SolutionsSolutionsRead Read

chapter chapter 1212

What determines What determines solubility?solubility? TemperatureTemperature

Pressure (when a gas is Pressure (when a gas is involved)involved)

Nature of the particles – Nature of the particles – – ““Like dissolves like”Like dissolves like”

Aqueous SolutionsAqueous Solutions

Water is a “polar” molecule.Water is a “polar” molecule.– The O in the molecule has a partial The O in the molecule has a partial

negative chargenegative charge– The H’s have a partial positive charge.The H’s have a partial positive charge.

O

H

H

Aqueous SolutionsAqueous Solutions

Water solvates (surrounds and Water solvates (surrounds and stabilizes) the ions.stabilizes) the ions.

– H’s (H’s (++) interact with the ) interact with the negatively charged anionsnegatively charged anions

– O (O (--) interacts with the ) interacts with the positively charged cationspositively charged cations

Aqueous SolutionsAqueous Solutions

- +

Solvation of anion Solvation of cation

http://www.mhhe.com/physsci/chhttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/emistry/essentialchemistry/flash/molvie1.swfmolvie1.swf

Henry’s LawHenry’s Law

The solubility of a gas in a The solubility of a gas in a liquid is directly proportional liquid is directly proportional to the pressure of the gas to the pressure of the gas above the liquid. (at above the liquid. (at constant temp.)constant temp.)

SS11 S S22

PP11 = = P P22

Solubility is defined Solubility is defined as grams per liter.as grams per liter.

(g/L)(g/L)

Example-Example-

If 0.85 g of gas at 4.0 atm If 0.85 g of gas at 4.0 atm of pressure dissolves in 1.0L of pressure dissolves in 1.0L of water at 25of water at 25°°C, how much C, how much will dissolve in 1.0L of water will dissolve in 1.0L of water at 1.2 atm of pressure and at 1.2 atm of pressure and the same temperature?the same temperature?

Units of Concentration:Units of Concentration:

1.1. Percent by MassPercent by Mass

% =% = mass masssolute solute

x 100x 100

massmasssolutionsolution

Example:Example:

What is the percent by What is the percent by mass of NaHCOmass of NaHCO33 in a in a solution containing 20g solution containing 20g NaHCONaHCO33 in 600g H in 600g H22O?O?

You have 1500. g of a bleach You have 1500. g of a bleach solution. The percent by solution. The percent by mass of the solute sodium mass of the solute sodium hypochlorite, NaOCl, is hypochlorite, NaOCl, is 3.62%. How many grams of 3.62%. How many grams of NaOCl are in the solution?NaOCl are in the solution?

How many grams of solvent How many grams of solvent were present?were present?

1a. Percent by volume1a. Percent by volume

% =% = volume volumesolute solute

X 100X 100

volumevolumesolutionsolution

Example-Example-

What is the percent by What is the percent by volume of ethanol in a volume of ethanol in a solution that contains 35mL solution that contains 35mL of ethanol dissolved in 115 of ethanol dissolved in 115 mL of water?mL of water?

2. Molarity2. Molarity

MM = = mols mols solutesolute

litersliterssolutionsolution

Example -Example -

What is the molarity of an What is the molarity of an aqueous solution containing aqueous solution containing 40.0g of glucose (C40.0g of glucose (C66HH1212OO66) ) in 1.5 L of solution?in 1.5 L of solution?

How many grams of NaOH How many grams of NaOH are in 250mL of a 3.0M are in 250mL of a 3.0M NaOH solution?NaOH solution?

3.Dilution Formula3.Dilution Formula

MM11VV11 = M = M22VV22

Example – Example – What volume of a 3.00M KI What volume of a 3.00M KI

stock solution would you use stock solution would you use

to make 0.300L of a 1.25Mto make 0.300L of a 1.25M

KI solution?KI solution?

4. molality4. molality

mm = = mols molssolutesolute

kilogramskilogramssolventsolvent

Example -Example -

What is the molality of What is the molality of a solution containing a solution containing 30.0g of naphthalene 30.0g of naphthalene (C(C1010HH88) dissolved in ) dissolved in 500.0g of toluene? 500.0g of toluene?

How many grams of How many grams of water would be water would be necessary to make of necessary to make of 1.35 m salt solution 1.35 m salt solution from 25.8 g of NaCl?from 25.8 g of NaCl?

5. Mole Fraction5. Mole Fraction

XXAA ==

mols molsAA

total molstotal mols

Examples-Examples- What is the mole fraction of What is the mole fraction of

NaOH in an aqueous solution NaOH in an aqueous solution that contains 22.8% NaOH by that contains 22.8% NaOH by mass?mass?

An aqueous solution of NaCl An aqueous solution of NaCl has a mole fraction of 0.21. has a mole fraction of 0.21. What is the mass of NaCl What is the mass of NaCl dissolved in 100.0mL of water?dissolved in 100.0mL of water?

Colligative Colligative PropertiesProperties

Properties of solutions that Properties of solutions that are affected by the number are affected by the number of particles, but not by the of particles, but not by the identity of the particles.identity of the particles.

(it doesn’t matter what is (it doesn’t matter what is dissolved, only how much!)dissolved, only how much!)

1. Vapor Pressure 1. Vapor Pressure LoweringLowering

Vapor pressure is caused Vapor pressure is caused by molecules that have by molecules that have evaporated from the evaporated from the surface of a liquidsurface of a liquid

For a solution, the For a solution, the amount of vapor amount of vapor pressure (vapor above pressure (vapor above the solution) will be the solution) will be less.less.

Why?Why?

When solute is added, When solute is added, particles of solute particles of solute replace some of the replace some of the solvent at the surface. solvent at the surface. This reduces access for This reduces access for evaporation, thus evaporation, thus reducing vapor pressure.reducing vapor pressure.

Also,Also,

In a solution the solvent-In a solution the solvent-solute attraction is solute attraction is usually stronger than the usually stronger than the original solvent-solvent original solvent-solvent attraction, further attraction, further reducing evaporation.reducing evaporation.

Raoult’s lawRaoult’s law

PPAA = X = XAAPPAA°°

PPAA= new vapor pressure of= new vapor pressure of the solutionthe solutionXXA A = mol fraction of the= mol fraction of the solventsolventPPAA° = original vapor pressure of ° = original vapor pressure of the solventthe solvent

exampleexample

Calculate the vapor Calculate the vapor pressure of a solution pressure of a solution prepared by dissolving 25.0 prepared by dissolving 25.0 grams of NaCl in 100 grams grams of NaCl in 100 grams of water. The original vapor of water. The original vapor pressure of the water is pressure of the water is 19.8 torr.19.8 torr.

2. Boiling point 2. Boiling point elevationelevation The difference between the The difference between the

normal boiling point of a normal boiling point of a pure pure solventsolvent and the boiling point and the boiling point of a of a solutionsolution..

∆∆TTbb = K = Kb b mm

KKb Hb H22O O = 0.51 = 0.51 °C·Kg/mol°C·Kg/mol

exampleexample

What is the boiling point of What is the boiling point of a solution of 103.2 g of a solution of 103.2 g of CC66HH1212OO66 in 0.75 Kg of H in 0.75 Kg of H22O?O?

What is the molality of a What is the molality of a water solution that boils at water solution that boils at 106.5°C?106.5°C?

3. Freezing point 3. Freezing point depressiondepression The difference between the The difference between the

normal freezing point of a normal freezing point of a pure solventpure solvent and the freezing and the freezing point of a point of a solutionsolution..

∆∆TTff = K = Kf f mm

KKf Hf H22O O = -1.86 = -1.86 °C·Kg/mol°C·Kg/mol

exampleexample

What is the freezing What is the freezing point of water in a point of water in a solution of 117.1g of solution of 117.1g of sucrose (Csucrose (C1212HH2222OO1111) and ) and 200 g of water?200 g of water?

4. Osmotic Pressure4. Osmotic Pressure

OsmosisOsmosis – the diffusion of solvent – the diffusion of solventparticles across a semipermeable particles across a semipermeable membrane from an area of high membrane from an area of high solvent concentration to an area solvent concentration to an area

of of lower solvent concentration.lower solvent concentration.

Why is this a colligative property?Why is this a colligative property?

Hypertonic Hypertonic Hypotonic Hypotonic solution solution

solutionsolution

ΠΠ = MRT = MRT

The average osmotic The average osmotic pressure of blood is 7.7 pressure of blood is 7.7 atm at 25°C. What atm at 25°C. What concentration of glucose, concentration of glucose, CC66HH1212OO66, will be isotonic , will be isotonic with blood?with blood?

Types of MixturesTypes of Mixtures

1.1. Homogeneous mixture Homogeneous mixture

SolutionSolution - parts too - parts too small to see. (all looks small to see. (all looks the the samesame) Solvated ) Solvated particles are less than 1 particles are less than 1 nm.nm.

2. Heterogeneous 2. Heterogeneous mixturesmixtures

Suspension – a mixture Suspension – a mixture containing particles containing particles large enough to settle large enough to settle out if left undisturbed.out if left undisturbed.

Particles > 1000 nmParticles > 1000 nm

Examples - Examples -

–Muddy waterMuddy water–Medicines (shake well)Medicines (shake well)–PaintPaint

ColloidColloid – mixture with – mixture with intermediate sized particles.intermediate sized particles. the particles are too small the particles are too small

to filter out or to settle out to filter out or to settle out on their own. on their own.

(between 1 nm and 1000 (between 1 nm and 1000 nm)nm)

Examples - Examples -

FogFog

BloodBlood

ButterButter

FoamFoam

SmokeSmoke

The Tyndall EffectThe Tyndall Effect

Colloids can be cloudy Colloids can be cloudy (opaque) or as clear as (opaque) or as clear as solutions.solutions.

Particles in a colloid are Particles in a colloid are always big enough to scatter always big enough to scatter light – the light – the Tyndall effect Tyndall effect

The Tyndall effect is used to The Tyndall effect is used to distinguish between solution distinguish between solution and colloids.and colloids.

Brownian motionBrownian motion

This erratic movement of colloid This erratic movement of colloid particles resulting from particles resulting from collisions of particles of the collisions of particles of the dispersion medium with the dispersion medium with the dispersed particles. These dispersed particles. These collisions prevent the colloid collisions prevent the colloid particles from settling out of particles from settling out of the mixture.the mixture.

Enthalpies of SolutionEnthalpies of Solution

Three steps in the dissolving Three steps in the dissolving processprocess

1.1. Breaking the solute-solute attractionBreaking the solute-solute attraction*(energy required)*(energy required)

2.2. Breaking the solvent-solvent attractionBreaking the solvent-solvent attraction*(energy required)*(energy required)

3.3. Formation of the solute-solvent Formation of the solute-solvent attractionattraction*(energy released)*(energy released)

Enthalpy of SolutionEnthalpy of Solution

If the sum of steps 1 & 2 is If the sum of steps 1 & 2 is greater than step 3, the process greater than step 3, the process is is endothermicendothermic (feels cold) (feels cold)

If the sum of steps 1 & 2 is less If the sum of steps 1 & 2 is less than step 3, the process is than step 3, the process is exothermicexothermic (feels hot) (feels hot)

Concepts to know…Concepts to know…

Electrolyte vs. nonelectrolyteElectrolyte vs. nonelectrolyte Factors affecting rate of Factors affecting rate of

dissolutiondissolution Unsaturated, saturated, Unsaturated, saturated,

supersaturatedsupersaturated Miscible vs. immiscibleMiscible vs. immiscible