Transcript Slide 1

Solutions
Mechanisms and Phenomena,
Separations,
and
Concentration Problems
Solutions
How they form, What they do,
Separations,
and
Concentration Problems
Standards
• 6. Solutions are homogeneous mixtures of two or more
substances. As a basis for understanding this concept:
• a. Students know the definitions of solute and solvent.
• 6. b. Students know how to describe the dissolving process at
the molecular level by using the concept of random molecular
motion.
• 6. c. Students know temperature, pressure, and surface area
affect the dissolving process.
• 6. d. Students know how to calculate the concentration of a
solute in terms of grams per liter, molarity, parts per million, and
percent composition.
• 6. e.* Students know the relationship between the molality of a
solute in a solution and the solution’s depressed freezing point
or elevated boiling point.
• 6. f.* Students know how molecules in a solution are separated
or purified by the methods of chromatography and distillation.
Examples of
Chemical Change vs. Physical Change
Burning
Rusting
Bread Rising
Photosynthesis
Boiling
Freezing
Melting
Mixing
Salt dissolving in H2O
Salt precipitating from H2O
Chemical Change
Chemical changes occur when the atoms in
a substance change their electron
configurations.
Chemical changes are often noticeable due
to the appearance of a new substance or
the release or absorption of energy (light,
heat, electricity).
Reaction Symbols
Symbol
Meaning
(s), (l), (g) Substance is a solid, liquid, or gas
(aq)
Aqueous, substance is dissolved in H2O
“Produces” or “makes”
“Produces” through reversible reaction
heat or Δ
Heat is added to the reactants
Pt
A catalyst is used to speed up the
reaction
Definitions
• Heterogeneous – a mixture with large
particles (clumps of molecules or ions).
• Homogeneous – a mixture with very small
particles (individual molecules or ions).
• Solution – a homogeneous mixture of two or
more substances. (ex. salt in water)
Solvent – the main ingredient of a solution. (ex.
water)
Solute – the other ingredients dissolved into the
solvent. (ex. salt)
More Definitions
• Solution – a homogeneous mixture of two or
more substances. (ex. salt in water)
Solvent – the main ingredient of a solution. (ex.
water)
Solute – the other ingredients dissolved into the
solvent. (ex. salt)
• Colloid – a heterogeneous mixture of two or
more substances with medium-sized particles.
Usually stable. (ex. whipping cream, mayonnaise,
Jell-O)
• Suspension – a heterogeneous mixture of two or
more substances with larger-sized particles.
Usually unstable. (ex. clay in water, smoke in air)
Diffusion of Gases
Ionic compounds
Ionic compounds
Ionic compounds
Polar molecules
–
O
+
H
+
H
Ionic compounds
–
+
Na
+
Na
–
Cl
Cl
–
Cl
+
Na
–
+
Na
+
Na
–
Cl
–
Cl
Cl
+
Na
NaCl Dissolved in Water
–
O
+
+
H
H
Cl
–
NaCl Dissolved in Water
+
Na
NaCl Dissolved in Water
NaCl Dissolved in Water
Sucrose Dissolved in Water
Precipitate
Precipitate – A solid that comes out of the
solution.
Iron (II) hydroxide
benzoic acid
Precipitate
lead (II) nitrate
Concentrations
• Concentration – how much solute is dissolved
within a certain amount of solution.
• g solute/L solution
• ppm – parts per million (mass)
• ppb – parts per billion
• Molarity (M) – mol solute/L solution
• Molality – mol solute/kg solvent
• % composition = mass solute/mass total
Concentrations Examples
g solute
3.7 g NaCl
=
L solution
1 L solution
ppm – parts per million (mass)
25 g LiF
=
= 25 ppm (mass)
1,000,000 g solution
mol solute 3.0 mol MgCl2
Molarity (M) =
=
1 L solution
L solution
= 3.0 M MgCl2 solution
Concentrations Examples
Molality – mol solute/kg solvent
% composition = mass solute/mass total
Concentration Example #1
• If 12 moles of KCl are dissolved in a 3 L
solution with water, what is the molarity of
the KCl solution?
12 mol KCl
= 4 M KCl solution
3 L solution
Concentration Example #2
• How many moles of sodium chloride (NaCl)
are dissolved in 5 L of NaCl solution with a
concentration of 3M?
5 L solution 3 mol NaCl
x
= 15 mol NaCl
1
1 L solution
OR
x mol NaCl
3 mol NaCl
=
5 L solution
1 L solution
Solubility
• soluble – something that can dissolve into a
solution.
• insoluble – something that cannot dissolve
into a solution.
• saturated – no more solute can dissolve into
the solution.
• unsaturated – more solute can still dissolve
into the solution.
Solubility
• supersaturated – more than the normal
amount of solute is dissolved in the solution.
A slight change may force the excess solute to
precipitate out of solution.
Solubility
Graph
Solubility
Graph
Solubility
Graph
Electrical Conductivity
• Distilled water does not conduct electricity
• Electrolytes – dissolved salts or acids that
allow water to conduct electricity because of
positive or negative ions.
Diluting Solutions
• While the molarity (M) and the volume (V)
may change, the number of moles (M × V) will
not change.
M1 × V 1 = M 2 × V 2
before
after
Diluting Example #1
• 5.0 liters of a 3.0 M NaCl solution is diluted so
the volume of the solution is now 30 liters.
What is the molarity of the diluted solution?
M1 × V 1 = M 2 × V 2
(3.0 M) × (5.0 L) = M2 × (30 L)
15 = 30 M2
30
30
0.5 M = M2
Like Dissolves Like
• Polar molecules dissolve polar molecules.
Water, alcohols, vinegar
• Nonpolar molecules dissolve nonpolar
molecules.
 Fats, oils, gasoline
• Usefulness of soap in washing off greasy
hands comes from soap molecules having
both polar and nonpolar ends.
Factors that Affect Solubility
• Surface Area – Smaller particles have more
surface area than larger particles. Surface area
allows the solute to dissolve faster.
Factors that Affect Solubility
• Surface Area – Smaller particles have more
surface area than larger particles. Surface area
allows the solute to dissolve faster.
Factors that Affect Solubility
• Stirring – increases solute’s contact with low
concentration solvent. The solute dissolves
faster.
• Temperature – Higher temperatures usually
allow more solids to dissolve in liquids but
less gases.
• Pressure – Higher pressures usually allow
more gases to dissolve in liquids.
Gas Dissolved in Water
Concentration Effects
(aka Colligative Properties)
• Depressed Freezing Point (anti-freeze, salting
the roads and sidewalks in winter) – freezes at
a lower temperature because of the solute.
• Elevated Boiling Point (anti-boil radiator fluid)
– boils at a higher temperature because of the
solute.
Separations
• Decanting – carefully pouring the solution from a
container while leaving the precipitate.
• Centrifugation – spinning a suspension very fast
so the precipitate settles on the bottom.
• Filtration – using a filter to trap the precipitate
while the solution passes through.
• Evaporation – heating and evaporating out the
solvent so only the solute remains.
• Chromatography – Utilizing different substances’
varying attraction to certain materials so one
substance travels faster than the other.
• Distillation – Separating 2 liquids heating them
both and having them boil out at their different
boiling points.
Decanting
• Decanting – carefully pouring the solution
from a container while leaving the precipitate.
Centrifugation
• Centrifugation – spinning a suspension very
fast so the precipitate settles on the bottom.
Filtration
• Filtration – using a filter to trap the precipitate
while the solution passes through.
Evaporation
• Evaporation – heating and evaporating out
the solvent so only the solute remains.
Chromatography
• Chromatography – Utilizing different
substances’ varying attraction to certain
materials so one substance travels faster than
the other.
Distillation
• Distillation – Separating 2 liquids heating
them both and having them boil out at their
different boiling points.
Concentration Example #3
• Pure gold nuggets are very rare. Instead most
mining companies settle for rocks that contain
only small amount of gold. If a 1,000 g rock
contains 200 mg of gold, then what is the
concentration in parts per million of gold in the
rock?
200 g Au
200 mg Au
0.200 g Au 1,000
=
x
=
1,000 g rock 1,000 g rock 1,000 1,000,000 g rock
= 200 ppm Au (mass)
Concentration Example #3
• Pure gold nuggets are very rare. Instead most
mining companies settle for rocks that contain
only small amount of gold. If a 1,000 g rock
contains 200 mg of gold, then what is the
concentration in parts per million of gold in the
rock?
6
10
200 g Au
200 mg Au
1g
1,000
x
x 6 =
1,000 g rock 1,000 mg 10
1,000,000 g rock
1,000
= 200 ppm Au (mass)
Concentration Example #4
• 11.1 g of CaCl2 are dissolved within a 500 mL
solution with water. What is the molarity of
the CaCl2 solution?
11.1 g CaCl2
1 mol CaCl2 1,000 mL
x
x
=
500 mL solution 111 g CaCl2
1L
= 0.2 M CaCl2 solution
Carbonated Soda
Under High pressure
Under Normal Pressure
Save for Equilibrium Shifts Unit since technically there
is an unstable acid compound that CO2 forms in
solution.
H
He
Li Be B
C
N
O
F
Na Mg Al
Si
P
S
Cl Ar
K
Ca
Ne
Br Kr
I
Xe
H
He
Li Be B
C
N
O
F
Na Mg Al
Si
P
S
Cl Ar
K
Ca
Ne
Br Kr
I
Xe
Bad Example #X
• Carbon dioxide (CO2) is present in a mixture of
gases at STP with a concentration of 500 ppm. If
there are a 44.8 L of the gas mixture , how many
moles of carbon dioxide?
44.8 L mixture 1 mol mixture
500 mol CO2
x
x 6
1
22.4 L mixture 10 mol mixture
= 0.001 mol CO2
4 e– in valence shell
Solubility
Graph