CORNELL NOTES
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Transcript of CORNELL NOTES
CORNELL NOTESCORNELL NOTES
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SOLUTIONSSOLUTIONSA solution is a homogeneous mixture; particles are evenly distributed throughout the mixture.• Proportions may vary• Uniform ratio throughout the mixtureA liquid solution is clear. The particles are not visible, do not settle, and can not be filtered.
A solution differs from a suspension in that the particles of a suspension are visible, can be filtered, and settle.
A solution differs from a colloid in that the particles of a colloid exhibit Tyndall effect., yet do not settle.
(TYNDALL effect: the scattering of light by particles such as headlights in fog, flashlight through Jello or dilute milk)
A solution will not exhibit the Tyndall effect.
SOLUTIONS SolnsSOLUTIONS Solnshomogeneous mixtureevenly distributed particles• variable proportions• uniform ratio Liq soln clear. particles are not visible, do not settle,
and can not be filtered. Not suspensions: particles of a susp are visible, can
be filtered, and settle. Not colloids: particles of a colld show Tyndall effect.,
yet do not settle. (TYNDALL effect: the scattering of light by particles
such as headlights in fog, flashlight dilute milk) A soln will not exhibit the Tyndall effect.
SOLUTIONS SolnsSOLUTIONS Solnshomogeneous mixtureevenly distributed particles• variable proportions• uniform ratio liquid soln clear. particles are not visible, do not settle,
and can not be filtered. Not suspensions: particles of a susp are visible, can
be filtered, and settle. Not colloids: particles of a colld exhibit Tyndall
effect., yet do not settle. (TYNDALL effect: the scattering of light by particles
such as headlights in fog, flashlight dilute milk) A solution will not exhibit the Tyndall effect.
Define soln
Describe soln
Are all solns liquid?
Contrast liquid soln with susp and colloids
SOLUTIONS SolnsSOLUTIONS Solnshomogeneous mixtureevenly distributed particles• variable proportions• uniform ratio liquid soln clear. particles are not visible, do not settle,
and can not be filtered.
Not suspensions: particles of a suspension are visible, can be filtered, and settle.
Not colloids: particles of a colloid exhibit Tyndall effect., yet do not settle.
(TYNDALL effect: the scattering of light by particles such as headlights in fog, flashlight dilute milk)
A solution will not exhibit the Tyndall effect.
Define solution
Describe solution
Are all solns liquid?
Contrast liquid solution with suspensions and colloids
Solutions are homogenous mixtures with variable proportions and uniform ratios. Separate components are not visible/discernible.
Cherry Kool-aidCherry Kool-aidRed powder: flavor and colorWhite crystals: sugarClear liquid: water
One substance dissolved in another◦Solute: the substance being dissolved◦Solvent: the substance that dissolves
the solute Sugar is the SOLUTE (smaller quantity) Water is the SOLVENT (larger quantity)
Types of SolutionsTypes of SolutionsGas (solvent is gas)
◦ Gas into Gas: air◦ Liquid into Gas: humidity◦ Solid into Gas: air pollution
Liquid (solvent is liquid)◦ Gas into Liquid: pop◦ Liquid into Liquid: vinegar◦ Solid into Liquid: sweet tea
Solid (solvent is solid)◦ Gas into Solid: absorbent charcoal◦ Liquid into Solid: dental fillings◦ Solid into Solid: alloys of metal
The Dissolving ProcessThe Dissolving ProcessTwo factors affect the dissolving
process: dissolution◦The constant motion of the particles
(There’s that good old kinetic molecular theory again!)
◦The polarity of the solute and solvent (Recall that polarity is when a compound has partial charges because of uneven distribution of charges)
Steps of the Dissolving Steps of the Dissolving ProcessProcess1. Moving solvent particles cluster
around solute molecules or particles at the surface of the solid.
2. Solvent molecules pull solute off of the solid surface and into solution.
3. Moving solvent particles continue to spread solute evenly throughout the solution,
The process repeats itself as fresh layers of the solute are exposed.
1. Solvent particles cluster around solute particles at the surface.
2. Solvent particles pull solute particles away from surface, into solution.
3. Moving solute particles continue to spread solute evenly through solution.
MOLECULAR
1. Solvent particles cluster around solute particles at the surface.
2. Solvent particles pull solute particles away from surface, into solution.
3. Moving solute particles continue to spread solute evenly through solution.
IONIC
IONIC COMPOUNDSIONIC COMPOUNDSWhen an ionic substance dissolves in
water, the forces of the solvent pulling on the ions is stronger than the forces holding the ions together.
The ions separate. This is called DISSOCIATION
Because charged ions are present in an ionic solution, ionic solutions conduct electricity and are called ELECTROLYTES.
EXAMPLE: NaCl
MOLECULAR COMPOUNDSMOLECULAR COMPOUNDSCertain polar substances form
ions when they dissolve in water. This process is called IONIZATION.
Because ions are formed, the solution conducts electricity.
These substance are also ELECTROLYTES.
EXAMPLE: HCl, HC2H3O2
MOLECULAR COMPOUNDSMOLECULAR COMPOUNDSOther polar substances do not
ionize in water.Because ions are not formed, the
solution does not conduct electricity.
These substances that do not ionize in water and do not conduct electricity are called NON-ELECTROLYTES.
EXAMPLE: sugar
ELECTROLYTES: ELECTROLYTES: substances that conduct substances that conduct electricity when dissolved in waterelectricity when dissolved in water
Ionic substances that separate into ions (dissociate) or polar molecular substances that form ions (ionization) when dissolved conduct electricity and are called ELECTROLYTES.
Factors Solid in Liquid
Gas in Liquid
TEMPERATURE Temp > Rate >
Temp > Rate <
AGITATION Agitation > Rate >
Agitation > Rate <
SIZE OF PARTICLES
Size < (surface area
>) Rate >
NA
PRESSURE NA Pressure > Rate >
WHY? The solute particles are
less energetic than solvent
The solute particles are
more energetic than
solvent
FACTORS THAT AFFECT THE RATE OF DISSOLUTION
Think BIGRecall the Pop and Mentos experiment!
The pop “explodes” because the dissolved gas rapidly leaves the solution because the
candy gives it surfaces to collect on (nucleation sites).
Particles in SolutionsParticles in SolutionsSolvents with non-polar molecules
dissolve non-polar substances◦Oil, grease, dry cleaning fluid, paint,
turpentineSolvents with polar molecules
dissolve polar substances◦Water dissolves sugar, ionic
compounds
LIKE DISSOLVES LIKE
TermsTermsSoluble: capable of being
dissolved in a particular solventInsoluble: incapable of being
dissolved in a particular solvent
Miscible: liquids that dissolve freely in any proportion
Immiscible: liquids that are not soluble in each other
Detergents and Detergents and emulsifiersemulsifiersGrease is non-polarWater is polar
DETERGENT has ◦A non-polar end that dissolves the
grease◦A polar end that dissolves in the
water to rinse it away NONPOLAR DETERGENT
POLARGREASE WATER
ReviewReviewA substance whose water solutions
do not conduct electricity is a non-electrolyte.◦Many covalent compounds
A substance that separates into ions (dissociates) or forms ions (ionizes) in a water solution conducts electricity and is called an electrolyte◦All ionic and some covalent compounds
SolubilitySolubilityThere are limits to the amount of
solute that will dissolve in a given amount of solvent at a given temperature
There are some general terms:◦Unsaturated◦Saturated◦Super-saturated
UnsaturatedUnsaturateda solution that can dissolve more
of a given solute at a certain temperature◦A crystal of solute added to an
unsaturated solution will dissolve When you add a second spoon of sugar
to your cup of tea, it dissolves. The tea was an unsaturated solution.
SaturatedSaturateda solution that has dissolved all of the
solute that it can at a certain temperature◦ A crystal of solute added to a saturated
solution will drop to the bottom, un-dissolved. When you add three spoons of sugar to your tea,
some sugar drops to the bottom, undissolved. It is a saturated solution.
DYNAMIC EQUILIBRIUM exists: ◦ changing but balanced.◦ Some solid dissolves, but as some dissolves,
some re-crystallizes
Super-saturatedSuper-saturatedan unstable solution that contains more
solute than a saturated solution at a certain temperature◦ A crystal of solute added to a super-
saturated solution will cause crystallization. So will any disruption of the unstable solution.
◦ Make a saturated solution at an elevated temperature and cool it slowly. At the lower temperature, the solute will remain dissolved in an unstable situation. If disrupted, the solute crystallizes. Hot-packs and rock candy
Max g of solute that will dissolve in 100 g of solvent at a given temperature
Concentration: Concentration: the amount of the amount of solute in a given amount of solvent solute in a given amount of solvent or solutionor solutionDilute: a relatively small amount
of solute in a relatively large amount of solvent
Concentrated: a relatively large amount of solute in a relatively small amount of solvent
We can do better!
Percent by volumePercent by volumemL of solute /100 mL of solution
Percent by massPercent by massg of solute/100 mL of solution
Mass per volumeMass per volumeg solute/1000 mL solution
PPM and PPBPPM and PPBx/1,000,000x/1,000,000,000
Serial dilutions are often used◦1x, 10x, 100x, 1000x, etc.
MolarityMolarityM = mol solute/liter of solution
Chemists use this because it lets us work concentration into stoichiometry problems
MolalityMolalitym = mol solute/kg of solvent
Chemists sometimes use this because volume of liquids changes with temperature. Soon, we will be studying the effect of concentration as temperature changes.
Dilutions: Dilutions: a concentrated solution is diluted a concentrated solution is diluted by adding more solvent to get the desired by adding more solvent to get the desired concentration. concentration. M1V1 = M2V2
Moles before dilution = Moles after dilution
◦ M = molarity = mol/L◦ V = volume = L
◦M x V = mol/L x L = # mol of soluteThe # of moles before dilution is equal to the # of
moles after dilution. The same # of moles is present in more solvent. The concentration (M, molarity) changes, the volume (V) changes, but not the # of moles of solute (M x V). ◦ Volume units may vary from L, but must be consistent within problem.
So, M1V1 = M2V2