Chapter 15 Solutions. Obj. 1-2…Vocabulary solution : solution : homogenous mixture ~ smallest particles ~ no Tyndall effect ~ won’t settle out solutesolvent

Chapter 15Chapter 15SolutionsSolutions

Obj. 1-2…VocabularyObj. 1-2…Vocabulary• solutionsolution:: homogenous

mixture ~ smallest particles ~ no Tyndall effect ~ won’t settle out ~ composed of solutesolute and solventsolvent

gets dissolved

does the dissolving ** always more solvent than solute!

**• name the solute/solvent in the following solutions…

salt water

solute solvent

saltsalt waterwater

atmosphere NN22other gasesother gases

brass (Zn and

Cu)

CuCuZnZn

Obj. 1-2 cont…Obj. 1-2 cont…• solubilitysolubility:: the amount of solute that will dissolve

in asolvent at a given temperature.• misciblemiscible:: liquids that are capable of dissolving

eachother. (alcohol and water)• immiscibleimmiscible:: liquids that are insoluble in each

other…they ‘don’t mix’. (oil and water)• solvationsolvation:: the process that occurs as an ionic

solutedissolves. ~ solute breaks apart (dissociatesdissociates) into cation (+) ~ solvent particles surround individual ions

~ WILL NOT occur if ionic bonds are strongerthan their attraction to the solvent.

and anion(-).

Obj. 1-2 cont…Obj. 1-2 cont…

• hydrationhydration:: solvation in which water is the solvent.

Obj. 3…Solvation RulesObj. 3…Solvation Rules• in order for solvation to occur, a solute must bebroken apart and surrounded by solvent particles.

• use the rule ‘like dissolves like’ to predict whethersolvation will occur.

~ polar (ionic) solvents dissolve polar solutes

~ non-polar (covalent) solvents dissolve non-polarsolutes

starts w/ metal (cation)starts w/ metal (cation)

starts w/ non-metalstarts w/ non-metal

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

~ NaCl and H2O

yesyes

~ KCl and C6H6 nono

~ P2O5 and H2O

nono

~ CCl4 and C6H6

yesyes

Obj. 4-5…Solvation of Solids Obj. 4-5…Solvation of Solids and Gasesand Gases

• In general, chemical rxns. are more likely to occur ifthey are exothermic and increasing in entropy.

• an exothermicexothermic reaction releases thermal energy to the environment.

• an endothermic endothermic reaction absorbs thermal energy fromthe environment.

• entropyentropy ((ΔΔS)S) is a measure of disorder of a system.All natural processes tend to increase in entropy.

~ high entropy = more disorderEx…

solid gaslow low ΔΔSS high high ΔΔSS

Rxns. w/ more products than reactants! high high ΔΔSS


• the solvation of solids is an endothermic process

• Must contain huge amounts of entropy in order tooccur spontaneously.

dissociation (seperation into ions) requires energy!

~ one salt crystal dissociates into millions of ions!

• The problem with solids…

• The solution…


• the solvation of a gas requires a decrease in entropy

• Reactions must be largely exothermic in order tooccur spontaneously.

(liquids have less entropy than gases)

• The problem with gases…

• The solution…

Obj. 6…How Pressure & Temperature Affect Obj. 6…How Pressure & Temperature Affect SolvationSolvation

• IN GENERAL…solubility rate of

solid in a liquid:

temp ↑ causes solubility ↑

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

• IN GENERAL…solubility rate of a

•gas in a liquid:

warm soft drinks quickly go ‘flat’

CO2 forced into solution in an unopened soda – what happens when it is opened?

temp ↑ causes solubility ↓

pressure ↑ causes solubility ↑

Obj. 7…Factors Affecting Obj. 7…Factors Affecting SolubilitySolubility

• Important factors affecting solubility rates…

~ particle size/surface area

(smaller = more soluble)

~ agitation/stirring(more agitation = more soluble)

~ temperature(depends on solute)

solids like hot gases like cold

Obj. 10…Dilute vs. Obj. 10…Dilute vs. ConcentratedConcentrated

• concentrated solutionsconcentrated solutions contain a high amount ofsolute.

• diluted solutionsdiluted solutions contain a low amount of solute.

~ ‘strong’

~ ‘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 SolutionsObj. 11…Types of Solutions• unsaturated solutionsunsaturated solutions contain a less solute than theyare capable of dissolving at a given T and P.

~ can hold more…not full yet!

• saturated solutionssaturated solutions contain the max. amount of solutethat 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 solutionssupersaturated 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…Obj. 11 cont…

• a solubility curve shows saturated solutions of givensubstances at given temps.

~ any coordinate below this curve = unsaturated ~ any coordinate above this curve = supersaturated


• Which substance is most soluble at 40°C?• How many grams of NH4Cl will dissolve at 50°C?

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

• If you place 70 grams of KBr into 100g of water at 60°C, whattype of solution have you made?

• How many grams of NaNO3 will dissolve in 300.0g of water at 10.0°C?

NaNONaNO33

~ 50 ~ 50 gramsgramsKNOKNO3 3

andand YbYb22(SO(SO44))

33unsaturatedunsaturated

~ 240 ~ 240 gramsgrams

(80 x 3)(80 x 3)

Obj. 8…PrecipitatesObj. 8…Precipitates• precipitateprecipitate:: an insolubleinsoluble solid that will separate

from a solution during a reaction (double displacement). ~ using solubility rules, we can predict precipitates.

Compound Solubility ExceptionsSalts 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…

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

LiI (aq) + AgNO3 (aq) LiNOLiNO33 +

AgIAgI(aq)(aq) (s)(s)

*precipitate*precipitate**

6NaOH (aq) + Cr2(SO4)3 (aq) 3Na3Na22SOSO44 +

2Cr(OH)2Cr(OH)33(aq)(aq) (s(s))

*precipitate**precipitate*

+1+1 -1-1 +1+1 -1-1

+1+1 -1-1 +3+3 -2-2

Obj. 9…Net Ionic EquationsObj. 9…Net Ionic Equations

• a net ionic equationnet ionic equation shows the chemical change in a

~ 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.

solution (formation of precipitate).

~ cross out any spectator ions… ions that appear on both sides of

equation.

Obj. 9 cont…Obj. 9 cont…• Ex…

Li+1 +

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

I-1 + Ag+1 +

NO3-1 Li+1 + NO3

-1 +

• write complete ionic equation…

AgI (s)

• cross out spectator ions…• what is left is the net ionic equation!

I-1 + Ag+1 AgI (s)

AgI (s)

• Ex… 6NaOH (aq) + Cr2(SO4)3 (aq) 3Na2SO4 (aq)+2Cr(OH)3 (s)

6Na+1

+ 6OH-1+2Cr+3+

3SO4

-2 6Na+1+

3SO4-2+2Cr(OH)3 (s)

6OH-1

+2Cr+3

2Cr(OH)3 (s)

Obj. 12-13…Solution Obj. 12-13…Solution CalculationsCalculations

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

• MolarityMolarity indicates how many moles of solute are

~ molarity =

general terms for solution concentration.

dissolved in one liter of solution.

moles Liters

~ units = M

• Ex…

What is the molarity of a salt water solution containing9.0 moles of salt dissolved in 3.0 liters of solution?

9.0 moles 3.0 liters

=

3.0 3.0 M M


What is the molarity of 174 grams of NaCl dissolved in

• Ex…

~ molarity =

moles Liters

23 35

174 grams 500.0 mL 58 grams

NaCl

1 mole

1000 mL 1 liter

=

6.00 M 6.00 M

500.0 mL of solution?

Obj. 12-13 cont…Obj. 12-13 cont…• MolalityMolality indicates how many moles of solute aredissolved in one kilogram of solvent.

~ molality =

moles Kg

~ units = m

• Ex…

What is the molality of 199 grams of NiBr2 in 500.0grams of water?

199 grams NiBr2 500.0 grams

219 grams NiBr2 1 mole

1000 grams 1 Kg

=

1.82 m 1.82 m

59 160

• Other types of solution concentration include…


~ % mass% mass =

part whole

=

mass of solute or solvent mass of

solution

100

x

• Ex…

What is the % by mass of 62.0 grams of KCl dissolved in 475 grams of water?

solvent

part (solute)

% mass = part whole

% mass =

62.0 537

=

11.5% 11.5%

** whole = solution…solute + solvent!

62.0 + 475 = 537537 grams of solution

100

x

Obj. 12-13 cont…Obj. 12-13 cont…• Ex…

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

whole (solution)

%

part (solute)

% mass = part whole

whole xwhole x part = % x whole

KOH = 0.300

x 450.0

=

135 135 g g

~ pphpph = parts per hundred

~ pptppt = parts per thousand

~ ppmppm = parts per million

• Dilution Dilution calculationscalculations…… ~ a dilution = a solution is made less concentrated

MM11VV11 = M = M22VV22


(weaker) by adding more solvent.

changes concentration (molarity).

changes volume of solution.

initial molarity initial volume

final molarity

final volume

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

M1V1 = M2V2


2.0 liters of a 4.0M solution?

M1 V1

V2 M2

12

X

2.0 (4.0) =

0.67 liters 0.67 liters 12

X

=

8.0 12

12

X=

• Ex…•What is the molarity of 1.5 liters of solution made from600.0 mL of 10.0M NaOH?

V1 M1

V2 M2

1.5

X

0.6 (10.0)

=

1.5 X

=

6.0 1.5

1.5

4.0M4.0M X=

Obj. 12-13 cont…Obj. 12-13 cont…•Some dilution problems may contain % concentrations instead of molarity…

~ you do NOT have to put % in decimal form…justbe consistent!

• Ex…•How many grams of a 25.0% solution of a KCl are needed toprepare 85.0 grams of a 40.0% solution?

%1mass1 = %2mass2

mass1 %1

mass2 %2

25

X

85 (40) =

136 grams 136 grams 25

X

=

3400 25

25

X=

Obj. 14…Colligative Obj. 14…Colligative PropertiesProperties

•Colligative properitesColligative properites are properties of solutions that areaffected 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 Obj. 15…Effect of Solutes on Vapor PressureVapor Pressure

•Vapor pressure (VP)Vapor pressure (VP) is the P exerted at the surface of aliquid by particles trying to escape the liquid.

Obj. 15 cont…Obj. 15 cont…•adding a nonvolatile solute to a solvent will cause the VP of

~ solute particles replace some solvent particles at the surface of the solution.

the solvent to decrease.

~ less solvent particles on surface = less evaporation =lower VP!

Obj. 16 and 18…How Solutes Obj. 16 and 18…How Solutes Affect BP and FPAffect 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…Obj. 16 and 18 cont…•Freezing pt. (FP) is temp. at which liquid turns into a solid.

~ adding solute lowers VP of solvent

~ even more KE (heat) must be lost to lock molecules into

** solutes LOWER the FP of solutions!(i.e. we add salt to icy roads…salt is used in making ice cream )

~ enough KE is lost (removal of heat) that molecules stopmoving around and lock into place.

place.

Obj. 16 and 18 cont…Obj. 16 and 18 cont…•Ionic solutes lower the VP of solvents more than molecularsolutes!

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

~ molecular solutes stay intact in solvents.

AlCl3 dissociates into 4 separate ions (1 Al+3 and 3 Cl-1)

glucose (C6H12O6) breaks into separate units of C6H12O6…NOT C’s, H’s and O’s!

glucose

= Al+3

= Cl-1

Obj. 17…BP and FP Obj. 17…BP and FP CalculationsCalculations

•solutes raise (elevate) the BP of solvents.

•to calculate how high the BP is elevated…

BP elevationBP elevation = ΔΔTTBPBP= mm(K(KBPBP) + normal ) + normal BPBP

molality BP constant

*given*

*given except…* *water = 100°C*•solutes lower (depress) the FP of solvents.

•to calculate how low the FP is depressed…

FP depressionFP depression = ΔΔTTFPFP= normal FPnormal FP -- mm(K(KFPFP))

molality FP constant

*given*

*given except…* *water = 0°C*

** ionic solutes affect molality!!! ** ionic solutes affect molality!!! ****CaCl2 dissociates into 3 ions, so multiply m by

3!** Round all ** Round all tempstemps. to the hundredths place! . to the hundredths place! ****


• Ex…If 52.34 grams of NiBr2 dissolve in 392.0 grams of water, what is the BP of the resulting solution?

BP = BP = mm(K(KBPBP) + normal ) + normal BPBP 52.34 g

NiBr2 392.0 g water 219 g NiBr2 1 mole 1000

g 1 Kg = 0.6097

m x 3 =

1.829 m(ions)

BP = 1.829

(0.512)

+ 100°C = 100.94°100.94°C C

0.936


• 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 FPFP = normal FP -- mm(K(KFPFP))

95.67 g CCl4

981 g benzene 152 g CCl4 1 mole 1000

g 1 Kg = 0.6416

m

FP = 5.53°C (5.12) =

- 0.6416

2.25°C 2.25°C

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

3.285

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Chapter 15 Solutions. Obj. 1-2…Vocabulary solution : solution : homogenous mixture ~ smallest particles ~ no Tyndall effect ~ won’t settle out solutesolvent