Solutions

1
Chapter 15

• Solutions

2
Obj. 1-2Vocabulary

• solution

homogenous mixture
smallest particles
no Tyndall effect
wont settle out
composed of solute and solvent
gets dissolved
does the dissolving
always more solvent than solute!

• name the solute/solvent in the following
  solutions

solute
solvent
salt
water
salt water
atmosphere
N2
other gases
brass
Cu
Zn
(Zn and Cu)
3
Obj. 1-2 cont

• solubility

the amount of solute that will dissolve in a
solvent at a given temperature.

• miscible

liquids that are capable of dissolving each
other. (alcohol and water)

• immiscible

liquids that are insoluble in each other
they dont mix. (oil and water)

• solvation

the process that occurs as an ionic solute
dissolves.
solute breaks apart (dissociates) into cation
()
and anion(-).
solvent particles surround individual ions
WILL NOT occur if ionic bonds are stronger
than their attraction to the solvent.
4
Obj. 1-2 cont

• hydration

solvation in which water is the solvent.
5
Obj. 3Solvation Rules

• in order for solvation to occur, a solute must be

broken apart and surrounded by solvent particles.

• use the rule like dissolves like to predict
  whether

solvation will occur.
starts w/ metal (cation)
polar (ionic) solvents dissolve polar solutes
non-polar (covalent) solvents dissolve
non-polar
solutes
starts w/ non-metal

• will solvation occur in the following
  examples?!?!

no
yes
NaCl and H2O
P2O5 and H2O
no
yes
KCl and C6H6
CCl4 and C6H6
6
Obj. 4-5Solvation of Solids and Gases

• In general, chemical rxns. are more likely to
  occur if

they are exothermic and increasing in entropy.

• an exothermic reaction releases thermal energy
  to the

environment. (chemical bonds are created)

• an endothermic reaction absorbs thermal energy
  from

the environment. (chemical bonds are broken)

• entropy (?S) is a measure of disorder of a
  system.

All natural processes tend to increase in
entropy.
high entropy more disorder
Ex
solid gas
Rxns. w/ more products than reactants!
low ?S
high ?S
high ?S
7
Obj. 4-5 cont

• The problem with solids

• the solvation of solids is an endothermic process

(dissociation into ions requires a lot of broken
bonds!)

• The solution

• Must contain huge amounts of entropy in order to

occur spontaneously.
one salt crystal dissociates into millions of
ions!
8
Obj. 4-5 cont

• The problem with gases

• the solvation of a gas requires a decrease in
  entropy

(liquids have less entropy than gases)

• The solution

• Reactions must be largely exothermic in order to

occur spontaneously.
9
Obj. 6How P T Affect Solvation

• IN GENERALsolubility rate of a solid in a liquid

increases with
increased temps.
(sugar is more soluble in hot tea than iced tea)

• IN GENERALsolubility rate of a gas in a liquid

increases with
decreased temps.
(warm soft drinks quickly go flat)
increased pressure
(CO2 comes out of solution when a new coke is
opened)
10
Obj. 7Factors Affecting Solubility

• Important factors affecting solubility rates

particle size/surface area
(smaller more soluble)
agitation/stirring
(more agitation more soluble)
temperature
(depends on solute)
gases like cold
solids like hot
11
Obj. 10Dilute vs. Concentrated

• concentrated solutions contain a high amount of

solute.
strong

• diluted solutions contain a low amount of solute.

weak

• These terms are not very helpful when describing
  solution concentration b/c they are completely
  relative.

• 1 gram of solute compared to 10 grams dilute

• 1 gram of solute compared to 0.1 grams
  concentrated

12
Obj. 11Types of Solutions

• unsaturated solutions contain a less solute than
  they

are capable of dissolving at a given T and P.
can hold morenot full yet!

• saturated solutions contain the max. amount of
  solute

that they are capable of dissolving at a given T
and P.
equilibrium exists b/n dissolved and
undissolved solute.
completely full, cant hold any more!

• supersaturated solutions contain more solute
  (dissolved)

than it is supposed to hold at a given T and P.
must heat solution up to allow more solute to
dissolve
then let it cool down very slowly, undisturbed.
13
Obj. 11 cont

• a solubility curve shows saturated solutions of
  given

substances at given temps.
any coordinate below this curve unsaturated
any coordinate above this curve
supersaturated
14
Obj. 11 cont

• Which substance is most soluble at 40C?

NaNO3
50 grams

• How many grams of NH4Cl will dissolve at 50C?

KNO3 and

• What two substances have the same solubility at
  24C?

Yb2(SO4)3

• If you place 70 grams of KBr into 100g of water
  at 60C, what

unsaturated
type of solution have you made?

• How many grams of NaNO3 will dissolve in 300.0g
  of water at

240 grams
(80 x 3)
10.0C?
15
Obj. 8Precipitates

• precipitate

an insoluble solid that will separate from
a solution during a reaction (double
displacement).
using solubility rules, we can predict
precipitates.
Compound Solubility Exceptions
Salts of group 1A and ammonia (NH3) Soluble (aq) Some lithium compounds
Ethanoates, nitrates, chlorates, and perchlorates Soluble (aq) Few Exceptions
Sulfates (SO4) Soluble (aq) Compounds of Pb, Ag, Hg, Ba, Sr, and Ca
Chlorides, Bromides, and Iodides Soluble (aq) Compounds of Ag and some of Hg and Pb
Sulfides and Hydroxides Insoluble (s) Group 1A compounds. Compounds of Ba, Sr, and Ca (slightly)
Carbonates, Phosphates, and Sulfites Insoluble (s) Group 1A and ammonia (NH3) compounds
16
Obj. 8 cont
Compound Solubility Exceptions
Salts of group 1A and ammonia (NH3) Soluble (aq) Some lithium compounds
Ethanoates, nitrates, chlorates, and perchlorates Soluble (aq) Few Exceptions
Sulfates (SO4) Soluble (aq) Compounds of Pb, Ag, Hg, Ba, Sr, and Ca
Chlorides, Bromides, and Iodides Soluble (aq) Compounds of Ag and some of Hg and Pb
Sulfides and Hydroxides Insoluble (s) Group 1A compounds. Compounds of Ba, Sr, and Ca (slightly)
Carbonates, Phosphates, and Sulfites Insoluble (s) Group 1A and ammonia (NH3) compounds

• Predict the precipitate

precipitate
1
-1
1
-1
LiNO3
AgI
LiI (aq) AgNO3 (aq)
(s)
(aq)
precipitate
1
-1
-2
3
6NaOH (aq) Cr2(SO4)3 (aq)
3Na2SO4
2Cr(OH)3
(aq)
(s)
17
Obj. 9Net Ionic Equations

• a net ionic equation shows the chemical change
  in a

solution (formation of precipitate).
all soluble (aq) compounds are separated into
ions.
insoluble (s) compounds are written as
compounds.

• To write

write the complete ionic equation.

• separate (aq) compounds.

• leave (s) compounds intact.

cross out any spectator ions

• ions that appear on both sides of equation.

18
Obj. 9 cont

• Ex

LiI (aq) AgNO3 (aq)
LiNO3 (aq)
AgI (s)

• write complete ionic equation

Li1
I-1
Ag1
NO3-1
Li1
NO3-1
AgI (s)

• cross out spectator ions

• what is left is the net ionic equation!

I-1
Ag1
AgI (s)

• Ex

6NaOH (aq) Cr2(SO4)3 (aq) 3Na2SO4
(aq)
2Cr(OH)3 (s)
6Na1
6OH-1
2Cr3
2Cr(OH)3 (s)
3SO4-2
6Na1
3SO4-2
6OH-1
2Cr3
2Cr(OH)3 (s)
19
Obj. 12-13Solution Calculations

• we said that dilute and concentrated are very

general terms for solution concentration.

• Molarity indicates how many moles of solute are

dissolved in one liter of solution.
moles
molarity
units M
Liters

• Ex

What is the molarity of a salt water solution
containing
9.0 moles of salt dissolved in 3.0 liters of
solution?
9.0 moles

3.0 M
3.0 liters
20
Obj. 12-13 cont

• Ex

23
35
What is the molarity of 174 grams of NaCl
dissolved in
500.0 mL of solution?
moles
molarity
Liters
174 grams
1 mole
1000 mL

500.0 mL
1 liter
58 grams NaCl
6.00 M
21
Obj. 12-13 cont

• Molality indicates how many moles of solute are

dissolved in one kilogram of solvent.
moles
molality
units m
Kg

• Ex

59
160
What is the molality of 199 grams of NiBr2 in
500.0
grams of water?
199 grams NiBr2
1 mole
1000 grams

500.0 grams
219 grams NiBr2
1 Kg
1.82 m
22
Obj. 12-13 cont

• Other types of solution concentration include

part
mass of solute or solvent
mass

x
100
whole
mass of solution
part (solute)

• Ex

What is the by mass of 62.0 grams of KCl
dissolved in
475 grams of water?
solvent
part
mass
whole
whole solution
solute solvent!
62.0 475 537 grams of solution
62.0
mass

x
100
11.5
537
23
Obj. 12-13 cont
part (solute)
whole (solution)

• Ex

How many grams of KOH are required to prepare
450.0
grams of a 30.0 solution?

part
x
mass
whole
x
whole
part x whole
whole

KOH
0.300
x
450.0
135 g
pph
parts per hundred
ppt
parts per thousand
parts per million
ppm
24
Obj. 12-13 cont

• Dilution calculations

a dilution a solution is made less
concentrated
(weaker) by adding more solvent.

• changes concentration (molarity).

• changes volume of solution.

M1V1 M2V2
initial molarity
final molarity
initial volume
final volume
25
Obj. 12-13 cont
M1

• Ex

V1

• How many liters of a 12M solution are needed to
  create

2.0 liters of a 4.0M solution?
M1V1 M2V2
M2
V2
8.0
12
X

12
X
2.0
(4.0)

0.67 liters
X
12
12
V1

• Ex

M1

• What is the molarity of 1.5 liters of solution
  made from

600.0 mL of 10.0M NaOH?
M2
V2
6.0
1.5
X

4.0M
1.5
X
0.6
(10.0)

X
1.5
1.5
26
Obj. 12-13 cont

• Some dilution problems may contain
  concentrations

instead of molarity
you do NOT have to put in decimal formjust
be consistent!
1

• Ex

mass1

• How many grams of a 25.0 solution of a KCl are
  needed to

prepare 85.0 grams of a 40.0 solution?
2
mass2
1mass1 2mass2
25
X
3400
(40)
25
X
85

136 grams

X
25
25
27
Obj. 14Colligative Properties

• Colligative properites are properties of
  solutions that are

affected only by the of particles in the
solution.

• NOT affected by the type of particle!!!

• Ex

vapor pressure (VP)
freezing point (FP)
boiling point (BP)
28
Obj. 15Effect of Solutes on Vapor Pressure

• Vapor pressure (VP) is the P exerted at the
  surface of a

liquid by particles trying to escape the liquid.
29
Obj. 15 cont

• adding a nonvolatile solute to a solvent will
  cause the VP of

the solvent to decrease.
solute particles replace some solvent
particles at the
surface of the solution.
less solvent particles on surface less
evaporation
lower VP!
30
Obj. 16 and 18How Solutes Affect BP and FP

• Boiling pt. (BP) is temp. at which the VP of the
  liquid

atmospheric pressure.
adding solute lowers VP of solvent
must add more KE (heat) to equalize the
pressures
solutes RAISE the BP of solutions!
(i.e. we add salt before we boil water)
pure water
salt water
31
Obj. 16 and 18 cont

• Freezing pt. (FP) is temp. at which liquid turns
  into a solid.

enough KE is lost (removal of heat) that
molecules stop
moving around and lock into place.
adding solute lowers VP of solvent
even more KE (heat) must be lost to lock
molecules into
place.
solutes LOWER the FP of solutions!
(i.e. we add salt to icy roadssalt is used in
making ice cream )
32
Obj. 16 and 18 cont

• Ionic solutes lower the VP of solvents more than
  molecular

solutes!
ionic solutes dissociate (break up into ions)
in solvents.

• AlCl3 dissociates into 4 separate ions (1 Al3
  and 3 Cl-1)

molecular solutes stay intact in solvents.

• glucose (C6H12O6) breaks into separate units of
  C6H12O6

NOT Cs, Hs and Os!
33
Obj. 17BP and FP Calculations

• solutes raise (elevate) the BP of solvents.

• to calculate how high the BP is elevated

BP elevation ?TBP
m(KBP) normal BP
given except
BP constant
molality
water 100C
given

• solutes lower (depress) the FP of solvents.

• to calculate how low the FP is depressed

FP depression ?TFP
normal FP - m(KFP)
given except
FP constant
molality
water 0C
given
ionic solutes affect molality!!!
CaCl2 dissociates into 3 ions, so multiply m by 3!
Round all temps. to the hundredths place!
34
Obj. 17 cont

• Ex

If 52.34 grams of NiBr2 dissolve in 392.0 grams
of water, what is the BP of the resulting
solution?
BP m(KBP) normal BP
52.34 g NiBr2
1 mole
1000 g
x 3
1.829 m
0.6097 m

219 g NiBr2
392.0 g water
1 Kg
(ions)
0.936
(0.512)
100C
100.94C
BP
1.829
35
Obj. 17 cont

• Ex

If 95.67 grams of CCl4 dissolve in 981.0 grams of
benzene, what is the FP of the resulting
solution? (FP of Benzene 5.53C)
FP normal FP - m(KFP)
molecular, so dont multiply by anything!
95.67 g CCl4
1 mole
1000 g
0.6416 m

152 g CCl4
981 g benzene
1 Kg
3.285
2.25C
FP
5.53C
(5.12)
- 0.6416