Dilute vs. Concentrated

• Concentrated solutionsConcentrated solutions contain a high amount of solute.

• 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 =• 1 gram of solute compared to 0.1 grams =

dilute

concentrated

Types of Solutions• Unsaturated solutionsUnsaturated solutions contain a less solute than

they are capable of dissolving at a given T and P.

~ can hold more…not full yet!

• Saturated solutionsSaturated 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 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.

Solution Calculations

•we said that ‘dilute’ and ‘concentrated’ are very general terms for solution concentration.

• MolarityMolarity indicates how many moles of solute are dissolved in one liter of solution.

moles Liters

~ units = M

• 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 liters =

3.0 3.0 MM

~ molarity =

What is the molarity of 174 grams of NaCl dissolved in 500.0 mL of solution?

• 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

• 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

• Ex…

How many grams of KOH are required to prepare 450.0 grams 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 gg

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

(weaker) by adding more solvent.

MM11VV11 = M = M22VV22

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 2.0 liters of a 4.0M solution?

MM11VV11 = M = M22VV22

M1 V1

V2 M2

12

X

2.0 (4.0) =

0.67 0.67 liters liters

12

X

=

8.0 12

12

X=

• Ex…• What is the molarity of 1.5 liters of solution made

from 600.0 mL of 10.0M NaOH?

V1 M1

V2 M2

1.5

X

0.6000 (10.0)

=

1.5 X

=

6.00 1.5

1.5

4.0M4.0M X=

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**

NaOH (aq) + Cr2(SO4)3 (aq) NaNa22SOSO44 +

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

*precipitate**precipitate*

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

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

Electrolytes vs. Non-Electrolytes

Electrolytes: dissociate in water readily and conduct an electric current. Any ionic compounds, some covalent

compounds

Non-electrolytes: dissolve in water, but don’t dissociate or conduct an electric current. All sugars and other covalent compounds

Colligative Properties

• Colligative propertiesColligative properties 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)

Effect of Solutes on Vapor Pressure

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

• 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!

How Solutes Affect BP and FP

• Boiling Point (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

• Freezing Point (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 )

•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!

glucose

= Al+3

= Cl-1