Pure Substances vs.

Mixtures

Using the characteristic

properties of substances to

separate mixtures

Characteristic Properties

What are some characteristic properties of

substances?

Appearance

Odor

Density

Melting Point

Boiling Point

Heat Capacity, Heat of Fusion, Heat of

Vaporization

Magnetic

Solubility

Solubility

Will something dissolve in something else?

Will sugar dissolve in water?

Will sugar dissolve in ethanol?

Solvent- the substance that is doing the

dissolving

Water is universal solvent

Solute- what is being dissolved

Pure Substances

How do we define the word “pure?”

unmixed with any other matter

The simplest of pure substances are

elements.

Elements cannot be broken down into

simpler substances.

A single particle of an element is

called an atom.

Pure Substances

Elements can be combined through

chemical reactions to form compounds.

We can use the word molecule for particles

of compounds.

Compounds are pure substances because

they contain only type of molecule.

Compounds must be separated by chemical

means and cannot be separated by physical

means.

Pure Substances

The most famous compound:

WATER

H2O

What evidence do you have

that the formula is H2O?

Hoffman Apparatus

A Hoffman Apparatus is

used to break down

water into hydrogen and

oxygen gas. A chemical

reaction must take place

to do this and it

happens because of the

electricity that is applied

to the water.

Mixtures

A mixture is comprised of two or more pure

substances.

Composition can be described as variablemeaning the substances composing a mixture can

be combined in any amount.

Example: saltwater can be made of one grain of salt in

a gallon of water or a cup of salt in a gallon of water.

Mixtures can be separated by physical means

because the substances that are mixed keep their

individual properties.

Type of Mixtures

Mixture Example

Gas-Gas Air is primarily a mixture of nitrogen, oxygen, and water vapor, carbon dioxide, and argon gases

Gas-Liquid Carbonated beverages contain carbon dioxide gas dissolved in solution.

Liquid-Liquid Vinegar contains acetic acid dissolved in water.

Solid-Liquid Sweetened powder drink contains sugar and other solid ingredients dissolved in water.

Solid-Solid Steel is an alloy of iron containing carbon. Brass is an alloy containing copper and zinc.

Mixtures

There are two types of mixtures:

Heterogeneous Mixtures – can have substances in

the same phases or different phases. When you look

at a heterogeneous mixture, you can see that two or

more substances have been mixed.

Lucky Charms Cereal

Bowl of Mixed Candy

Ethanol & Sugar Cube

Homogeneous Mixtures- have only substances in the

same phase. When you look at them, you see a

uniform substance.

Milk

Ethanol & Water

Sugar & Water

Separating Mixtures

We can exploit individual substances’properties in order to separate a mixture.

Separation depends on a difference of physical

properties.

Let’s say we had a mixture of ethanol and

water.

Ethanol has a boiling point of 78.4oC and water

has a boiling point of 100.0oC.

The different boiling points can be used to

separate the mixture by using distillation.

Distillation Apparatus

Heat Curve of Ethanol and

WaterT

em

pera

ture

(o

C)

100.0

78.4

0.0

Time

Other Methods of Separation

How could you separate a mixture of salt and

sand?

Start by listing some properties of salt and of

sand. Differences in this list can be exploited to

separate the mixture.

Is salt water-soluble?

Is sand?

Could water be used to separate the two?

How could the water be recovered from the salt?

Filtration

Filtration is a technique

that uses a porous

barrier to separate a

solid from a liquid

Used for separation of

solids present in a liquid

Heterogeneous

mixtures composed of

solids and liquids are

easily separated by

filtration

Particle Diagrams

How can we represent the mixing of sugar

and water?

Sugar + Water = Sugar & Water Mixture

Iron & Sulfur Mix vs. Compound

What are the properties of the iron & sulfur

mixture?

How can the mixture be separated?

What are the properties of the iron (II)

sulfide?

What would have to happen to separate this

compound?

Particle Diagrams

How can we represent a sample of the

iron/sulfur mixture and the iron (II) sufide.

Iron/Sulfur Mix Iron (II) Sulfide

Summary Questions

Can a mixture be separated? If

so, how?

Can a compound be

separated? If so, how?

Can an element be separated?

If so, how?