Solutions Chapter 15 Pure & Impure - PowerPoint Presentation

Slide1

Solutions

Chapter 15Slide2

Pure & Impure

If a material is pure, it consists of only a single element or compound

If the material is impure, then it is a mixture or contains two or more elements or compounds

Do not be fooled by labels that claim their product is pure… “pure 100% orange juice”

Mixtures are termed either heterogeneous or homogeneousSlide3

Mixtures

A mixture is a combination of two or more substances in which each substance retains its properties

Most materials we see daily are mixtures

Mixture of elements, compounds or both

The components of a mixture can be separated from one another by taking advantage of differences in the components’ physical properties

Solids and liquids can be separated by filter paper (

Filtration

)Slide4

Different Mixtures

Remember what the prefixes mean…

Hetero: different

Homo: same

Heterogeneous mixtures

are when the different components can be seen as individuals

e.g. sand in water, pulp in orange juice, salad dressings

Homogeneous mixtures

have the same composition throughout, therefore any region of the mixture has the same ratio of substancesSlide5

Heterogeneous Mixtures

Suspension

: a mixture containing particles that settle out if left undisturbed for a period of time

These particles are larger than those found in solvated particles and gravity has greater force on them

***Particles in a solution are atomic-scale size***

Fog or

jello

Colloids

:

Mixtures of medium sized particles (between suspensions and solutions

Fine sand, silt in water or tomato juice (milk too)Slide6

Heterogeneous MixturesSlide7

Homogeneous Mixtures - Solutions

To describe a solution correctly, one must know the lingo or proper terms

The component that is present in the largest amount is the

solvent

The other component is the solute

Yes you can have more than one solute

Think of it like this… you pour the chocolate syrup (

SOLUTE

) into the milk (

SOLVENT

)

In other words, you usually mix the solute into the solvent

Anything that does not mix in the solvent is said to be

INSOLUBLE

Have you ever seen something come out of the liquid solution when it cools? This substance is the solute and is known as the

PRECIPITATE

Lastly, the term for mixing these components into the solution is known as

DISSOLVING

!!!Slide8

Solution, Suspension, ColloidSlide9
Slide10

Tyndall Effect

Put a beam of light through a mixture

Reflection of light off undissolved particles

Which one is the solution, colloid and suspension?

A

B

CSlide11

SolutionSlide12

ColloidSlide13

SuspensionSlide14

Dissolving

How do they dissolve?

The solvent forces the solute apart into individual components and completely surrounds them

This forms the solution and is called

solvation

Factors that affect the rate of dissolving:

Increasing surface area

Agitating the solution

Heating the solventSlide15

Dissolving of Salt in Water

NaCl(

s

) + H

2

O

 Na

+

(

aq

) + Cl

-

(

aq

)

Cl

-

ions

Na

+

ions

Water moleculesSlide16
Slide17

100 mL

Interstitial Spaces and Particle Size

Interstitial spaces

(holes in water where substances dissolve)

Parking at school if you arrive at

8:00

AM = _____

Parking at school if you arrive at

9:10 AM

= _____

More available spaces if you arrive early. Salt dissolves quicker when you

begin because there are more available spaces to '

park'

.

Analogy: Compact car is easier to park than SUV.

STIR

Easy

Hard

Theory: Crush salt to make particles smaller (increase surface area)

…it will dissolve more rapidly.Slide18

Electrolytes

A substance that dissolves in water to give a solution that conducts electric current

These are salts (metal – nonmetal)

Some of the most important chemicals in our body our electrolytes (they are in sport drinks)

A

nonelectrolyte

is a chemical that dissolves in water but does not allow it to conduct electricitySlide19

Electrolytes

Electrolytes: solutions

that carry an electric current

NaCl(

aq

) Na

+

+ Cl

-

HF(

aq

) H

+

+ F

-

strong electrolyte

weak electrolyte

nonelectrolyteSlide20

General Solubility GuidelinesSlide21

Net Ionic Equations

These equations include only those compounds and ions that undergo a chemical change in a reaction in an aqueous solution

Solids dissolve (dissociate in water)

Ca(OH)

2

 Ca

+2

+ 2OH

-

Show the net ionic equation for zinc nitrate and ammonium sulfide:

Zn(NO

3

)

2

+ (NH

4

)

2

S  2 NH

4

NO

3 (?)

+

ZnS

(?)

Zn

2+

+ 2NO

3

-

+ 2NH

4

+

+ S

2-

 2NH

4

+

+ 2NO

3

-

+

ZnS

(s)

Zn

2+

+ S

2-  ZnS

White ions are spectator ionsSlide22

Further Examples

FeCl

3 (

aq

)

+

NaOH

(

aq

)

→ Fe(OH)

3 (s)

+

NaCl

(

aq

)

LiNO

3

+

KCl → KNO3 + LiCl

Write and Balance the Net Ionic EquationsSlide23

Solubility

Equilibria

Some ionic compounds will dissociate into their respective ions completely when added to water

NaCl

(s)

→

Na

+

(

aq

)

+ Cl

-

(

aq

)

These are

strong electrolytes

Some dissociate then return back to solid form and then dissociate again (and again…)

BaSO

4

(s)

⇋

Ba

2+

(

aq

)

+ SO

4

2-

(

aq

)

You can solve for the equilibrium constant for this dissociate reactions as well

These are

weak electrolytesSlide24

Solubility

Equilibria

BaSO

4 (s)

⇋

Ba

2+

(

aq

)

+ SO

4

2-

(

aq

)

The equation would be:

In the equilibrium expression above, [BaSO

4

] is constant because it’s a solid

Therefore, you can cross-multiply (or multiply each side by [BaSO

4

]) to get

K

eq

* [BaSO

4

]

This creates a constant called the solubility product constant -

K

sp

 Slide25

Solubility Product Constant

K

sp

is very similar to

K

eq

, equilibrium constant for reversible reactions, because it deals with the equilibrium of ions that have not completely disassociated

To solve any problems that would occur asking for solubility of ionic compounds, simply set the

K

sp

equal to the

cation

and anion concentrations found in the right side of the equilibrium reaction

If there are coefficients in the balanced reactions, then you will still use them as exponents

K

sp

= [cation

+

]

C

* [anion

-

]

ASlide26

Mixing Solutions in Solutions

Liquids

Liquids that don’t want to mix with other liquids like oil and vinegar salad dressing is known as

immiscible

Therefore,

miscible

liquid solutions are those that are soluble in one another

Gases

Henry’s Law:

The solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid

If the gas is escaping from a liquid, it is known as

effervescence

CO

2

from sodas, the commercials of

alka

seltzer Slide27

Too Much Stuff

You can add too much solute to the solvent and it will not mix or dissolve any longer

This point is known as the

saturation point

and we are left with a saturated solution

Saturation

is defined as the maximum amount of material something can hold onto (Think of humidity levels with weather)

Super-Saturated Solutions

If you can still add solute to the solution, then it is an

unsaturated solution

Therefore we can generate yet another equation

 Slide28

Solution Concentration

Percent by Mass

=

This will be used to calculate concentration ratios of mixtures and will later be needed to calculate molarity, molality, etc.

 Slide29

Concentrated vs. Dilute

We use these general terms to describe solutions that are saturated or still moderately unsaturated, respectively

Here it comes… to get around counting all the individual components, chemists use a unit to measure the number of any particle

MOLE!!!! A mole is equal to 6.02 x 10

23

Mole

is derived from the Latin word for “pile”

The term

molarity

then refers to the number of moles of solute/liters of solution

602,000,000,000,000,000,000,000 particlesSlide30

Molarity

Molarity

(

M

) is the number of moles of solute dissolved per liter of solution

M

is read as molar

The denominator must always be in L

A 100.5

mL

intravenous (IV) solution contains 5.10 g of glucose (C

6

H

12

O

6

). What is the

molarity

of the solution?

 Slide31

Molarity Practice

1. What is the

molarity

of a solution containing 21.0 g

NaCl

in 200

mL

of solution?

2. How do you prepare 250

mL

of a 0.500 M

NaOH

solution?Slide32

Preparing Molar Solutions

You are now ready to prepare solutions that your teacher used to make for you all morning long

But wait! Do you always use 1 L of solution in those glass reagent bottles?

NO!!!!

So here is how you dose it out in smaller quantities…Slide33

Preparing Molar Solutions

If you need 1.50

M

of glucose but only 100

mL

, how would you prepare this solution.

Normally, you would get 1.50 moles of glucose (~270 g) and place it in (< 1 L of water) to make 1000

mL

solution.

100

mL

1.50

M

x

1 L

x

270 g C

6

H12O6 = 27.0 g

1000 mL 1 L solutionSlide34

Molality (m)

Yet another form of measuring concentrations gives the use of moles expressed in moles per kilogram

 Slide35

Molality Problems

1) Calculate the

molality

when 75.0 grams of MgCl

2

is dissolved in 500.0 g of solvent. 

2) 150.0 grams of sucrose (C

12

H

22

O

11

, mol. wt. = 342.3 g/mol) is dissolved in 1.00 L of water. What is the

molality

? 

3) 29.5 grams of KI is dissolved in 1.25 kg of solvent. What is the

molality

? Slide36

Preparing Solutions

Diluting Solutions

When making solutions from concentrated stock supplies, you can dilute it down to make it a lower concentration

Because the total number of moles of solute does not change, only the volume of the solution

M

1

V

1

=

M

2

V

2

Where

M

1

& V

1

represent the molarity and volume of the stock solution and M

2

& V

2

represent the molarity and volume of the dilute solutionSlide37

Dilution Problems

1. Your teacher needs to make a 0.500 M solution of

HCl

from concentrated 12.0 M

HCl

. If the volume of the dilute needs to be 500

mL

, then how many

mL

of the concentrated does he need to mix with how much water? (Remember the final total volume is 500

mL

).

2. It is necessary to make a 0.500 M solution of

HCl

from 500.0

mL

of a 3.00 M solution of

HCl

. What is the volume of the new solution?

3. What is the

molarity

of a solution which has a volume of 1500.0

mL

if it was obtained by diluting 250.0

mL

of a 6.0 M solution of H

2

SO

4

?

4. Your teacher needs to make 500.0

mL

of a 3.00 M solution of H

2

SO

4

. Concentrated H

2

SO

4

from the chemical company is 18.0 M. How many

mL

of the concentrated acid is needed to dilute with how much water to make this solution? Slide38

Colligative Properties

The

colligative properties

of a solution depend primarily on the

number

of solute particles present rather than the

kind

of particles.

There

are four colligative properties:

1. Boiling-point elevation

2. Freezing-Point depression

3. Vapor pressure

4. Osmotic pressure

Water boils at 100°C but what happens when you add salt?

What if you boil water at very high altitudes?