Home Up E1 E2 E3 E4 Topics - E1 Topics E2 Topics E3 Topics E4 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 27 28 29 30 31



I. The three states of matter

Solid - a state of matter in which the component particles are in contact with each other; a solid has a definite volume and definite shape

Liquid - A state of matter in which the molecules are weakly associated; it has a definite volume but an indefinite shape

Gas - a substance that has no definite shape or volume ; the particles in a gas are far apart because there is little or no attraction between them.

Vapor - the gaseous state of a substance that normally exists as a solid or liquid at room temperature.

II.  Pure component or mixture?

water - pure
syrup - carbohydrates (sugars), colorings, flavorings
potato - >150 substances or chemicals (elements or compounds)

Mixtures are a combination of different substances (elements and compounds)

Kinds of mixtures

1. Homogeneous - completely uniform, components equally distributed, "solutions" - salt water, vodka, syrup

2. Heterogeneous - not uniform - components not equally distributed - granite, pepperoni pizza

III. Separating Mixtures - Lots of ways, each based on exploiting differences in properties - here are a few examples

1. Size - separating gold  - use sieve

2. Density - separating gold - "pan"

3. Magnetic character - Demo: Iron (magnetic) from corn flakes

4. Boiling point  - common way to separate liquids

Vodka - Primary components - 30% alcohol (ethanol), 70% water
boiling point - water = 100oC, ethanol  78oC, ethanol comes off first
Demo: separating water and copper sulfate.

IV. Pure substances - (obtained after complete separation)

a. uniform properties

b. definite composition

c. can't be further separated

Types of pure substances

1. Element - a substance that cannot be broken down into simpler substances by chemical means (tabulated in the periodic table, carbon, silicon, gold, etc...).  Made up entirely of atoms of the same "type"

2. Compound - substance formed by a chemical combination of one or more elements in which component elements are in a fixed whole number ratio.  Compounds consists of atoms of different elements chemically bound together.  Can be decomposed into other elements or compounds by a chemical process.  

Demo: pure substance vs. mixture 
mixture of iron (Fe) + sulfur (S)  vs. pyrite (compound with Fe:S = 1:2, FeS2)
pyrite is not magnetic, iron is. 

Summary - FIGURE 1.2 - The Classification of Matter

V. Properties of Matter

1. Physical properties - the property of a substance that can be measured without changing the composition of the substance.

2. Chemical properties - the characteristics of a substance with respect to the manner in which it reacts with other substances.

Physical or Chemical property?

1. What color is it? PP
2. Will it rust? CP  forming iron oxide from iron
3. What is the boiling pt? PP
4. Does it sublime? PP
5. Does it conduct electricity? PP
6. Does it smell? PP
7. Does it burn? CP  ideal combustion of a fuel - react with oxygen to form water and carbon dioxide
8. Does it explode? CP  many explosions involve the production of gases that lead to a large increase in volume.  Sodium azide in air bags explodes to yield nitrogen gas that inflates the air bag. 

VI. Physical or Chemical Changes

Physical change - conversion that does not change the substance composition - tends to be reversible
melting -> solid-liquid <- freezing
evaporation -> liquid-gas condensation
sublimation -> solid-gas


Chemical change - change in composition of matter

reactant -->  product

Back to our iron and sulfur example

Can heat the mixture and make the compound pyrite

iron + sulfur -> iron sulfide (one for of which is pyrite)


Identifying a chemical change vs. physical change can be difficult


Some signs of a chemical change

1. change in a property

a. color change - e.g. copper patina

copper + oxygen + water + carbon dioxide -> "basic copper carbonate (pale green)"

b. odor change - e.g. rotting fish

primary smell comes from molecules belonging to a class of compounds know as amines, two particular amines are aptly named putrescine (1,4 diaminobutane) and cadaverine (1,5 diaminopentane, NH2(CH2)5NH2).  An amine you are likely familiar with is household ammonia (solution of ammonia in water).

c. change in magnetic properties (pyrite example above)

2. Change in physical state at a given temperature (forming a gas from a solid as in the air bag example above)

always have to be careful though, these are not absolute

e.g. The smell (and loss of it) from a "scratch and sniff" is not due to a chemical change.  Evaporation of an odiferous substance.