1. Compounds, Mixtures, and Reactions
Unit II-Part 5

2. Classifying Matter Matter Pure Substances Mixtures milk, tea Fe, O
Homogeneous
Heterogeneous
Elements
Compounds
Rocky Road ice cream, muddy water
milk, tea
Fe, O
H2O, CO2

3. What is a Pure Substance?
A pure substance is a classification of matter that includes both elements and compounds
Pure substances cannot be separated by physical means such as distillation, filtration, or chromatography

4. Elements We have already studied elements
An element is made of one kind of atom
Found on the periodic table

5. What Is A Compound?
A compound is a pure substance that is created by 2 or more elements chemically reacting and joining together
Ex: NaCl, H2O, CO2, NH3, NaHCO3, and C6H12O6
Notice that elements combine in many ways to make compounds
Ex: H2O, H2O2, CO, and CO2

6. Why Do Compounds Form?
Compounds form to allow elements to become more stable
Na is flammable when it comes in contact with H2O, and Cl2 is a toxic gas
NaCl is a very stable compound that is neither flammable nor toxic (in normal quantities)
Compounds that are extremely unstable will break down to form the more stable elements

7. How Do Compounds Form?
Compounds form by the interaction between the nuclei and valence electrons of 2 or more elements
THE OCTET RULE: an element is most stable with 8 valence electrons
Elements will join chemically to get 8 valence electrons
Ex: CO2 : oxygen has 6 valence electrons and carbon has 4
If the carbon shares 2 with each oxygen, everyone will have 8 valence electrons!

8. What Do Compounds Have To Do With My Life?
Compounds are the substances that make up ALL living and non-living things
Examples: Where would you be without:
H2O—water
NaCl—table salt
C3H8O—rubbing alcohol
C55H98O6—an example of an
unsaturated fat

9. What Is A Mixture?
A mixture is the physical combination of 2 or more substances
It is important to understand that a mixture is not chemically combined
Mixtures can be separated by physical means such as filtration, distillation, and chromatography
Mixtures can be divided into 2 groups
Homogenous mixtures
Heterogeneous mixtures

10. How Do Mixtures Form?
Mixtures form by physically “junking” 2 or more substances together
Remember no chemical change is occurring
The formation of a mixture is not a result of lowering energy

11. What Is a Homogenous Mixture?
A homogeneous mixture is a mixture that is evenly distributed
Homogeneous mixtures are commonly called solutions.
Solution = Solute + Solvent
Solute: “stuff” being dissolved
Solvent: “stuff” doing the dissolving
The solvent is present in greater quantity
The solute is present in the lesser quantity
Ex: Salt water: Salt=solute, Water=solvent

12. What Is a Heterogeneous Mixture?
A heterogeneous mixture is a mixture that is unevenly distributed.
Examples:
Iced tea: The ice is floating at the top and therefore is not evenly distributed throughout the tea
Chex Mix: You may find a different number of pretzels or Chex cereal in each handful; therefore, the mixture is unevenly distributed

13. How Are Mixtures Important To My Life?
We encounter mixtures everywhere in our lives
Where would you be without:
Ice cream
Kool-aid
Shampoo
Soup
Milk
Orange juice

14. How Can We Change Matter Into New Substances?
Chemical reaction (also known as a chemical change) is a change in a substance or substances that results in a totally new substance
Ex: 2H2(g) + O2(g)  2H2O(g)
Notice that the reactants (the substances you start with) combine to form a new substance (the product)

15. How Do I Know If A Chemical Reaction Has Occurred?
There are 5 indicators of a chemical reaction
Evolution of a gas
Evolution of light
Evolution of heat
Color change
Evolution of a precipitate
Precipitate: an insoluble substance that is produced as result of a chemical reaction

16. Why Do Chemical Reactions Occur?
Chemical reactions occur to produce a more stable product than the existing reactants
Ex: 2Na(s) + Cl2(g)  2NaCl(s)
*The sodium is highly unstable and the chlorine gas is somewhat unstable. The resulting Sodium Chloride is VERY stable.
**It is important to understand that the products have totally different properties than the reactants

17. Where Does The Matter Go?
It is important to understand that when matter undergoes a chemical reaction (ie a chemical change) it does not disappear or appear
The atoms are rearranged and form new bonds, but no matter is lost nor gained
This is called the Law of Conservation of Matter

18. What Kind of Chemical Reactions Do I Experience?
The acidic milk and basic baking soda that produce CO2 gas when a cake bakes
Paper burning to produce ashes, CO2, and H2O vapor
Hydrogen peroxide decomposing to produce water and oxygen gas