Physical Properties of Solutions

Chapter 13

SolutionStoichiometry

12.1

A solution is a homogenous mixture of 2 or more substances

The solute is(are) the substance(s) present in the smaller amount(s)

The solvent is the substance present in the larger amount

An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity.

A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity.

nonelectrolyte weak electrolyte strong electrolyte4.1

A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.

An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature.

A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature.

Sodium acetate crystals rapidly form when a seed crystal isadded to a supersaturated solution of sodium acetate.

12.1

The solution Process

1. The ease of solution depends on two factors

a. the change in energy (enthalpy)

b. the change in disorder (Entropy)

2. The solution process is favored when there is a decrease in enthalpy an increase in entropy

9

How do we know ions areHow do we know ions arepresent in aqueouspresent in aqueoussolutions?solutions?

The solutionsThe solutions______ _______________ _______________ __________ ____

They are calledThey are calledELECTROLYTESELECTROLYTES

HClHCl, MgCl, MgCl22, and , and NaClNaCl are arestrong electrolytesstrong electrolytes..They dissociateThey dissociatecompletely (or nearly so)completely (or nearly so)into ions.into ions.

Aqueous SolutionsAqueous Solutions

10

AqueousAqueousSolutionsSolutions

Some compoundsSome compoundsdissolve in water butdissolve in water butdo not conductdo not conductelectricity. They areelectricity. They arecalled called nonelectrolytesnonelectrolytes..

Examples include:sugarethanolethylene glycol

Examples include:Examples include:sugarsugarethanolethanolethylene glycolethylene glycol

12

Electrolytes in the BodyElectrolytes in the Body

Carry messages toCarry messages to

and from the brainand from the brain

as electrical signalsas electrical signals

Maintain cellularMaintain cellular

function with thefunction with the

correctcorrect

concentrationsconcentrations

electrolyteselectrolytes

50-70 g sugar50-70 g sugarOne liter of warm waterOne liter of warm waterPinch of saltPinch of salt200ml of sugar free fruit200ml of sugar free fruit

squashsquashMix, cool and drinkMix, cool and drink

Make your ownMake your own

3. Heat of solution Hsolution

a. if a solution gets hotter as a substance dissolves - energy is being released

i. -Hsolution designates the release of energy

ii. The more negative the Hsolution, the more favorable the solution process

4. Main interactions that affect the solution process

strong solvent - solvent attractions does not favor solubility

weak solvent-solvent attractions favor solubility

weak solute - solute attractions favor solubility

5. three process

a. breaking apart the solute particles (endothermic)

b. breaking apart solvent solvent particles (endothermic)

c. interactions of solute and solvent particles (exothermic)

12.2

Three types of interactions in the solution process:• solvent-solvent interaction• solute-solute interaction• solvent-solute interaction

DHsoln = DH1 + DH2 + DH3

Requires heat Requires heat

Gives off heat

“like dissolves like”

Two substances with similar intermolecular forces are likely to be soluble in each other.

• non-polar molecules are soluble in non-polar solvents

CCl4 in C6H6

• polar molecules are soluble in polar solvents

C2H5OH in H2O

• ionic compounds are more soluble in polar solvents

NaCl in H2O or NH3 (l)

12.2

F. dissolution of solids in liquids

the process in which solvent molecules surround and interact with solute ions or molecules is called solvation

When the solvent is water - it is called hydration

G Dissolution of liquids in liquids (miscibility)

1. Miscibility - ability of one liquid to dissolve in another

miscible - mutually soluble in all proportions

Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner.

d+

d-

H2O 4.1

H factors that effect solubility

1. Types of solvents and solute

a. General rule - like dissolves like-polar dissolves polar - nonpolar dissolves nonpolar

b. nonpolar mixed with polar will be immiscible

2. surface area - cause more collisions of the solute and the solvent

3. temperature

a. in general - as temperature increase so does

solubility for solids

b. for gases - an increase in temperature causes a decrease in solubility

Concentration UnitsThe concentration of a solution is the amount of solute present in a given quantity of solvent or solution.

Percent by Mass

% by mass = x 100%mass of solutemass of solute + mass of solvent

= x 100%mass of solutemass of solution

12.3

Mole Fraction (X)

XA = moles of A

sum of moles of all components

Concentration Units Continued

M =moles of solute

liters of solution

Molarity (M)

Molality (m)

m =moles of solute

mass of solvent (kg)

12.3

What is the molarity of 200.0 g of H3PO4 in enough water to make 2.00 L

M = moles Liters

You must first find the number of moles of H3PO4

(200.0 g H3PO4)

(98.02 g H3PO4)

( 1 mole H3PO4) = 2.040 moles

2.00 L

= 1.02 M

Molarity continued

How many liters can be prepared of a 2.0 M solution of KOH if 400.0 g of KOH is available

Remember Molarity is = molesLiters

Change Molarity back into these units

2.0 M = 2.0 molesLiters

This gives us units that we can work with

Change grams to moles

400.0 g KOH( ) ( )56.01 g KOH

1 mole KOH= 7.142 moles KOH

7.142 Moles KOH( ) ( )2.0 Moles KOH

1 liter= 3.6 L

How many gram of NaOH are required to make 5.00 L of a 2.5 Molar solution

First change Molar into mole/liter

2.5 Molar = 2.5 moles liters

2.5 molesliter

( ) ( )( 5.00 L)1 mole NaOH

40.0 g NaOH = 500 g

Colloidsb. Colloids - particles that are intermediate in size.

i. Particles are on the order of 1 to 100 nm

ii. look cloudy

v. e.g. mayonnaise, gels, foams, smoke, fog, smog

iv. Tyndall Effect

iii. Brownian motion

Suspensionsa. Suspensions - large particles that will settle

if not agitated

i. Particles are on the order of 100 nm, which is about 1000 times bigger than atoms

Temperature and Solubility

Solid solubility and temperature

solubility increases with increasing temperature

solubility decreases with increasing temperature

12.4

Temperature and Solubility

Gas solubility and temperature

solubility usually decreases with

increasing temperature

12.4

Pressure and Solubility of Gases

12.5

The solubility of a gas in a liquid is proportional to the pressure of the gas over the solution (Henry’s law).

c = kP

c is the concentration (M) of the dissolved gas

P is the pressure of the gas over the solution

k is a constant (mol/L•atm) that depends onlyon temperature

low P

low c

high P

high c

4.5

Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution.

Dilution

Add Solvent

Moles of solutebefore dilution (i)

Moles of soluteafter dilution (f)=

MiVi MfVf=4.5

How would you prepare 60.0 mL of 0.2 MHNO3 from a stock solution of 4.00 M HNO3?

MiVi = MfVf

Mi = 4.00 Mf = 0.200 Vf = 0.06 L Vi = ? L

4.5

Vi =MfVf

Mi

=0.200 x 0.06

4.00= 0.003 L = 3 mL

3 mL of acid + 57 mL of water = 60 mL of solution

TitrationsIn a titration a solution of accurately known concentration is added gradually to another solution of unknown concentration until the chemical reaction between the two solutions is complete.

Equivalence point – the point at which the reaction is complete

Indicator – substance that changes color at (or near) the equivalence point

Slowly add baseto unknown acid

UNTIL

the indicatorchanges color

4.7

What volume of a 1.420 M NaOH solution isRequired to titrate 25.00 mL of a 4.50 M H2SO4 solution?

4.7

WRITE THE CHEMICAL EQUATION!

volume acid moles acid moles base volume base

H2SO4 + 2NaOH 2H2O + Na2SO4

4.50 mol H2SO4

1000 mL solnx

2 mol NaOH

1 mol H2SO4

x1000 ml soln

1.420 mol NaOHx25.00 mL = 158 mL

M

acid

rx

coef.

M

base

Fractional Distillation Apparatus

12.6

The Cleansing Action of Soap

12.8

Solution Stoichiometry

The concentration of a solution is the amount of solute present in a given quantity of solvent or solution.

M = molarity =moles of solute

liters of solution

What mass of KI is required to make 500. mL ofa 2.80 M KI solution?

volume KI moles KI grams KIM KI M KI

500. mL = 232 g KI166 g KI

1 mol KIx

2.80 mol KI

1 L solnx

1 L

1000 mLx

4.5