SOLUTIONS A mixture worth getting your hands wet in.
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Transcript of SOLUTIONS A mixture worth getting your hands wet in.
SOLUTIONSSOLUTIONS
A mixture worth getting your A mixture worth getting your hands wet in.hands wet in.
SOLUTIONS UNIT SKILLSSOLUTIONS UNIT SKILLS
• Determine if a mixture is a solutionDetermine if a mixture is a solution• Describe how various factors affect solubility and Describe how various factors affect solubility and
the rate of solutionthe rate of solution• Interpret data on solubility curvesInterpret data on solubility curves• Distinguish between saturated, unsaturated, Distinguish between saturated, unsaturated,
supersaturated, concentrated, and dilute solutionssupersaturated, concentrated, and dilute solutions• Solve problems that involve concentrations of Solve problems that involve concentrations of
solutionssolutions• Describe the relationship between solute Describe the relationship between solute
concentration and change in the boiling and concentration and change in the boiling and freezing points of a solventfreezing points of a solvent
Solution TerminologySolution Terminology
•Solution– homogeneous mixture
•Solute – substance dissolved in another substance
•Solvent – substance that dissolves the solute
•Aqueous – solution in which water is the solvent
•Tincture – solution in which alcohol is the solvent
Solution CharacteristicsSolution Characteristics•Homogeneous mixtures•The dissolved particles will not settle
out of the solution•Light can pass unobstructed through
the solution•Filtration will not separate out the
solute•Considered to be a single phase even
if started as two different phases
Types of SolutionsTypes of Solutions• Gas Solutions – two or more gases mixed together• Liquid Solutions
A. Solid dissolved in a liquidB. Liquid dissolved in a liquidC. Gas dissolved in a liquid
• Solid Solutions – two or more solids mixed togetherA. Alloy – solid solution of two or more metals
examples:B. Amalgam – alloy in which mercury is one of the
metalsT yp es o f S o lu tio ns
G a s S o lu tio nsT w o o r m o re g a ses
m ixed to g e th er
S o lid d isso lve d in a liq u id L iq u id d isso lve d in a liq u id G a s d isso lve d in a liq u id
L iq u id S o lu tio ns
A llo yS o lid so lu tio n o f tw o
o r m ore m e ta ls
A m a lg amA llo y in w h ich m e rcu ry
is o ne o f th e m e ta ls
S o lid S o lu tio nsT w o o r m o re so lids
m ixed to g e th er
S o lu tio n Typ es
Solubility
• We need to find out about the process of dissolving so we can predict...
• Why certain substances dissolve in water.
Ionic compounds dissolving:
In the case of sodium chloride, as with many other ionic compounds, when they dissolve in water, they disperse randomly and also become strong electrolytes.
Solubility is affected by the strength of the solute-solute attractions as well as the solute-solvent attractions.
Solubility of polar substances
• Water is able to dissolve non-ionic substances also like sugar.
• Also ethanol.• Why? When water is a very polar
molecule.• We have to look at the substance
itself. It must be compatible with water.
The ethanol molecule contains a polar O—H bond.
Ethanol can form
hydrogen bonds with
water molecules.
The polar water molecule interacts strongly with the polar O—H bond in ethanol.
Do you see where the sugar molecule might be attracted to
water?
Can you see any places for water to be attracted to petroleum?
We know from experience that oil and water don’t mix. They are insoluble or immiscible.( 2 liquids that are mutually insoluble)
“Like dissolves like”
Characteristics of Solutions
HomogeneousSolute will not settle out as long as conditions aren’t changed.Light passes throughFiltration will not separateOne phase
http://www.youtube.com/watch?v=NxldP1wK-f4
Examples of types of solutions
State of solution
State of solute
State of solvent
Example
Gas Gas Gas Air, natural gas
Liquid Liquid Liquid Antifreeze in water
Solid Solid Solid Brass
Liquid Gas Liquid Soda, carbonated
Liquid Solid Liquid Seawater, sugar water
SolubilityAmount of solute that can dissolve in a solvent
•Temperature – higher solubility at higher temperatures. Except gases dissolved in a liquid. Behave the opposite way.
•Polarity of solute and solvent. Like dissolves like. Example: vitamins
•Pressure – mainly affects gaseous solutes. Higher pressure more gas can dissolve.
Rate of SolutionRate of Solution How quickly a solute How quickly a solute dissolvesdissolves• Size of the solute particlesSize of the solute particles
• StirringStirring
• Amount of solute already dissolvedAmount of solute already dissolved
• TemperatureTemperature
Solution Concentrations
• We have some very general descriptions:– Saturated: solution contains as much solute as in
can at that temp.– Unsaturated: when more solute can be added and
dissolves– Supersaturated: solution contains more dissolved
solid than saturated solution. Very unstable– Concentrated: relatively large amount of solute
present– Dilute: relatively small amount of solute is
dissolved
• And then some more specific descriptions:– Mass Percent --Density – Molarity– Molality– Normality
Mass Percent
Mass percent = Mass of soluteMass of solution
x 100
Suppose a solution is prepared by dissolving 1.0 g of sodium chloride in 48 g of water. The solution has a mass of 49 g total. Find the mass percent of the solute.
1.0 g solute49 g solution
x 100 = 2.0% NaCl
Although milk is not a true solution, it does contain dissolved sugar called lactose. Cow’s milk typically contains 4.5% by mass of lactose, C12H22O11. Calculate the mass of lactose present in 175 g of milk.
Mass of solution (milk) = 175 gMass percent of solute (lactose) = 4.5%
Mass percent = Mass of soluteMass of solution
x 100%
4.5% = X (unknown g solute)175 g solution
x 100%100%
175 g
X = 7.9 g solute (lactose)
Molarity
The units we show as either:
M
M = Moles solute Liters of solution
Since we deal with solutions a lot, a more convenient measure of concentration is Molarity.
Or mol L
Calculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH in enough water to make 1.50 L of solution.
M = Moles solute Liters of solution
11.5 g NaOH 1 mol NaOH40.0 g NaOH1.50 L solution
= 0.192 M NaOH
Calculate the molarity of a solution prepared by dissolving 1.56 g gaseous HCl into enough water to make 26.8 mL of solution.
M = Moles solute Liters of solution
1.56 g HCl 1 mol HCl36.5 g HCl26.8 mL solution
= 1.59 M HCl1000 mL 1 L
Molality
m = Moles solute kg solvent
Density
d = Grams solutemL solution
Preparing a Standard Solution
1. Calculate # g of solute.
2. Put a little distilled water in the flask.
3. Put solute in flask, dissolve.
4. Fill to the mark.
Making a Standard Solution
To analyze the alcohol content of a certain substance, a chemist needs 1.00 L of an aqueous 0.200 M K2Cr2O7 solution. Give directions to mix.
1.00 L soln 0.200 mol K2Cr2O7
1 L294.2 g K2Cr2O7 1 mol
=58.8 g K2Cr2O7
3. Put K2Cr2O7 in flask, dissolve.
2. Put small amount of distilled water in 1 L flask.1. Weigh out 58.8 g K2Cr2O7
4. Fill to the mark with distilled water.
DilutionSometimes, concentrated solutions are purchased. Water is added to achieve the desired molarity for a particular solution.
M1V1 = M2V2
Prepare 500. mL of 1.00 M acetic acid (HC2H3O2) from a 17.5 M stock solution.
(17.5 M)V1=(1.00 M)(500 mL)
V1 = 28.6 mL
How many moles of Ag+ ions are present in .025 L of a 0.75 M AgNO3 solution?
.025 L 1 mol Ag+ ions1 mol AgNO3
= .019 mol Ag+
0.75 mol AgNO3
1 L
Remember: 1 mole of AgNO3 = 1 mole Ag+ ions
Properties of Solutions:boiling & freezing points
• What does adding NaCl to a pot of boiling water do?
• Why do we spread “ice melt” on our sidewalks in the winter?
• Why do we add “antifreeze” to our car radiators?
• Adding a solute to a solvent changes the vapor pressure of the solution....thus changing the boiling and freezing points!
Boiling in a pure solvent
Those solvent molecules in the
bubble have enough energy to break all
intermolecular attractions
When a solute is added: It may be
argued that the solute
reduces the number of
solvent molecules
that can get into the bubble.
Thus it takes more energy (heat) to “boil” the solvent....this is the “boiling
point elevation”
Freezing point is also affect by the addition of a solute.
At the point of freezing & melting, the vapor pressures of the solid and liquid are at equilibrium.
Since adding a solute lowers the vapor pressure of a substance, the vapor pressure of a liquid is equal to that of the solid at a lower “temperature”.
These properties— boiling point freezing point vapor pressure osmotic pressure of solvent
--are called
Colligative Properties
Freezing Point DepressionFreezing Point Depression
Normal freezing point occurs at a temperature where the vapor pressure of the solid and liquid are equal to each other.
Tf = Kf m solute
Kf is the freezing point constant for the solvent.
Normal freezing point occurs at a temperature where the vapor pressure of the solid and liquid are equal to each other.
The solid does not form until the temperature is lower than in the pure solvent.
We say that a non-volatile solute depresses the freezing point of a solution and can calculate it with:
The solid does not form until the temperature is lower than in the pure solvent.
11.9 What mass of ethylene glycol (C2H6O2) must be added to 10.0 L water to produce a solution for use in a car’s radiator that freezes at -10.0 oF (-23.3oC)? Assume the density of water is exactly 1 g/mL.
Tf = Kf m solute
T = 23.3oC
Kf = 1.86oC kg/mol
10.0 kg solvent used
23.3oC = (1.86oCkg/mol) m solute
msolute=12.53 mol C2H6O2
kg solvent 10 kg water
= 125.3 mol C2H6O2
125.3 mol C2H6O2
= 7769 g
62 g C2H6O2
1 mole
OsmosisOsmosis
•A semi-permeable membrane separates a solution and pure solvent—allowing the solvent but not the solute to pass.
•Osmosis is the flow of solvent to the solution until the solution reaches equilibrium
•Osmotic pressure is the hydrostatic pressure on the solution and depends on the concentrations….