Solutions

From Chapters 12 and 13

Reading

• Chapter 12– Section 1 (pp. 363-366)– Section 4 (pp. 384-385)

• Chapter 13– all (pp.395-418)

Solutions

• homogenous mixture

• 2 parts1. solute - dissolved

2. solvent - does dissolving (greatest amount)

Solution examples

The Universal Solvent

Water H2O

• a part of almost every liquid on earth

• shape – bent

• polar

• high surface tension

• capillary action

• hydrogen bonding

Distinguish between…

soluble– if it will dissolve

miscible– liquids that will

dissolve in one another

insoluble– if it will NOTNOT

dissolve

immiscible– liquids that will

NOTNOT dissolve in one another

TYPES OF SOLUTIONS

1. solid solutions

• alloys – two or more solids evenly mixed– steel, brass

• amalgam – an alloy containing mercury– uses in dentistry, gold extraction,

industry

2. gas solutions

• gas dissolved in gas

– i.e. air– oxygen and other gases dissolved in

nitrogen

3. liquid solutions

• aqueous solutions– solvent is water

• tincture solutions– solvent is alcohol

• tincture of iodine

miscible/immiscible

Solvent Solute Example

Gas Gas air

Liquid Gas

Liquid

Solid

seltzer, soda

antifreeze, vinegar

salt water, sugar water

Solid Gas

Liquid

Solid

charcoal filter

dental filling

sterling silver

“like dissolves like”

• solvation – interaction of solute and solvent

• polar solvents dissolve polar and ionic substances

• non-polar solvents dissolve non-polar substances

hydrate

• when a compound contains water

i.e.– hydrated copper sulfate

– CuSO4 ∙ 5H2O

– copper sulfate pentahydrate

Suspensions

• particles are larger than in solutions

• particles evenly distributed by a mechanical means (i.e. shaking the contents)

• BUT the components will settle out.

Suspension Examples

• mud, muddy water

• paint

• flour suspended in water

• dust in air

• algae in water

Colloids• particles intermediate in size

between solutions and suspensions • microscopically evenly distributed

without settling out• ‘colloidal particles’ or colloids• ‘colloidal dispersion’

– A colloidal dispersion consists of colloids in a dispersing medium.

• Liquids, solids, and gases all may be mixed to form colloidal dispersions.

Colloid Examples• Aerosols: solid or liquid particles in a

gas.– Examples: Smoke is a solid in a gas. Fog

is a liquid in a gas.

• Sols: solid particles in a liquid– Example: Milk of Magnesia is a sol with

solid magnesium hydroxide in water.

• Emulsions: liquid particles in liquid.– Example: Mayonnaise is oil in water.

• Gels: liquids in solid.– Examples: gelatin is protein in water.

Quicksand is sand in water.

How to tell apart?• suspension particles will separate• colloids display Tyndall Effect• Tyndall effect - Light passing through

a colloidal dispersion will be reflected by the larger particles and the light beam will be visible

• solutions will not separate or scatter light

Electrolytes

• if something conducts electricity in solution – electrolyte

• if not – non-electrolyte

• if it conducts a little electricity – weak electrolyte

Factors Affecting Rate of Dissolving

• nature of the solute and solvent

Factors Affecting Rate of Dissolving

• temperature– higher temperature, more solute can

go into solution– gases are opposite

Factors Affecting Rate of Dissolving

• pressure– increased pressure increases gas

solubility– doesn’t affect liquids or solids

Factors Affecting Rate of Dissolving

• particle size– smaller particles dissolve faster– ‘increase surface area’

Factors Affecting Rate of Dissolving

• agitation– stirring increases rate of dissolution

Henry’s Law

• at a given temperature, the solubility of a gas in a liquid (S) is directly proportional to the pressure of a gas above the liquid (P)

S1 = S2

P1 P2

Solution concentration

• solubility– the amount of solute dissolved in a given

solvent at a specific temperature• i.e. solubility of sugar is 204 g per 100. g of

water at 20 C

• concentration– amount of solute in a given amount of

solvent or solution• measured in molarity (mol/L) or molality

(mol/kg)

Saturation• saturated

– maximum solubility– solution holds as much solution as

possibleunder given conditions (T&P)

• unsaturated– less than maximum

• supersaturated– greater than maximum– grows crystals– i.e. rock candy

Relative concentration

• concentrated – large amount of solute in small amount of solvent

• dilute – small amount of solute in large amount of solvent

• relative amounts, depends on what you compare it to

Molarity

molarity (M)

M = moles of solute

liters of solution

unit - mol/L

M1V1 = M2V2

Examples

• A saline solution contains 0.90g NaCl per 100 mL of solution. What is its molarity?

• A salt solution has a volume of 250 mL and contains 0.70 mol of NaCl, what is the molarity?

• How many moles of solute are present in 1.5 L of 0.2 M Na2SO4?

Examples

• What volume of MgSO4 is needed to prepare 100 mL of 0.4M solution from a 2.0 M solution?

• You need 250 mL of 0.20 M NaCl, but you only have a 1.0 M solution of sodium chloride, what do you do?

% solution

• % by volume– volume solute/volume solution x 100

• % by mass/volume– mass of solute/volume of solution x

100– g and mL

• ppm – number of grams per million grams

Examples

• What is the percent by volume of ethanol (C2H6O) in the final solution when 75 mL of ethanol is diluted to a volume of 250 mL with water?

• How many grams of glucose would you need to prepare 2.0L of 2.0% sucrose (m/v) solution?

Mixed Review

• A solution contains 2.7 g of CuSO4 in 75 mL of solution. What is the percent (m/v) of the solution?

• How many moles of solute are in 250 mL of 2.0 M CaCl2? How many grams of CaCl2 is this?

• How many grams of magnesium sulfate are required to make 250 mL of a 1.6% MgSO4 (m/v) solution

Mixed Review

• If 10 mL of acetic acid is diluted with 190 mL of water, what is the percent by volume of the acetic acid?

• An aqueous solution has a volume of 2.0 L and contains 36.0 g of glucose. If the molar mass of glucose is 180 g, what is the molarity of the solution?

Class work

• In grey books

– pg 390

– #26, 27, 28 (a-c), 30(a-b),

31 (a-b), 33

your books

- pg 942 #367-373

Homework

Molality

molality (m)

m = moles solute

kg solvent

unit: mol/kg

Examples

• How many grams of potassium iodide must be dissolved in 500. g of water to produce 0.060 molal KI solution?

• Calculate the molality of a solution prepared by dissolving 10.0 g of NaCl in 600.g of water.

mole fractionnumber of moles of one component divided by total number of moles of solution

• represented by Xx

Xsolute = moles of solute

moles of solution

Xsolvent = moles of solvent

moles of solution

Xsolute

+Xsolvent

1

Examples• Compute the mole fraction of each

component in a solution of 1.25 mol ethylene glycol (EG) and 4.00 mol water.

• What is the mole fraction of each component in a solution made by mixing 300. g of ethanol and 500. g of water?

• A solution is labeled 0.150 molal NaCl.What are the mole fractions of the solute and the solvent in this solution?

Class work

• In your blue books

• pg 421– 15b, 16, 17, 19c, 23, 24, 26, 28, 29, 32

• Homework: pg 941– 338-340, 350, 352, 365

Colligative Properties

• property that depends on concentration

• 4 types– vapor pressure reduction– boiling point elevation– freezing point depression– osmotic pressure

*note: colligative properties will be bonus questions on the test.

vapor pressure reduction

• vapor pressure over a solvent is reduced when a solute is dissolved in the solvent

boiling point elevation

• amount by which the boiling point is raised when a solute is in solution

• ∆Tb = Kbm(i)

• Kb – molal boiling point constant

• m – molality

• (i)Van’t Hoff factor

freezing point depression

• a dissolved solute lowers the freezing point

• ∆Tf = Kfm(i)

• Kf – freezing point depression constant

• m – molality

• (i)Van’t Hoff factor

osmotic pressure

• pressure required to prevent osmosis

• osmosis – net flow of solvent molecules from less concentrated solution to more concentrated solution