sec. 15.1 solutions - typepad · solubility curve – shows saturated solutions 1) ... find molar...
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SOLUTION Definition:
Homogeneous mixture of 2 or more substances
Ex. salt water, tea
Homogeneous – Can’t distinguish parts of solution.
All in 1 phase
PARTS OF A SOLUTION Solute - Substance being
dissolved Salt
Solvent - Dissolving medium Water – aqueous solution Isopropyl alcohol
Water is the universal solvent.
Liquid solutions are clear!
SOLUTIONS CAN EXIST IN ALL PHASES:
Air – Gaseous solution
Alloy – Solid solution (Brass = Cu + Zn)
Most solutions are
liquids
In all gas or all liquid
solutions, the smaller
amount is the solute!
Seawater is a solution
SOLUBILITY TERMS: Soluble – Substance
dissolves in another substance
Sugar in water
Insoluble – Does not
dissolve in substance Sand in water
Miscible – 2 liquids soluble in each other
Alcohol & water
Immiscible – 2 liquids are insoluble
Oil & water – form layers
SOLVATION IN AQUEOUS SOLUTIONS
Solvation – Solvent particles surround solute to
form a solution.
Hydration – Solvation with water
“LIKES DISSOLVE LIKES”
Predict which will dissolve in each other:
water (polar)
octane (nonpolar)
sugar (polar)
NaF (ionic)
benzene (nonpolar)
Sugar and NaF are soluble in water
Octane & benzene are soluble
• Polar substances dissolve
in polar substances
• water & alcohol or
ionic substances (NaCl)
• Nonpolar substances
dissolve in nonpolar
substances
oil & gasoline
FACTORS THAT INCREASE SOLVATION:
1) Stirring
2) Increase surface area (crush)
3) Increase temperature of solvent
HEAT OF SOLUTION Exothermic
Releases heat - gets warm
NaOH + water
Endothermic
Absorbs heat – gets cool
Cool
← Ammonium nitrate
SOLUBILITY – Maximum amount solute that will dissolve in given amount of solvent at a certain temperature
Saturated – Solution contains maximum amount of dissolved solute for given amount solvent (given temp. & pressure)
Unsaturated – Contains less
Solute than the solvent can hold
(Can dissolve more solute)
Saturated solution:
(Additional solute falls to bottom)
SATURATED SOLUTIONS ARE IN EQUILIBRIUM
SUPERSATURATED SOLUTIONS: Contains more dissolved
solute than a saturated solution at the same temperature
Unstable
May recrystallize if disturbed
Ex. Sweet tea – Made by heating water, adding more solute, then cooling down.
FACTORS AFFECTING SOLUBILITY:
Temperature Solubility of a solid - Increases when temperature
increases -Sugar & water
Solubility of a gas – Decreases when temperature increases - Oxygen & water
SOLUBILITY CURVE – Shows saturated solutions
1) How much KCl
(potassium chloride)
will dissolve in 100 g water at 90°C?
54 g KCl
2) At what temperature
will 10 g of KClO3
(potassium chlorate)
dissolve in 100 g water?
30°C
SOLUBILITY CURVE Saturated, Unsaturated or Supersaturated?
3) If 50 g KCl is dissolved in 100 g water at 90°C, describe the solution.
How much additional KCl was added?
4) If 70 g CaCl2 is dissolved in 100 g water at 10°C, describe the solution.
How much extra CaCl2 was added?
SOLUBILITY CURVE FOR OXYGEN What happens to
solubility of O2 as temperature rises?
Suppose a company dumps warm, clean water in a lake.
What might happen to the fish?
Explain how this might affect the food chain.
Solubility Curve for Oxygen Gas in Water
0
5
10
15
0 10 20 30 40 50
Temperature (degrees Celsius)
mg
of
oxy
ge
n d
iss
olv
ed
in 1
00
0g
of
wa
ter
Series1
PRESSURE & SOLUBILITY (Gases only)
Henry’s Law – Solubility directly proportional to pressure
S1 = S2 P1 P2
Pressure does not affect
solubility of solids & liquids.
Ex. Soft drink – bubbles when open
CO2 most soluble when drink
is cold & at high pressure – unopened.
HENRY’S LAW If 0.85g of gas at 4.0 atm pressure dissolves in 1.0L water at 25ºC, how much will dissolve at 1.0 atm and at the same temperature?
S1 = S2
P1 P2
S1 = 0.85 g/L
S2 = ? g/L
P1 = 4.0 atm
P2 = 1.0 atm
0.85g/L = S2
4.0atm 1.0atm
(0.85g/L)(1.0)=(S2)(4.0)
S2 = (0.85g/L)(1.0)
(4.0)
S2 = 0.21 g/L
HENRY’S LAW
2 L bottle 2 L bottle
after opening before opening
and pouring and pouring
What factors (T&P) would increase solubility of sugar & carbon dioxide when making a soft drink?
To dissolve more sugar (solid), increase temperature
To dissolve more CO2 (g), decrease temperature, increase pressure
SOLUTE VS. SOLVENT
Water is the universal solvent
SOLUTION CONCENTRATION: The amount of solute dissolved in a specific amount of solvent or solution.
Concentrated – contains large amount solute
Dilute – contains small amount solute
MOLARITY (MOLAR CONCENTRATION)
2) MOLARITY (M) – Number moles of solute
dissolved per liter of solution.
Molarity (M) = moles solute(n)
liters solution
To make 1 Molar solution of NaCl Dissolve 1 mole (58.55 g) of NaCl
in water to the line of a 1 liter volumetric flask
1 mole NaCl = 23.00 + 35.45
= 58.55 g
PROBLEM: Find molar concentration (molarity) of 100. mL of a solution containing 0.075 mol of dissolved NaCl.
M = # moles solute
liters solution
#moles = 0.075 mol
#L = 100.mL x 1 L = 0.100 L
1000 mL
M = 0.075 mol 0.100 L
M = 0.75 mol/L
= 0.75 M
PROBLEM: Calculate the molarity of 500. mL of a
solution containing 0.400 moles HCl.
M = # moles(n) volume (L)
n = 0.400 mol volume = 500.mL x 1 L 1000 mL = 0.500 L
M = 0.400 mol = 0.800 mol/L 0.500 L
= 0.800 M
PROBLEM: What is the mass (g) of sodium hydroxide, NaOH in 2.00 L of a 0.25 M solution?
M = # moles
liters
# moles = M x liters
# mol = 0.25 mol x 2.00 L
L
= 0.50 mol NaOH
To find mass, multiply moles by molar mass!
0.50 mol NaOH x 40.00 g
1 mol
= 20.0 g NaOH
Molality (m): # of moles dissolved in each kilogram of solvent
m = moles of solute
kg of solvent
Independent of temp
Molality
Calculate the molality of a sol’n prepared by dissolving 20.4 g of sodium chloride in 192g of water.
m = moles of solute
kg of solvent
1. Convert 20.4 grams of NaCl to moles
2. Convert 192 g to kg
3. Divide moles by kg
What is the molality of a solid solution containing 0.125g of chromium and 81.3g of iron?
m = moles of solute
kg of solvent
.125 g Cr x 1 mole = .00240 moles Cr
52.00 g
81.3 g Fe x 1 kg = .0813 kg Fe
1000 g
m = .00240 moles = .0295 m
.0814 kg
EXPRESS CONCENTRATION AS MOLE FRACTION Mole fraction (X): # of moles of one
component divided by the total # of moles in the solution
X = moles of component
total moles of sol’n
Used to compare solute
and solvent
Solute + Solvent = Whole Solution
What are the mole fractions of ethyl alcohol (C2H5OH) and water in a solution prepared by adding 50.0g of ethyl alcohol to 50.0g of water?
50.0 g ethanol x 1 mole = 1.09 moles ethanol 46.08 g
50.0 g water x 1 mole = 2.77 moles water 18.02 g
Total moles = 1.09 + 2.77 = 3.86 moles
Mole Fraction = 1.09 moles ethanol = .282
3.86 moles
Mole Fraction = 2.77 moles water = .718
3.86 moles
DILUTING SOLUTIONS M1V1 = M2V2
What volume (mL) of concentrated (12.0 M) hydrochloric acid (HCl) solution must be used to make 0.500 L of a 3.00 M HCl solution?
M1V1 = initial (stock) M2V2 = final solution
12.0M x V1 = 3.00 M x 0.500 L
V1 = 3.00 x 0.500 L 12.0
= 0.125 L
= 125mL
COLLIGATIVE PROPERTIES
Vapor Pressure Lowering
Boiling Point Elevation
Freezing Point Depression
Osmotic Pressure
Physical properties of solutions that are affected by the number (not identity) of dissolved solute particles
ELECTROLYTES - Have greater effect on colligative properties - produce more particles. Electrolytes – Form ions in solution (ionic, acids) that conduct
electricity Ex. NaCl (s) Na+(aq) + Cl-(aq) 1 mol 1 mol 1 mol Note: 1 mole NaCl yields 2 moles of ions Acids (Start with H) HCl(g) H+(aq) + Cl-(aq) 1 mol 1 mol 1 mol Note: 1 mole HCl yields 2 moles of ions
Nonelectrolytes – Do not ionize (Don’t conduct - covalent) Ex. C6H12O6 (s) C6H12O6 (aq)
1 mole 1 mole
Note: 1 mol glucose yields 1 mol
*NaCl & HCl have greater effect on colligative properties
(1 mole yields 2 moles ions)
Which would have the greatest effect on colligative properties? 1 molal: Sucrose (C12H22O11) Mg(NO3)2 AlBr3
Sucrose (molecular): = 1 molecule
Mg(NO3)2 forms 1 Mg2+ and 2 NO3- = 3 ions
AlBr3 forms Al3+ and 3 Br- = 4 ions
AlBr3 has the greatest
effect on colligative properties
since most particles.
Sucrose
VAPOR PRESSURE: Pressure exerted in closed container by particles entering gaseous state.
Adding solute – Lowers solvent’s vapor pressure
Fewer solvent particles are at the surface, so less solvent vaporizes. Result: Lower vapor pressure
VAPOR PRESSURE – LOWERED BY ADDING SOLUTE
BOILING POINT ELEVATION In order to boil, vapor pressure must equal the
atmospheric pressure
When solute is added, vapor pressure is lowered.
Thus, solution must be heated to higher temperature.
Result: Boiling point increases
Adding salt to water when cooking
Salt raises boiling point of water when cooking pasta:
QUIZ 1. Colligative properties depend on the ___particles, not
the type.
2. Which has the greatest effect on the colligative properties: KCl C12H22O11 CaCl2 NO2 HCl
3. Vapor pressure is caused by particles in a ___ container entering the gaseous state. Adding a solute ___the vapor pressure.
4. ____occurs when the vapor pressure equals the atmospheric pressure. Adding a solute will ____the boiling point.
FREEZING POINT DEPRESSION
Adding solute lowers freezing point
Salt used on icy roads; making ice cream
Solids – have a high attraction between particles.
Adding a solute interferes with the
attraction between these particles.
OSMOTIC PRESSURE
Osmosis – diffusion of solvent particles across a semipermeable membrane (from higher to lower concentration)
Addition of solute causes water to move from the solvent (water) side to the solution side.
QUIZ 1) Adding a solute will ___ the freezing point. Give
2 practical applications of this.
2) a) Diffusion of solvent particles across a semi permeable membrane is called ____. Particles move from ______ concentration to ______ concentration.
b) Adding a solute causes water to move from the ____(water) side to the ____side of the membrane.
QUIZ
1) A solution is a ___mixture of 2 or more ___.
2) Homogeneous means that you cannot distinguish the ___ and it is in one ___.
3) Name the solutes and solvent in sweet tea.
4) ___is the universal solvent.
5) An example of a gaseous solution is ___.
6) An alloy is a solution made of ___. Give an example of an alloy.
7) In aqueous solutions, ___ is the solvent.
SOLUTION QUIZ
1) A substance that dissolves in another is ___.
2) Sand and water are ___.
3) Two liquids that are soluble are called ____.
4) Oil and water are ____.
5) Solvation with water is called _____.
6) “Likes dissolve likes” means that polar substances dissolve ___ and ___. Oil and water are insoluble because water is __ and oil is __.
QUIZ 1) Name 3 things that will increase solvation.
(Suppose you want to make Kool-Aid quickly).
2) When mixing calcium chloride and water, the solution gets warmer. This is ____.
3) A ___solution contains the maximum amount of solute at a given temperature (& pressure).
4) More solute can be added means the solution is___.
5) To make a supersaturated solution, ___ the solution, add more solute, then ___ it back down.
THE END
What is the molality of a solid solution containing 0.125g of chromium and 81.3g of iron?
m = moles of solute kg of solution .125 g Cr x 1 mole = .00240 moles Cr 52.00 g .125 g Cr x 1 kg = 1.25 x 10-4 kg Cr 1000 g 81.3 g Fe x 1 kg = .0813 kg Fe 1000 g Total kg = .0813 + 1.25 x 10-4 = .0814 kg m = .00240 moles = .0295 m .0814 kg
Calculate the molality of a sol’n prepared by dissolving 20.4 g of sodium chloride in 192g of water.
M = moles of solute
kg of solution
1. Convert 20.4 grams of NaCl to moles
2. Convert 192 g to kg
3. Divide moles by kg