Compounds, Mixtures, and Reactions

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Compounds, Mixtures, and Reactions

• Unit II-Part 5

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

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Elements

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

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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

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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

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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!

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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
• H2Owater
• NaCltable salt
• C3H8Orubbing alcohol
• C55H98O6an example of an
• unsaturated fat

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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

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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

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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 Saltsolute, Watersolvent

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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

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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

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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)

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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

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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

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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

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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