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Chapter 15. Solutions. Obj. 1-2…Vocabulary. solution :. homogenous mixture. ~ smallest particles. ~ no Tyndall effect. ~ won’t settle out. ~ composed of solute and solvent. does the dissolving. gets dissolved. ** always more solvent than solute! **.

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Chapter 15

Chapter 15

Solutions


Obj. 1-2…Vocabulary

  • solution:

homogenous mixture

~ smallest particles

~ no Tyndall effect

~ won’t settle out

~ composed of solute and solvent

does the dissolving

gets dissolved

** always more solvent than solute! **

  • name the solute/solvent in the following solutions…

solvent

solute

salt

water

salt water

atmosphere

other gases

N2

brass

Zn

Cu

(Zn and Cu)


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 ‘don’t 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.


Obj. 1-2 cont…

  • hydration:

solvation in which water is the solvent.


Obj. 3…Solvation 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

~ P2O5 and H2O

~ NaCl and H2O

no

yes

~ CCl4 and C6H6

~ KCl and C6H6


Obj. 4-5…Solvation of Solids and Gases

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

they are exothermicand 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(ΔS) 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 ΔS

high ΔS

high ΔS


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!


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.


Obj. 6…How P & T Affect Solvation

  • IN GENERAL…solubility rate of a solid in a liquid

increases with…

~ increased temps.

(sugar is more soluble in hot tea than iced tea)

  • IN GENERAL…solubility 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)


Obj. 7…Factors 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


Obj. 10…Dilute 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


Obj. 11…Types of Solutions

  • unsaturated solutions contain a less solute than they

are capable of dissolving at a given T and P.

~ can hold more…not 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, can’t 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.


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


Obj. 11 cont…

NaNO3

  • Which substance is most soluble at 40°C?

~ 50 grams

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

KNO3 and

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

Yb2(SO4)3

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

10.0°C?


Obj. 8…Precipitates

  • precipitate:

an insoluble solid that will separate from

a solution during a reaction (double displacement).

~ using solubility rules, we can predict precipitates.


Obj. 8 cont…

  • Predict the precipitate…

*precipitate*

+1

-1

+1

-1

LiNO3+

AgI

LiI (aq) + AgNO3(aq)

(s)

(aq)

*precipitate*

+1

-1

-2

+3

NaOH (aq) + Cr2(SO4)3(aq)

Na2SO4+

Cr(OH)3

(aq)

(s)


Obj. 9…Net Ionic Equations

  • a net ionic equationshows 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.


Obj. 9 cont…

  • Ex…

LiI (aq) + AgNO3(aq) LiNO3(aq) +

AgI (s)

  • write complete ionic equation…

Li+1 +

I-1 +

Ag+1 +

AgI (s)

NO3-1

Li+1 +

NO3-1 +

  • cross out spectator ions…

  • what is left is the net ionic equation!

I-1 +

Ag+1

AgI (s)

  • Ex…

NaOH (aq) + Cr2(SO4)3(aq) Na2SO4(aq) +

Cr(OH)3(s)

Na+1 +

OH-1 +

Cr+3 +

Cr(OH)3(s)

SO4-2

Na+1 +

SO4-2 +

OH-1 +

Cr+3

Cr(OH)3(s)


Obj. 12-13…Solution Calculations

  • we said that ‘dilute’ and ‘concentrated’ are very

general terms for solution concentration.

  • Molarityindicates 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


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


Obj. 12-13 cont…

  • Molalityindicates 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


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 = 537grams of solution

62.0

% mass =

=

x

100

11.5%

537


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 =

x

whole

whole

part = % x whole

whole

=

x

KOH =

0.300

450.0

135 g

~ pph =

parts per hundred

~ ppt =

parts per thousand

parts per million

~ ppm =


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


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

=

(4.0)

2.0

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

=

(10.0)

X=

0.6

1.5

1.5


Obj. 12-13 cont…

  • Some dilution problems may contain % concentrations

instead of molarity…

~ you do NOT have to put % in decimal form…just

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


Obj. 14…Colligative 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)


Obj. 15…Effect 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.


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!


Obj. 16 and 18…How 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


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 roads…salt is used in making ice cream )


= Al+3

= Cl-1

glucose

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 Al+3 and 3 Cl-1)

~ molecular solutes stay intact in solvents.

  • glucose (C6H12O6) breaks into separate units of C6H12O6…

NOT C’s, H’s and O’s!


Obj. 17…BP and FP Calculations

  • solutes raise (elevate) the BP of solvents.

  • to calculate how high the BP is elevated…

BP elevation = ΔTBP

= m(KBP) + normal BP

*given except…*

BP constant

molality

*water = 100°C*

*given*

  • solutes lower (depress) the FP of solvents.

  • to calculate how low the FP is depressed…

FP depression = ΔTFP

= normal FP-m(KFP)

*given except…*

FP constant

molality

*water = 0°C*

*given*

** ionic solutes affect molality!!! **

CaCl2 dissociates into 3 ions, so multiply m by 3!

** Round all temps. to the hundredths place! **


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

x3=

1.829 m

0.6097 m

=

219 g NiBr2

392.0 g water

1 Kg

(ions)

0.936

(0.512)

+ 100°C =

100.94°C

BP =

1.829


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 = 5.53°C)

FP = normal FP-m(KFP)

** molecular, so don’t multiply by anything!

95.67 g CCl4

1 mole

1000 g

0.6416 m

=

152 g CCl4

981 g benzene

1 Kg

3.285

2.25°C

FP =

5.53°C

- 0.6416

(5.12) =


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