble – if a substance can be dissolved in the

solvent AKA: Miscible

Insoluble – if a substance can not be dissolved in the solventAKA immiscible

Solubility -- How much solvent can be dissolved in a solute at a given temp and pressure

Like Dissolves Like!Polar compounds dissolve polar compounds

Water is the universal solvent because of its polarity

Non-polar compounds dissolve non-polar compoundsBenzene can dissolve plastic because both are

non-polar

Solvation

Rate of solubilitySince solubility occurs when molecules collide,

increasing the rate of collisions will increase how much quickly the solute dissolvesStirringIncreasing solute surface areaIncreasing temperature

Since the molecules of solvent have to move between the molecules of solute energy is absorbed (endothermic process)

Factors that effect solubilityTemperature

Effects solid solubility mainlyDirect relationship with solubility

PressureEffects gaseous solubility mainlySolubility increases as pressure around the

solute increases Soda is bottled at a higher pressure, when opened it

begins to effuse out.

Solubility curvesGraph assumes a 100g

sample of water, if you had 200g just double the values

Different phases dissolve differentlySolids

Higher solubility at higher temp.

(+) slopesGases

Higher solubility at lower temps (-) slopes

Solubility curves-think of it like a partySaturated – on the line

“We’re out of seats, no one can come in till someone leaves.”Unsaturated – below the line

Coach L’s usual party itinerary“We got room come on it!”

To calculate how much more can fit in find out how much under the line you are on the Y-axis

Supersaturated – above the line“I’ve hired a bouncer!”Excess is precipitate

Solid falls out of solution To calculate: find how much you are over on the Y-axis and subtract

till you get to the line

MolarityConcentration – how much stuff do you have

in a set spaceMolarity -- Concentration of molecules in a

solution

Molarity (M) = molsolute

Lsolution

You are usually given grams so you have to convert

You are usually given milliliters so you have to convert

Example:What is the molarity of a solution of 100L of

water and 36g of hydrochloric acid36g HCl X (1mol HCl/36g HCl) = 1mol HCl

1mol HCl/100L H2O = 0.01M HCl

Practice1. How many grams of CaCl2

would be dissolved in 1.0L of a 0.10M solution of CaCl2?

2. A Liter of 2M NaOH solution contains how many grams of NaOH?

3. How many grams of CaCl2 would need to dissolved in 500mL of water to make a 0.20M solution of CaCl2?

1. 11g CaCl2

2. 80g NaOH

3. 11g CaCl2

DilutionsSince the number of

Moles doesn’t change when we change the volume we can find the new concentration with the following formula

M1V1 = M2V2

Ex: what volume, in milliliters of 2.00M calcium chloride (CaCl2) stock solution would you use to make a 0.50L of 0.300M calcium chloride solution?

what volume, in milliliters of 2.00M calcium chloride (CaCl2) stock solution would you use to make a 0.50L of 0.300M calcium chloride solution?

M1V1 = M2V2

M1 = 2.00 M CaCl2

V1 = ? L of 2.00M CaCl2

M2 = 0.300M CaCl2

V2 = 0.50L of 0.3M CaCl2

2M (V1) = 0.3M (0.5L)

2M (V1) = 0.3M (0.5L)2M 2M

V1 = 0.075 L

V1 = 75mL

Practice1. What volume of a 3.0M KI solution

would you use to make 0.300L of a 1.25M KI solution?

2. How many milliliters of a 5.0M H2SO4 stock solution would you need to prepare 100mL of a 0.25M H2SO4

3. If you dilute 20.0mL of a 3.5M solution to make 100mL of solution, what is the molarity of the dilute solution?

1. 125mL

2. 5.0mL

3. 0.70M

Colligative Properties of solutionsPhysical properties of solutions that are effected by the number of

particles in solutions but NOT by the identity of dissolved particles in solution. Ionic compounds have a greater effect on colligative properties then

covalent compounds Dissociation factor(df)

How many ions does the compound form? For non-electrolytic compounds (covalent compounds) the df is

always one (1). For ionic compound the df is the number of ions that form that

compound.Effect:

Vapor pressure Boiling point Freezing point

Vapor pressurenumber of solvent particles exposed to

surface, less enter gas phaseLower vapor pressure

Boiling PointIncreases because fewer particles on the

surface are contributing to the vapor pressure (takes more energy to raise the vapor pressure)

Dependent on vapor pressureKb = difference in temp. of solution

and pure solvent

Freezing pointWhen kinetic energy can no longer overcome

attractionDecreases because solute particles get in the

way of attractive forces, cause the more energy to need to be lowered for phase change

Calculating the effect of solute on freezing points and boiling points

DT = m(df)KWhere DT = change in BP or FP (°C)

m = molarity or concentration of solution

df = dissociation factor K = constant for solvent (given)

What is the freezing point of a 0.40m solution of sucrose in ethanol, if ethanol’s normal freezing point is -114.1°C?DT = m(df)K m = 0.40mdf = 1K = 1.99 °C/m

DT = 0.40m (1) 1.99°C/m

DT = 0.796°CNew freezing piont = -114.1°C – 0.796°C =

-114.896°C