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Compounds, Mixtures, and Reactions

Compounds, Mixtures, and Reactions. Classifying Matter. Matter. Pure Substances. Mixtures. Homogeneous. Heterogeneous. Elements. Compounds. Rocky Road ice cream, muddy water. milk, tea. Fe, O. H 2 O, CO 2. What is a Pure Substance?.

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Compounds, Mixtures, and Reactions

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  1. Compounds, Mixtures, and Reactions

  2. Classifying Matter Matter Pure Substances Mixtures 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 • 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 decreasing or increasing 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 • Matter is not lost or gained in a chemical or physical change

  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

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