I. The Nature of SolutionsI. The Nature of Solutions

(p. 401 - 410, 425 - 433)(p. 401 - 410, 425 - 433)

Classification of MatterClassification of MatterSolutions are homogeneous mixtures

SoluteSoluteA solute is the dissolved substance in a solution.

A solvent is the dissolving medium in a solution.

SolvenSolventt

Salt in salt water Sugar in soda drinks

Carbon dioxide in soda drinks

Water in salt water Water in soda

Dental filling

Solution = Solute + Solvent

• Solute - gets dissolved 

• Solvent - does the dissolving – Aqueous (water)

– Tincture (alcohol)

– Amalgam (mercury)

– Organic • Polar • Non-polar

Dental filling

Nightmare on White Street Chem Matters, December 1996

SolventsSolvents

Solvents at the hardware store

Suspensions and Suspensions and ColloidsColloids

Suspensions and colloids are NOT solutions. Suspensions: The particles are so large that they settle out of the solvent if not constantly stirred.

Colloids: The particle is intermediate in size between those of a suspension and those of a solution.

Types of Colloids Examples Dispersin

g Medium/ major comp

Dispersed Substance/Minor comp

Colloid Type

Fog, aerosol sprays Gas Liquid Aerosol

Smoke, airborne bacteria Gas Solid Aerosol

Whipped cream, soap suds

Liquid Gas Foam

Milk, mayonnaise Liquid Liquid Emulsion

Paint, clays, gelatin Liquid Solid Sol

Marshmallow, Styrofoam Solid Gas Solid foam

Butter, cheese Solid Liquid Solid emulsion

Ruby glass Solid Solid Solid sol

The Tyndall EffectThe Tyndall Effect

Colloids scatter light, making a beam visible. Solutions do not scatter light.

Which glass contains a colloid?

solutioncolloid

The ammeter measures the flow of electrons (current) through the circuit.

If the ammeter measures a current, and the bulb glows, then the solution conducts.

If the ammeter fails to measure a current, and the bulb does not glow, the solution is non-conducting.

Electrolytes vs. Electrolytes vs. NonelectrolytesNonelectrolytes

An electrolyte is:

  A substance whose aqueous solution conducts an electric current.

A nonelectrolyte is:

  A substance whose aqueous solution does not conduct an electric current.

Try to classify the following substances as electrolytes or nonelectrolytes…

Definition of Electrolytes and Definition of Electrolytes and NonelectrolytesNonelectrolytes

1.Pure water 2.Tap water 3.Sugar solution 4.Sodium chloride solution 5.Hydrochloric acid solution 6.Lactic acid solution 7.Ethyl alcohol solution 8.Pure sodium chloride

Electrolytes?Electrolytes?

ELECTROLYTES: NONELECTROLYTES:

  Tap water (weak)

  NaCl solution

  HCl solution

  Lactate solution (weak)

 

 

  Pure water

  Sugar solution

  Ethanol solution

  Pure NaCl

  But why do some compounds conduct electricity in solution while others do not…?

Answers to ElectrolytesAnswers to Electrolytes

B. Solvation

• Solvation – the process of dissolving

solute particles are separated and pulled into solution

solute particles are surrounded by solvent particles

Solvation

StrongElectrolyte

Non-Electrolyte

solute exists asions only

- +

salt

- +

sugar

solute exists asmolecules

only

- +

acetic acid

WeakElectrolyte

solute exists asions and

molecules DISSOCIATION IONIZATION

http://www.mhhe.com/physsci/chemistry/animations/chang_2e/molecular_view.swf

Solvation

NONPOLAR

NONPOLAR

POLAR

POLAR

“Like Dissolves Like”“Like Dissolves Like”

Solvation

• Soap/Detergent– polar “head” with long nonpolar “tail”– dissolves nonpolar grease in polar water

Solubility

• Solubility– maximum grams of solute that will dissolve in

100 g of solvent at a given temperature– varies with temp– based on a saturated soln

Factors Affecting SolubilityFactors Affecting Solubility The solubility of MOST solids The solubility of MOST solids

increases with temperature.increases with temperature. The rate at which solids dissolve The rate at which solids dissolve

increases with increasing surface increases with increasing surface area of the solid. area of the solid.

The solubility of gases decreases The solubility of gases decreases with increases in temperature. with increases in temperature.

The solubility of gases increases with The solubility of gases increases with the pressure above the solution.the pressure above the solution.

Therefore…Therefore…Solids tend to dissolve best when:

o Heated o Stirred o Ground into small particles

Liquids tend to dissolve best when:o The solution is cold

o Pressure is high

Saturation of SolutionsSaturation of Solutions A solution that contains the maximum A solution that contains the maximum

amount of solute that may be dissolved amount of solute that may be dissolved under existing conditions is under existing conditions is saturatedsaturated. .

A solution that contains less solute than A solution that contains less solute than a saturated solution under existing a saturated solution under existing conditions is conditions is unsaturatedunsaturated. .

A solution that contains more dissolved A solution that contains more dissolved solute than a saturated solution under solute than a saturated solution under the same conditions is the same conditions is supersaturatedsupersaturated..

Solubility

SATURATED SOLUTION

no more solute dissolves

UNSATURATED SOLUTIONmore solute dissolves

SUPERSATURATED SOLUTION

becomes unstable, crystals form

concentration

Solubility

• Solids are more soluble at...– high temperatures.

• Gases are more soluble at...– low temperatures &

– high pressures (Henry’s Law).

– EX: nitrogen narcosis, the “bends,” soda

Solubility

• Solubility Curve– shows the

dependence of solubility on temperature

Solubility ChartSolubility Chart

Calculations of Solution Calculations of Solution ConcentrationConcentration

ConcentrationConcentration - A measure of the amount of - A measure of the amount of

solute in a given amount of solvent or solutionsolute in a given amount of solvent or solution

Molarity - moles of solute divided by the volume of solution in liters

Parts per million – the ratio of parts (mass) of solute to one million parts (mass) of solution

Grams per liter - the mass of solute divided by the volume of solution, in liters

Percent composition - the ratio of one part of solute to one hundred parts of solution, expressed as a percent

A. Concentration• Describing Concentration

– % by mass - medicated creams (V/V, m/V, W/W)1. % V/V = 4.1 L / 55 L = 7.5% V/V2. % W/V = 16 g / 50 mL = 32% W/V3. % W/W = 1.7 g / 35.0 g = 4.9% W/W

– % by volume - rubbing alcohol

– ppm, ppb - water contaminants

8 ppm = 8 _ / 1 L, the units should be 1 million times smaller than 1L (or 1kg): 8ppm = 8 mg/L so the mass in 1 L is 8 mg.

– molarity - used by chemists

– molality - used by chemists

B. Molality

solvent ofkg

solute of moles(m)molality

mass of solvent only

1 kg water = 1 L water

kg 1

mol0.25 0.25m

2211 VMVM

C. Dilution

• Preparation of a desired solution by adding water to a concentrate.

• Moles of solute remain the same.

Concentrated vs. DiluteConcentrated vs. Dilute

D. Preparing Solutions

• 500 mL of 1.54M NaCl

500 mLwater

45.0 gNaCl

– mass 45.0 g of NaCl– add water until total

volume is 500 mL– mass 45.0 g of NaCl– add 0.500 kg of water

500 mLmark

500 mLvolumetric

flask

• 1.54m NaCl in 0.500 kg of water

D. Preparing Solutions

Copyright © 1995-1996 NT Curriculum Project, UW-Madison(above: “Using your hand as a stopper”)

D. Preparing Solutions

• 250 mL of 6.0M HNO3 by dilution– measure 95 mL

of 15.8M HNO3

95 mL of15.8M HNO3

water for

safety

250 mL mark

– combine with water until total volume is 250 mL

– Safety: “Do as you oughtta, add the acid to the watta!”

C. Calculations

• How many grams of solute are present in 1.5 L of 0.24 M Na2SO4?

V= 1.5 LM=0.24MM = mol of solute per liter of solution

WORK:

mol = mass ÷ molar mass

GIVEN:Mass = ?Molar mass = 142 g/mol

0.24 = mass/142

1.5 L

Mass = 0.24 (1.5)(142) =