The Identification of Matter

NO YES

NO YES YESNO

NO YES

Element Compound

Pure SubstanceCan it be chemically decomposed?

Colloid Suspension

HeterogeneousAre the particles visible?

Solution

Homogeneous

MixtureIs the composition uniform?

MatterCan it be physically separated?

Review of Pure SubstancesThere are two types of pure substances:

1. ElementsElements are composed of one kind of atom. Examples are on the periodic table.

2. CompoundsCompounds are composed of two or more elements chemically combined in a fixed ratio

When the atoms of the elements combine chemically they form molecules of a compound

Examples: H2O, NaCl, C2H5OH, Fe2O3

Examples of atoms of elements forming molecules of compounds

A.

B.

A. One carbon atom and one oxygen atom make one molecule of carbon monoxideB. One carbon atom and two oxygen atoms make one molecule of carbon dioxide

Examination of Mixtures

1. Solutions

2. Suspensions

3. Colloids

There are three types of mixtures:

Uniformly mixed, homogeneous mixtures of two or more pure substances

Heterogeneous mixtures of two or more pure substancesin which the substances are visible with the naked eye

Heterogeneous mixtures of two or more pure substancesin which the particles of the substances are too small to be seen with the naked eye, but separate out over time.

Examples of Solutions:

An aqueous solution of copper sulfate(Water and copper sulfate)

An aqueous solution of potassium dichromate(Water and potassium dichromate)

The Metallic alloy - Brass ( a mixture of copper and zinc)

Other examples:air (mixture of gases)water and ethyl alcohol water and oxygen gas

All solutions have a solute and a solvent

For example: If 5.0 grams of table salt (solute) is completely dissolved in 100 mL of water (solvent)

The concentration of the aqueous salt solution = 5.0 g/100 mL

Solutions always have a concentration The concentration can be expressed as a solute to solvent ratio

When a solid is dissolved in a liquid, the solid is termed the solute, the liquid the solvent.

When one liquid is dissolved in a second liquid, the liquid present in the smaller amount is usually called the solute. (the same for a gas in a gas)

Depending on the concentration, liquid solutions can be:

1. Unsaturated In an unsaturated solution more solute may be dissolved in the solvent at a given temperature

2. SaturatedIn a saturated solution no more solute can be dissolved in the solvent at a given temperature

3. SupersaturatedIn a supersaturated solution more than the predictednormal maximum amount of solute has been dissolved.

A supersaturated solution can be created when a liquid solution is heated and then slowly cooled.

Liquid solutions can be separated physically by using evaporation

A solution heated in an evaporation dish

Examples of heterogeneous mixtures and suspensions (note: suspensions have a liquid or gas component)

oil and vinegar - a suspension (if shaken)sand and water - a suspension (if shaken)iron, sulfur and salt - a solid heterogeneous mixture

Heterogeneous Mixtures - Suspensions

A rock is formed from a number of substances mixed heterogeneously

Certain rocks are solid heterogeneous mixtures

Suspensions in liquids have two or more visibly obvious components, in which, the components can be separated

physically by filtration or decantation

Filtration Decantation

Heterogeneous Mixtures - Colloids

milk shaving cream

fog marshmellowsjello pearlsmustard mayonnaise

The particles in colloids are in between the size of those in solutions and those in suspensions.

Colloids look homogeneous, but are not.

Liquid colloids will separate out slowly over time.

Examples of Colloids:

Colloids are often opaque, which means, you can not see through them.

But sometimes liquid colloids can be clear and can be confused or mistaken for a solution!

If one is not sure, there is a way to find out.

By using something called The Tyndall Effect

The Tyndall Effect

The Tyndall Effect is used with gas and liquid mixtures.It is a method by which a clear solution and a clear colloidCan be identified.

Light is passed through the unknown liquid or gas mixture.Since Light bounces off of particles, the greater the particle size the more light will be seen.

If the reflected light is visible to the naked eye, then the mixture is considered to be a colloid

colloid solution (or a pure liquid)

The Tyndall Effect

The laser light travels through the solution with little or noreflection of light, while the beam is very obvious in the colloid.

light source

http://www.silver-lightning.com/tyndall/

solutionsolution suspensionsuspension colloidcolloidhomogeneoushomogeneous heterogeneousheterogeneous heterogeneousheterogeneous

Very tiny particles do Very tiny particles do not settle outnot settle out

Larger particles settle Larger particles settle out quite quicklyout quite quickly

Particles larger than Particles larger than those in a solution those in a solution will eventually settle will eventually settle outout

NoNo Tyndall effect Tyndall effect Tyndall effectTyndall effect Tyndall effectTyndall effect

NoNo separation by separation by filtration or filtration or decantationdecantation

Separation by Separation by filtration or filtration or decantationdecantation

NoNo separation by separation by filtration or filtration or decantationdecantation

A Comparison of Liquid Mixtures

A Comparison of Mixtures and Compounds

MixtureMixture CompoundCompound

1.1. Components may be in any proportionComponents may be in any proportion Components are in fixed proportionsComponents are in fixed proportions

2.2. Individual components retain their own Individual components retain their own propertiesproperties

Individual components lose their Individual components lose their identities. A new set of properties resultidentities. A new set of properties result

3.3. Components may be separated by Components may be separated by physical meansphysical means

Components may only be separated by Components may only be separated by chemical meanschemical means

4.4. When mixed there is little, if any When mixed there is little, if any evidence of a chemical change. evidence of a chemical change.

When combined there is evidence of a When combined there is evidence of a chemical change (heat, light, gas chemical change (heat, light, gas production, precipitate). production, precipitate).

5. 5. It is a physical combination of pure It is a physical combination of pure substancessubstances

It is a chemical union of atoms of It is a chemical union of atoms of elements, to form molecules of elements, to form molecules of compoundscompounds

Identify the following as:element, compound, solution, suspension, colloid

peanut butter

nitrogen

ethanol

cement

oil and water

salt water

lithium

steel

ketchup

whipped creamair

water

carbon

milkcarbon dioxide

sand and ethanol water and vinegar