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std 6

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Standard 6: Solutions
chapter 16
Chemistry
Ms. Siddall
Standard 6a: solution definitions
• Solution: a homogeneous mixture of 2 or
more substances in the same physical state.
• Properties:
– Particles are small
– Particles are evenly mixed
– Particles will not separate
• Examples:
– air (nitrogen & oxygen)
– Gatorade (water, sugar, etc)
– NaCl(aq) (salt & water)
Summary 1
• Is muddy water a solution? Why/why not?
• Solute: substance that is dissolved e.x. sugar
• Solvent: does the dissolving e.x. water
• Concentration: The amount of solute in a
given amount of solvent e.x. [HCl]
• (aq) = aqueous = A solution where water is
the solvent
Summary 2
Consider lemonade.
1. What is the solvent?
2. What are the solutes?
Standard 6b: Dissolving
Process
+
• Solvent: H2O
molecules with
dipole
+
-
• Solute: Ionic
crystal lattice
+
+
-
+
-
+
-
+
-
+
-
• Polar H2O
molecules surround
positive and
negative ions and
break apart crystal
lattice
• Water molecules
move away
(diffusion) so the
process is repeated
Show animation
Summary 3
Explain how water dissolves
ionic compounds
• It takes energy to break bonds
energy
Energy needed
to overcome
lattice energy
NaCl(s)
NaCl(aq)
Dissolving
Energy released
during dissolving
Summary 4
Does the energy diagram for
dissolving NaCl represent an
endothermic or exothermic
process? Explain your answer.
Saturated solution: A solvent can not dissolve any
more solute
• A saturated solution is at equilibrium. Particles are
dissolving and precipitating at the same rate
NaCl(s)  Na+(aq) + Cl-(aq)
Summary 5
Does the dissolving process
stop at equilibrium? Explain
why/why not.
Standard 6c:
Factors that affect the dissolving process
• Some factors affect solubility (how much
solute is dissolved)
• Some factors affect rate (how fast solute is
dissolved)
• Some factors affect rate and solubility
Standard 6c:
Factors that affect the dissolving process
Factors affecting how much solute is dissolved
1. Type of solvent / solute
• Polar solvents dissolve polar & ionic
solutes
• Non-polar solvents dissolve non-polar &
covalent solutes
e.x oil and water do not mix
Summary 6
Is oil a polar compound or a
non polar compound? How
do you know?
2. Temperature
• For solids: Temperature  solubility 
Temperature increases kinetic energy of
solvent particles therefore more solute can
be dissolved
• For gases: Temperature  solubility 
Temperature increases the kinetic energy
of solute particles therefore more particles
escape from solution
Summary 7
Why does the solubility of gas
in solution decrease with
increasing temperature?
Solubility of solids & gases
3. Pressure (Gasses Only!)
• Increasing pressure forces more gas into
solution
• Pressure  solubility 
low pressure
• Pressure  solubility 
High pressure
Gas
air
solution
Summary 8
Does the concentration of
carbon dioxide in your soda
increase or decrease when
you open the bottle? Why?
Factors that affect the rate of solubility
(how quickly something dissolves)
1. Temperature:
• T rate
• T rate
• Increasing temperature increases kinetic
energy = increased motion = increased
diffusion
2. Surface Area (particle size):
• S.A.  (particle size ) rate 
• S.A.  (particle size ) rate 
• Increasing surface area increases
opportunity for interaction between solute
and solvent
3. Stirring:
• stirring  rate 
• stirring rate 
• Stirring increases particle motion so more
particles can be dissolved at the surface of
the solid
Summary 9
1. Name one factor that
affects only solubility
2.Name one factor that
affects only rate
3.Name one factor that
affects rate and solubility
Standard 6d: calculations
• Molarity (mol/L)
Molarity = Moles solute
Liters solution
• Grams per Liter (g/L)
= Grams solute
Liters solution
• Percent Composition (%)
grams solute x 100%
grams solution
• Parts Per Million (ppm)
grams solute x 106
grams solution
Summary 10
A solution contains 80g of NaOH in
500ml of solution. Calculate:
1.‘grams per liter’
2. Molarity
3. percent composition
for the solution
• Using ‘Parts per Million’ (ppm)
• Usually used to measure solutions
containing a small amount of solute
• e.x air quality or drinking water quality
– Air contains about 1ppm CO2 (Every 1million
grams of air contains 1g CO2)
• smaller concentrations are measured in ppb
(parts per billion)
– Drinking water usually contains ≤ 0.5 ppb lead
Summary 11
Which solution has the highest
concentration of fluoride ions?
a) 10 ppm Fb) 100 ppm Fc) 10 ppb Fd) 100 ppb F-
• Example: What is the concentration (ppm)
of a 1L solution containing 5mg arsenic?
(The density of aqueous solutions = 1g/ml)
Standard 6e:
effect of solute on freezing and boiling point.
Molality (m) = moles solute
Kg solvent
e.x. what is the molality of a solution made by
dissolving 180g sugar (C6H12O6) in 500g water?
180g sugar 1 mol sugar 1000g
500g water
180g sugar
1 kg
= 2m
Summary 18
what is the molality of a solution made by
dissolving 92g ethanol (C2H6O) in 200g water?
92g ethanol 1 mol ethanol
200g water
46g ethanol
1000g
1 kg
= 20m
Freezing point depression and boiling point
elevation: adding solute to a solvent lowers
the freezing point and raises the boiling point
of the solvent.
• Solute particles disrupt crystallization and
evaporation.
• The change in freezing point or boiling point is
directly proportional to the molality of solute
particles.
• A solute that produces more ions in solution
has the greatest effect.
Summary 19
Explain why it takes more energy to boil water
when it has more solute particles dissolved in
solution.
3m sugar
3 moles NaCl produces
6m of solute particles
3moles CaCl2 produces
9m of solute particles
Summary 19
Which will affect the boiling point of solution
more? WHY?
a) 1m NaCl
b) 1m CaCl2
c) 1m AlCl3
6f: Chromatography and distillation.
Chromatography: the separation of solution
into individual substances using
differences in polarity.
e.x. DNA analysis
Distillation: separation of solutions into
individual substances using differences in
physical properties (boiling point)
e.x. salt water can be purified by distillation
Summary 20
Why is it possible to separate alcohols by
distillation?
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