Compounds, Mixtures, and Reactions

Unit II-Part 5

Classifying MatterMatter

Pure Substances Mixtures

Elements Compounds

Homogeneous Heterogeneous

Fe, O H2O, CO2

milk, tea Rocky Road ice cream, muddy water

What is a Pure Substance?

• A pure substance cannot be separated by physical means.

• It is a classification of matter that includes both elements and compounds

Elements

• We have already studied elements−An element is made of one kind of

atom− Found on the periodic table

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

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)

Can a compound be reversed?

http://www.youtube.com/watch?v=OTEX38bQ-2w “Breaking Down Water”- Anode: The anode of a device is the

terminal where current flows in from outside.

- Cathode: The cathode of a device is the terminal where current flows out.

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

What Do Compounds Have To Do With My Life?

• Compounds are the substances that make up ALL living and non-living things

• http://www.pslc.ws/mactest/level1.htm

• Examples: Where would you be without:−H2O—water

−NaCl—table salt

−C3H8O—rubbing alcohol

−C55H98O6—an example of an

unsaturated fat

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

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: liquid it is dissolved into

• The solvent is present in greater quantity

• The solute is present in the lesser quantity− Ex: Salt water: Salt=solute,

Water=solvent

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

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

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)

How Do I Know If A Chemical Reaction Has Occurred?

• There are 5 indicators of a chemical

reaction.

1. Evolution of a gas2. Evolution of light3. Evolution of heat4. Color change5. Evolution of a precipitate

Precipitate: an insoluble substance that is produced as result of a chemical reaction.

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

Where Does The Matter Go?

• It is important to understand that when matter undergoes a chemical reaction (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

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