Unit Eleven Powerpoint

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Unit Eleven: Solutions
Solutions
• A solution is a homogeneous mixture of two or more
substances
▫ Homogeneous – uniform characteristics throughout
▫ Heterogeneous – different compositions; various
throughout
• Solutions have at least two components
▫ Solutes – the minority component
▫ Solvents – the majority component
▫ 75% isopropyl solution – solute is water, solvent is
isopropyl
▫ 3% H2O2 – solute is H2O2, solvent is water
Nine types of mixtures
Solute
Solvent
Examples
**Gas
Gas
Air
**Gas
Liquid
Soda
Gas
Solid
Styrofoam or marshmallows
Liquid
Gas
Clouds
**Liquid
Liquid
Alcohol in water
Liquid
Solid
Mercury on penny (amalgam)
Solid
Gas
Smoke
**Solid
Liquid
Sugar or salt in water (Liquid is usually solvent)
**Solid
Solid
Coins, gemstones, alloys
- ** means common type of solution
- Amalgam: an alloy of mercury and another metal
- Likes Dissolves Likes
Non-Solutions - Suspensions
• Suspensions
▫ A mixture from which particles settle out upon
standing
▫ Particles are larger than in a solution
▫ Suspended – temporarily out of school
▫ Examples: Italian Dressing, muddy water, orange
juice with pulp
Non-Solutions - Colloids
• Colloids
▫ A permanent mixture whose particles are smaller
than in a suspension and larger than in a solution
▫ Particles will reflect light, cloudy appearance
▫ Do not settle out and cannot be filtered
▫ Milk, starch, dusty air, fog
Name
Particle Size
Permanence Examples
Solution
d < 1 nm
Permanent
Sugar-water, acids, bases, salt
water
Colloid
1 nm < d < 100nm
Permanent
Milk, blood, mayonnaise
Suspension
d > 100 nm
Settles Out
Mud, clay, cement
Property
Solutions
Colloids
Suspensions
Settling Out
Do not settle
Do not settle
Settle on standing
Filtering
Unchanged
Unchanged
Separates when
filtered
Tyndall Effect
Do not scatter light
Scatters light
Scatters light
Effect on Colligative
Properties
Does affect
Does not affect
Does not affect
Tyndall Effect
Laser pointed through a solution, colloid, and
suspension – what will happen?
Non-Electrolyte
• Aqueous solutions containing a solute that
dissolves as molecules
• Do not conduct electricity
• CH3OH  CH3OH
• C12H22O11  C12H22O11
Electrolyte
• Aqueous solutions containing a solute that
dissociates into ions
• Conducts electricity
• NaCl  Na1+ + Cl1- or Al2(SO4)3  2Al3+ + 3SO42• Strong electrolytes have large portions of solute
existing as ions
• Weak electrolytes have a fraction of the solute
existing as ions
Solubility
• Solubility is the amount of compound (usually in
grams) that will dissolve in a certain amount of
liquid
• There are three types of solutions:
▫ Unsaturated
▫ Saturated
▫ Supersaturated
Solubility
• Saturated Solutions
▫ Hold the maximum amount of solute under the solution conditions
▫ If additional solute is added to a saturated solution, it will not dissolve
• Unsaturated Solutions
▫ Hold less than the maximum amount of solute under the solution
conditions
▫ If additional solute is added to an unsaturated solution, it will dissolve
• Supersaturated Solutions
▫ Hold more than the normal maximum amount of solute
▫ Any disturbance will precipitate the solute or make it come out of
solution
Supersaturated Solution
Example: Rock Candy
Solubility Curves
• 35 grams of NaCl per 100
grams at 25°C is a __ soln.
• 25 g of KNO3 per 35 g of
water at 50°C is a ___ soln.
• 45 g of KNO3 per 100 g of
water is cooled from 40°C
to 0°C
Solubility
• Solubility depends on:
▫ Identity of solute and solvent
 Like dissolves like -> polar dissolves polar and
nonpolar dissolves nonpolar
▫ Temperature
 For solids in liquids, solubility increases with
increasing temperature
 For gases in liquids, solubility decreases with
increasing temperature
Solubility
▫ Pressure
 For solids in liquids, a change in pressure has very
little effect on the solubility
 For gases in liquids, higher pressure increases the
solubility of the gas in the liquid
 When a can of soda is opened,
there is less pressure so the gas
is less soluble
• Worksheet One is due Friday (Tomorrow)
• Worksheet Two is due Monday
▫ Skip Question 10
▫ Questions 3, 4, and 5 you cannot answer until
Friday’s notes
Solubility
• Rate of solution –
▫ How fast a substance dissolves and how quickly
the substance goes into solution
▫ Factors that increase the rate of solution for solids
 Decrease particle size
 Stirring
 Increase temperature
Hydration versus Solvation
• Hydration
▫ A solute is dissolved by water molecules attaching
to ions and moving them into solution
• Solvation
▫ Process of molecules of a solvent moving
molecules or ions into solution
Concentrations
• Concentrations – the amount of solute in a
solution
▫ A dilute solution is one containing small amounts
of solute relative to solvent
▫ A concentrated solution is one containing large
amounts of solute relative to solvent
▫ Mass percent, molarity, and molality
Mass Percents
• Mass Percents – the number of grams of solute per
100 grams of solution
Mass percent=(mass of solute)/(mass of solution)x100
Practice Problems
• Calculate the mass percent of NaCl in a solution
containing 15.3 grams of NaCl and 155.0 grams H2O.
• Calculate the mass percent of a solution containing
27.5 grams C2H6O and 175 mL of H2O
• A soft drink contains 11.5% sucrose by mass. What
volume of soft drink solution, in mL, contains 85.2
grams of sucrose?
Molarity
• Molarity – the number of moles of solute per liter of
solution
• A concentration of 6 M
HCl contains 6 moles of
HCl per 1 L of solution
• Molar solutions are
prepared in a volumetric
flask
• Molarity = M = moles of solute/liters of solution
Practice Problems
• Calculate the molarity of a sucrose solution
made with 1.58 moles of solute diluted to a total
volume of 5.0 L of solution.
• Calculate the molarity of a solution made by
putting 15.5 grams of NaCl into a beaker and
adding water to make 1.50 L of NaCl solution.
Practice problems
• 6.7 grams of NH4Cl is dissolved in enough water to
make 803 mL of solution. What is the molarity of
the solution.
• How many grams of NaOH are needed to make
500.0 mL of a 1.00 M solution?
• What volume of a 1.0 M NaNO3 solution can be
prepared from 170.0 grams of NaNO3?
Solution Dilutions
• Most solutions are bought as stock solutions,
however most labs need diluted solutions.
• We use M1V1=M2V2
Practice Problems
• A laboratory procedure calls for 5.00 L of a 1.50
M KCl solution. How should you prepare this
solution from a 12.0 M stock solution?
• To what volume should you dilute 0.100 L of a
15 M NaOH solution to obtain a 1.0 M NaOH
solution?
Practice Problems
• How much 6.0 M NaNO3 solution should be
used to make 0.585 L of a 1.2 M NaNO3
solution?
Solution Stoichiometry
• Tying it all together!
How much 0.125 M NaOH solution is required to
completely neutralize 0.225 L of 0.175 M H2SO4
solution?
H2SO4(aq) + 2 NaOH(aq) → Na2SO4(aq) + 2 H2O(l)
Solution Stoichiometry
• How much 0.115 M KI solution in liters is
required to completely precipitate the lead in
0.104 L of 0.225 M Pb(NO3)2?
2 KI(aq) + Pb(NO3)2(aq) → PbI2(s) + 2 KNO3(aq)
Solution Stoichiometry
• How many milliliters of 0.112 M Na2CO3 are
necessary to completely react with 27.2 mL of 0.135
M HNO3 according to the following reaction?
2HNO3(aq)+ Na2CO3(aq) → H2O(l)+ CO2(g)+ 2NaNO3(aq)
Molality
• Molality – is the number of moles of solute per
kilograms of solvent
• A concentration of 6 m HCl contains 6 moles of HCl per 1
kg of solvent
• To make 1 liter of 1 m solution, one mole is added to
enough water to make 1 L
• Which is more concentrated 1.0 m or 1.0 M?
▫ 1.0 M
• Molality = m = moles of solute/kg of solvent
Practice Problems
• What is the molality of the solution if 5.0 grams
of KI are in 500.0 grams of water?
• How many grams of calcium nitrate (Ca(NO3)2)
must be added to 20.0 grams of water to make a
2.5 m solution?
Colligative Properties
• A property that depends on the number of solute
particles and not the type of solute particles
• How much you have not what you have
• Two types
▫ Freezing point depression
▫ Boiling point elevation
▫ These depend on quantity of solute not type of solute
Colligative Properties
• Freezing point depression – difference in
temperature between the freezing point of a solution
and the freezing point of the pure solvent
▫ Solute disrupts the formation of the orderly pattern
thus requiring more energy
 Solution freezes at a lower temperature than the pure
solvent
▫ Magnitude is proportional to the number of solute
particles dissolved
ΔTf = Kf • m • (# of particles)
• ΔTf = change in temperature
• Kf = molal freezing point depression constant
• m = molality
• (# of particles) = how many particles of solute form
in solution
Colligative Properties
• Boiling point elevation – difference in temperature
between the boiling point of a solution and the
boiling point of the pure solvent
▫ Nonvolatile solute dissolved in the solvent disrupts the
vapor pressure which increases the boiling point
 Solution boil at a greater temperature than the pure
solvent
▫ Magnitude is proportional to the number of solute
particles dissolved
ΔTb = Kb • m • (# of particles)
• ΔTb = change in temperature
• Kb = molal boiling point depression constant
• m = molality
• (# of particles) = how many particles of solute form
in solution
Practice Problems
• What is the freezing point depression and the
boiling point elevation of a pinch of salt (0.25
grams NaCl) in a 2.00 L aqueous solution?
Kf=1.86°C/m
Kb=0.512°C/m
Practice Problems
• What is the freezing point depression and boiling
point elevation of a 0.40 m solution of sucrose in
ethanol?
Kf=1.99°C/m
Kb=1.22°C/m
F.p.=-114.6°C
B.p.=78.4°C
• Unit Eleven Test Tomorrow (Friday March 8th)
• Worksheet Five due Tomorrow
• Gizmo’s due Tomorrow
• Lab Report Revisions due Tuesday
▫ Will have optional computer time on Monday

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