i. the nature of solutions (p. 401 - 410, 425 - 433)
TRANSCRIPT
I. The Nature of SolutionsI. The Nature of Solutions
(p. 401 - 410, 425 - 433)(p. 401 - 410, 425 - 433)
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
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
• 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
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.
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!”