1. Chemistry: Matter and Change
Chapter 3

2. water, ammonia, sucrose, gold, oxygen
Chemistry is the study of matter and the
changes it undergoes
Matter is anything that occupies space and has mass.
A substance is a form of matter that has a definite composition and distinct properties.
water, ammonia, sucrose, gold, oxygen
1.4

4. Heterogeneous mixture – composition is not uniform throughout.
A mixture is a combination of two or more substances in which the substances retain their distinct identities.
Homogenous mixture – composition of the mixture is the same throughout.
soft drink, milk, solder
Heterogeneous mixture – composition is not uniform throughout.
cement,
iron filings in sand
1.4

5. Physical means can be used to separate a mixture into its pure components.
distillation
magnet
1.4

7. 116 elements have been identified
An element is a substance that cannot be separated into simpler substances by chemical means.
116 elements have been identified
92 elements occur naturally on Earth
gold, aluminum, lead, oxygen, carbon
34 elements have been created by scientists
technetium, americium, seaborgium
1.4

9. 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

11. Kinetic Nature of Matter
Matter consists of atoms and molecules in motion.

12. STATES 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.

13. OTHER 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

14. Physical or Chemical?
A physical change does not alter the composition or identity of a substance.
ice melting
sugar dissolving
in water
A chemical change alters the composition or identity of the substance(s) involved.
hydrogen burns in air to form water
1.6

15. Extensive and Intensive Properties
An extensive property of a material depends upon how much matter is is being considered.
mass
length
volume
An intensive property of a material does not depend upon how much matter is is being considered.
density
temperature
color
1.6

16. 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.

17. 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

18. 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 18 18

19. 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. 19 19

21. Solution
a mixture of two or more substances that is identical throughout
can be physically separated
composed of solutes and solvents
Salt water is considered a solution. How
can it be
physically separated?
the substance in the smallest
amount and the one that dissolves in the solvent
the substance in the larger
amount that dissolves the solute
Iced Tea Mix
(solute)
Water
(solvent)
Iced Tea
(solution)
Colloids (milk, fog, jello) are considered solutions

22. What are the different ways of separating mixtures?
Magnetism
Hand separation
Filtration
Sifting or sieving
Extraction and evaporation
Chromatography

23. 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.

24. 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.

25. Example of hand separation:
Using your fork to separate tomatoes, lettuce, cucumber, onions, etc. in your salad.

26. 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!

27. 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.

28. Example of using extraction and evaporation together:
Using water to dissolve sugar, then letting the water evaporate, leaving the sugar behind.

29. Chromatography
Used to separate dissolved substances in a solution from each other.
Mixture
Components
Separation
Stationary Phase
Mobile Phase

30. Example of chromatography:
Using chromatography paper to separate ink into it’s original components.

31. 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)
The number of items of a specified type in a group of 100 items

32. Percent Example
You have 4 oranges and 5 apples. What percent of the total is oranges?
In “parts per 100”

33. 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
The formula of carbon dioxide indicates it is composed of one atom of carbon and two atoms of oxygen. Now we will express it in terms of mass percent

34. Calculating Percent Composition Example
What is the percent composition of each element in NH4OH?
Determine the contribution of each element
Molar mass
On a per mol basis

35. We will talk about this section later.