Chemistry: Matter and Change

Chapter 3

 

1. Matter is anything that occupies space and has mass.

2. A substance is a form of matter that has a definite composition and distinct properties.

Chemistry is the study of matter and thechanges it undergoes

water, ammonia, sucrose, gold, oxygen

1.4

A mixture is a combination of two or more substances in which the substances retain their distinct identities.

1. Homogenous mixture – composition of the mixture is the same throughout.

2. Heterogeneous mixture – composition is not uniform throughout.

soft drink, milk, solder

cement, iron filings in sand

1.4

Physical means can be used to separate a mixture into its pure components.

magnet

1.4

distillation

An element is a substance that cannot be separated into simpler substances by chemical means.

• 116 elements have been identified

• 82 elements occur naturally on Earth

gold, aluminum, lead, oxygen, carbon

• 34 elements have been created by scientists

technetium, americium, seaborgium

1.4

A compound is a substance composed of atoms of two or more elements chemically united in fixed proportions.

Compounds can only be separated into their pure components (elements) by chemical means.

Water (H2O) Glucose (C6H12O6)

Ammonia (NH3)

1.4

1.4

Kinetic Nature of MatterKinetic Nature of Matter

Matter consists of atoms and molecules in motion.

STATES OF MATTERSTATES OF MATTER• SOLIDS — have rigid shape, fixed

volume. External shape can reflect the atomic and molecular arrangement.– Reasonably well understood.

• LIQUIDS — have no fixed shape and may not fill a container completely. – Not well understood.

• GASES — expand to fill their container. – Good theoretical understanding.

OTHER STATES OF MATTEROTHER STATES OF MATTER

• PLASMA — an electrically charged gas; Example: the sun or any other star

• BOSE-EINSTEIN CONDENSATE — a condensate that forms near absolute zero that has superconductive properties; Example: supercooled Rb gas

Physical or Chemical?

A physical change does not alter the composition or identity of a substance.

A chemical change alters the composition or identity of the substance(s) involved.

ice meltingsugar dissolving

in water

1.6

hydrogen burns in air to form water

An extensive property of a material depends upon how much matter is is being considered.

An intensive property of a material does not depend upon how much matter is is being considered.

• mass

• length

• volume

• density

• temperature

• color

Extensive and Intensive Properties

1.6

Law of Definite Proportions

• A compound is always composed of the same elements in the same proportions by mass, no matter how large or small the sample. – Examples:– Water 2 hydrogens and 1 oxygen

• It is always the ratio for H to O to make water.

Law of Multiple Proportions

• When two different compounds are formed rom the same elements, different masses of the elements combined in different ratios.– Example: water and hydrogen perioxide

Classification of Mixtures• homogeneous = mixture that has uniform

composition throughout – Every piece of a sample has identical characteristics,

though another sample with the same components may have different characteristics.

– atoms or molecules mixed uniformly

• heterogeneous = mixture that does not have uniform composition throughout – contains regions within the sample with different

characteristics– atoms or molecules not mixed uniformly

15

Changes in Matter

• Changes that alter the state or appearance of the matter without altering the composition are called physical changes.

• Changes that alter the composition of the matter are called chemical changes.– During the chemical change, the atoms that are present rearrange

into new molecules, but all of the original atoms are still present.

16

Solution• a mixture of two or more substances that is

identical throughout• can be physically separated• composed of solutes and solvents

the substance in the smallest amount and the one that dissolves in the solvent

the substance in the larger

amount that dissolves the solute

Colloids (milk, fog, jello) are considered solutions

Iced Tea Mix(solute)

Water(solvent)

Iced Tea(solution)

Salt water is considered a

solution. How

can it be physically separated?

What are the different ways of separating mixtures?

• Magnetism• Hand separation• Filtration• Sifting or sieving• Extraction and evaporation• Chromatography

Magnetism

• If one component of the mixture has magnetic properties, you could use a magnet to separate the mixture. Iron, nickel, and cobalt are all materials that are magnetic.

• Not all metals are magnetic: gold, silver, and aluminum are examples of metals that are not magnetic.

Hand separation

• Separating the parts of a mixture by hand.

• Only useful when the particles are large enough to be seen clearly.

• Useful for: separating parts of a salad.

Example of hand separation:

• Using your fork to separate tomatoes, lettuce, cucumber, onions, etc. in your salad.

Filtration

• Used when separating a solid substance from a fluid (a liquid or a gas) by passing a mixture through a porous material such as a type of filter.

• Works by letting the fluid pass through but not the solid.

• Examples of filters: coffee filter, cloth, oil filter, even sand!

Evaporation• Allowing the liquid

to evaporate, leaving the soluble solid behind.

• Example: heating sugar water. The water evaporates and the sugar crystals are left behind.

Example of using extraction and evaporation together:

• Using water to dissolve sugar, then letting the water evaporate, leaving the sugar behind.

Chromatography• Used to separate dissolved substances in

a solution from each other.

Mixture Components

Separation

Stationary Phase

Mobile Phase

Example of chromatography:

• Using chromatography paper to separate ink into it’s original components.

Percent Composition (mass)

• Sometimes it’s useful to know the composition of a compound in terms of what percentage of the total is each element

• Percent– “Parts per 100”– The number of specific items per a group

of 100 items– 50% of $100 is $50 (50 items/100 total

items)

Percent Example• You have 4 oranges and 5 apples. What

percent of the total is oranges?

• In “parts per 100”

oranges 44%100% total9

oranges 4

oranges 44%100% total100

oranges 44

Percent Composition• It is the percent by mass of each element in a

compound• Can be determined

– By its chemical formula– Molar masses of the elements that

compose the compound • The percent of each element contributes to

the mass of the compound

compoundainelement100%

compoundtheofmassmolarelementeachofmasseachofpercentmass

Calculating Percent Composition Example

• What is the percent composition of each element in NH4OH?

g14.01 = g14.011:N g5.04 = g0078.15:H g16.00 = g00.611:O

g35.05 = %100

g35.05

g14.01 :N

%100g35.05

g5.04 :H

%100g35.05

g16.00 :O

N 39.97%

H 14.38%

O 45.65%

Determine the contribution of each element

Molar mass