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Solution ChemistryUnit 8

General ChemistrySpring ’13

Objectives (Ch. 15)

� Understand and describe the basic properties of water and ice and how they effect the world around you.

� Explain the high surface tension and low vapor pressure of water in terms of the structure of the water molecule and hydrogen bonding (15.1.1)

� Distinguish between solvent and solute (15.2.1)

� Describe what happens in the solution process (15.2.2)

� Explain why all ionic compounds are electrolytes (15.2.3)

� Distinguish between suspension and solution (15.3.2)

� Identify the distinguishing characteristic of a colloid (15.3.2)

WATER AND ITS PROPERTIES

15.1

Simply Water

� Ice has a low density. (Does ice float?)

� It’s a polar molecule

� Slightly positive (+) on one end

� Slightly negative (-) on another

� Look what it does to salt!

� It also easily bonds to itself and easily pulls compounds apart

Polar vs. Non-polar?

� It’s like a tug of war…

� Even pulling of

electrons means it’s

non-polar

� Uneven pulling means it’s polar

Water’s Hydrogen Bond

� Water molecules are not connected

by full covalent bonds, but they’re pretty strong

� The formation between the hydrogen

atoms on one molecule and a highly

electronegative atom on another is called a hydrogen bond.

� Atoms that can do this are hydrogen,

oxygen, fluorine, and nitrogen

� Keep reading…

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Hydrogen Bonds cont.

� Any molecule with O-H bonds has the potential to form hydrogen bonds.

� Alcohols (molecules with O-H bonds) also form hydrogen bonds.

� Have similar properties to water

� Proteins, nucleic acids, and carbohydrates also can form hydrogen bonds.

� How they form and shape determines how they’re used biologically

Basic Properties of Water

� Boils at 100oC

� Freezes at 0oC

� Expands due to hydrogen bonding

� Solid state is highly organized

� One drop = ~2x1021 molecules

Surface Tension

� Surface tension: the inward force, or pull, that tends to minimize the surface area of a liquid� Causes drop to pull together

� All liquids have a surface tension� Mercury has high surface tension

� Surfactants� Interfere with H-bonding and reduce

surface tension

� Soaps and detergents

Surface Tension at work

Vapor Pressure of Water

� Results from the molecules escaping from the surface of the liquid and

entering the vapor phase.

� In water, H-bonds hold on to water

molecules tightly

� Tendency for molecules to escape is low

� Evaporation of water is low

� What would happen if it was fast?!

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Specific Heat of water

� Specific heat: measures the amount of heat, in joules, needed to raise the temperature of 1g of

substance by 1oC.

� For water it’s 4.18, pretty high.

� Why it takes so long to boil water

� It takes a long time to absorb or release more heat

for its temperature to change 1oC than a lot of other

substances.

� Think of a pool in the summer time.

Specific Heat

Substance Specificheat

Water 4.18

Chloroform 0.96

Aluminum 0.90

Mercury 0.14

Water in the Solid State

� The structure of ice is a regular open framework of water molecules arranged like a honeycomb.

� Add energy and the

framework collapses

� The molecules are closer

together making water more dense than ice

� Implications on aquatic life?

HOMOGENEOUS AQUEOUS SYSTEMS

15.2

Water: The Universal Solvent(Homogeneous Aqueous Systems)

� Almost always found in solution

� A very good solvent due to its polar abilities

� Examples of aqueous solutions

� Milk

� Soda pop

� Coffee and tea

� Tap water

� Look at the ingredient list of a liquidy beverage. Water is probably there.

Solutions

� When one substance dissolves into another, that is called a SOLUTION

� Example: sugar water, Kool-Aid

� There are two main parts of a solution:� SOLUTE= the dissolved material

� Example: sugar, salt, oxygen (air)

� SOLVENT= the substance that is doing the dissolving (usually a liquid)� Usually present in the highest amount

� Example: Water, nitrogen (air)

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The Solution Process

� Water, a polar molecule, is capable of dissolving a range of compounds

� As individual solute ions break away from the crystal, the negative and positive ions become

surrounded by solvent molecules and the ionic crystal dissolves

The Solution Process Cont.

� Ionic solids are composed of positive and negative ions.

� Water has a positive and negative end (it’s polar)

� Opposites attract and the ionic compounds

separate into ions.

� The process by which charged particles in an

ionic solid separate from one another is solvation

“Like Dissolves Like”

� This means that dissolving occurs when similarities exist between the solvent and the solute.

� Sugar is a polar molecule, so is water, and water tends to dissolve substances that are polar or that form hydrogen bonds.

� Oil and water don’t mix.� Oil is nonpolar

� But different oils are “like” enough to mix and stay mixed.

� Oil and gasoline.

Electrolytes vs. Nonelectrolytes

� Electrolyte

� A compound that conducts an electric current when it is in an aqueous solution

� All ionic compounds are electrolytes because they dissociate into ions

� Nonelectrolyte� A compound that does not conduct an

electric current in aqueous solution

� Many covalents are this because they are not composed of ions

The electric pickle

HETEROGENEOUS AQUEOUS SYSTEMS

15.3

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Suspensions

� A (heterogeneous) mixture from which particles settle out upon standing

� A suspension differs from a solution because the particles are much larger

and do not stay suspended indefinitely

� Cornstarch mixed with water thickens

sauces

Suspensions

� At least two substances are clearly identified

� Think of a glass of water with sand or mud in it.

� Typically easy to separate

Colloids

� A heterogeneous mixture containing particles that range in size from 1nm to 1000nm

� Particles spread throughout the dispersion medium (s, l, g)� Glues

� Gelatin

� Paint

� Aerosol sprays

� Smoke

� Difficult to sep. due to the tiny size of particles

Colloid Examples (Table 15.3)Tyndall Effect, Coagulation

� Tyndall Effect

� The scattering of visible light by colloidal particles

� Suspensions also do this but solutions don’t.

� Coagulation

� The clumping of particles in a colloid

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Emulsions� A colloidal dispersion of a

liquid in a liquid (that don’t easily mix)

� Must have an “emulsifying agent”

� To form the emulsion

� To maintain stability

� Ex) soap, detergent, egg yolk

� Mayonnaise is a mixture of oil and vinegar

� Milk and margarine are too, some cosmetics

Objectives (Ch. 16)

� Identify the factors that determine the rate at which a solute dissolves (16.1.1)

� Identify the units usually used to express the solubility of a solute

(16.1.2)

� Identify the factors that determine the mass of solute that will dissolve in a

given mass of solute (16.1.3)

PROPERTIES OF SOLUTIONS

16.1

Solution Formation

� Determining factors

� Composition of solvent

� Composition of the solute

� Speed of dissolving factors

� Stirring (agitation)

� Temperature

� Surface area

� All involve contact between solvent and solute

Rate of Dissolving

� Stirring the Solution

� Increases the interaction

between water molecules and

the solute.

� Solute and solvent interact more often, the rate of dissolution is

faster.

� Does not influence the amount

of solute that will dissolve

� Oil will never mix with water

not matter how long you stir or shake that Italian dressing

Rate of Dissolving

� Heating the Solution

� Increases kinetic energy of the water molecules

� Increases frequency and force of the collisions between solute and solvent

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Rate of Dissolving

� Grinding the solute� Creates more surface area

(remember the big fireball

demo?)

� Solvent molecules attack the

edged surfaces of solute crystals.

� The more surface area

exposed, the faster the rate

of dissolving

Solubility

� The amount of solute that dissolves in a given amount of solvent at a specified temperature and pressure to produce a saturated solution

� Units

� grams of solute per 100g of solvent

Types of Solutions

� Saturated solution

� Solution holding the max. amt. Of solute

per amt. Of solution under given

conditions.

� Add more solute it won’t dissolve

� Unsaturated solution

� The amt. of solute is less than the max that

could be dissolved.

� Add more solute it will dissolve

Solutions

� Supersaturated solution

� Contain more solute than the usual max.

amt. And are unstable.

� Add a crystal and it fills the container with

crystals

FACTORS AFFECTING SOLUBILITY

Temperature� Solubility of most solid substances

increases as the temperature of the

solvent increases

� How supersaturated solutions are made

� Heat up above sat. pt and slowly cool down

so more solute is dissolved than can be

dissolved at that temp

� The effect of temp on the solubility of gases in liquids is opposite

� The solubility of most gases are greater in

cold water than in hot

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Effects of Pressure

� Huge effect on gases, very little on solids and liquids

� Gas solubility increases as the partial pressure of the gas above the solution increases. (direct

relationship)

� Ex) Soda bottle has lots of dissolved CO2 in it which

is forced in at the plant.

� When you open the bottle you hear a hiss and CO2

starts escaping from the bottle decreasing the

concentration of CO2 in the bottle

Objectives

� Solve problems involving the Molarity of a solution (16.2.1)

� Describe the effect of dilution on the total moles of solute in solution (16.2.2)

� Define percent by volume solutions (16.2.3)

Solution Concentration (16.2)

� What does concentration mean?

� It tells us how much solute is dissolved in a

given volume of solution

� “dilute solution” has a small amount of

solute

� “concentrated solution” has a large amount

of solute

� Both are relative and are very imprecise

� Qualitative… not quantitative

Molarity

� You can describe the precise concentration quantitatively with Molarity.

� Molarity (symbol M).

� Relates the amount of solute to a given volume of

solution.

� The number of moles of solute dissolved in one liter of solution.

� Ex) a solution labeled 3M NaCl is read “three molar

sodium chloride solution”

Molarity

� Expressed in this manner:

� How do you convert from grams to moles?

Divide by molar mass foo!

Hint: what is the equation for density?

mass

Density volume

Molarity

� Drain cleaner is made with caustic sodium hydroxide,

NaOH. The Dow company prepares a bottle of drain cleaner from 24.0 g of NaOH dissolved in 0.100 L of

solution. What is the molarity?

Molar mass of NaOH (40.00 g/mol)

24.0g NaOH 1 mol NaOH

mol NaOH

= L solution = 6.00M NaOH0.100 L solution 40.00g NaOH

We want Liters, leave this alone Units for molarity

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Molarity- Writing Unit Factors

� We can solve molarity calculations by using the solution concentration as a unit

factor.

� Example: 6.00M solution of NaOH contains 6.00 mol of solute in each liter of solution.

� Written as:

6.00 mol NaOH or 1 L solution

1 L solution 6.00 mol NaOH

There’s 1000mL in 1L

Preparing Solutions

� How would you prepare 1.0L of a 0.15M sodium chloride solution? I.O.W. How many grams NaCl are needed?

� Think: First, determine the mass of NaCl to add to a 1.0 L

container. The 0.15M solution must contain 0.15 moles of NaCl per

liter of solution (definition of molarity).

1. Use molarity to convert to moles.

2. Then use molar mass to go from moles to grams.

1.0 L solution 0.15 mol NaCl 58.5 g NaCl = 8.8 g NaCl

1 1 L solution 1 mol NaCl

Making that solution

1. Obtain a volumetric flask

2. Measure 8.8 g of NaCl

3. Add solute to a small

amount of water, about 300 mL, to dissolve

4. Add enough additional

water to bring the total

volume to 1.0 L, to the etched line on flask

Preparing a Different Volume

of Solution

� How would you prepare 5.0 L of a 1.5M solution of glucose, C6H12O6

� Think: You need to determine the number of grams of glucose to add to a

5-L container. The 1.5M solution has 1.5 mol of glucose (use this to convert to grams.

5.0 L solution 1.5 mol glucose 180 g glucose

= 1400 g glucose1 1 L solution 1 mol glucose

MOLARITY MOLAR MASS

Making Dilutions

� Stock solutions of acids are very concentrated

� HNO3 comes in 15.8M

� H2SO4 comes in 18.0M

� HCl comes in 12M

� This does not tell how “nasty” these are…that’s a

different unit

� Using an acid in this concentration is incredibly

dangerous

� I dilute them for lab purposes… how?

Acid burn(why you don’t wear flip flops in the lab)

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Dilutions

� Diluting a solution reduces the # of moles of solute per unit volume

� The total number of moles of solute in solution does not change� mol solute before dilution = mol solute after dilution

� Equation for dilutions:

� M1 x V1 = M2 x V2

� M1 and V1 are initial readings

� M2 x V2 are for the diluted solution

� Units of volume must match (mL or L)

Dilution example� How many milliliters of 2.00M MgSO4 must be diluted with

water to prepare 100.0mL of 0.400M MgSO4?

� M1= 2.00M M2=0.400M

V1= ? V2= 100mL

� M1 x V1 = M2 x V2

Dilution answer

� Substitute and solve for V1

� 20 mL

� Take 20mL of initial solution and dilute with

enough water to increase volume to 100

mL

� DO NOT ADD 100mL of water, this will

give 120mL of solution, not 100mL

Dilution Example #2

� If you take 10mL of a 3.42M solution and dilute to 100mL, what is your new concentration?

� M1 x V1 = M2 x V2

� (10mL)(3.42) = (M2)(100mL)

� M2 = 0.342M

Dilution Example #3

� You need a 2.10M solution. You need 1500mL of it. How much of a 12M solution do you need

to use?

� M1 x V1 = M2 x V2

� (12M)(V1) = (2.10M)(1500mL)

� V1 = 262.5mL

Percent Solutions

� How many mL of isopropyl alcohol are in 100mL of a 70% solution?

� 70 mL are mixed with enough water to make 100 mL

� % by Volume = volume of solute x 100%volume of solution

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Graphing Solubilityremember….

� The solubility of substances changes with temperature

� For example, is it easier to dissolve sugar

in hot or cold coffee?

� Solids become more soluble at higher

temperatures

� Gases become less soluble at higher

temperatures

Solubility Curves (cont.)

� Scientist have studied many

substances solubility at different temperatures

� They created

graphs which show

this data

Solubility Curves (cont.)

� Let’s simplify the graph with all the substances down to just one substance

Solubility of KCl in 100 g of water

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Temperature (degrees Celcius)

Gra

ms o

f so

lute

dis

so

lved

in

100 g

of

wate

r

Solubility Curves (cont.)

Is KCl a

solid or gas in this

graph?

Solubility of KCl in 100 g of water

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10

20

30

40

50

60

70

0 20 40 60 80 100 120

Temperature (degrees Celcius)

Gra

ms o

f solu

te d

issolv

ed in

100 g

of

wate

r

Solubility Curves (cont.)� How many grams of KCl will dissolve in

500g of water at 80°C?

� 260g of KCl (52g x 5 = 260g)

Solubility of KCl in 100 g of water

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Temperature (degrees Celcius)

Gra

ms o

f solu

te d

issolv

ed in 1

00 g

of

wate

r

Solubility Curves (cont.)� How many grams of water will it take to dissolve

26 g of KCl at 80°C?� 50g of H2O (1/2 of what dissolves in 100g H2O)

(% of 100g: 26g/52g=.50)

Solubility of KCl in 100 g of water

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Temperature (degrees Celcius)

Gra

ms o

f solu

te d

issolv

ed in 1

00 g

of

wate

r

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Solubility Curves (cont.)� If one dissolves 95 grams of KCl in 250

grams of water at 80°C, what kind of

solution will they have?

� Unsaturated

Solubility of KCl in 100 g of water

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120

Temperature (degrees Celcius)

Gra

ms o

f solu

te d

issolv

ed in 1

00 g

of

wate

r

You need to determine the saturation point before you can

decide the type of solution.

(Sat. pt. from graph)x(%H2O)

52 g x 2.5 = 130 g

Saturation point in 250g of water

Practice Problem #1

� How many grams of NH4Cl will dissolve in

300 grams of water at 70°C?

� If one dissolves 137.5 grams of NaNO3 in 125

grams of water at 45°C, what kind of solution will they have?

186g NH4Cl

(62g x 3)

Saturated

110g x 1.25= 137.5 The same as what it asks