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Unit 2 Section C

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  1. Unit 2 Section C Conservation

  2. C.1 Keeping Track of Atoms • In some reactions, matter seems to appear and others matter seems to disappear. • Matter seems to disappear in our daily lives. • Gas in tank, food we eat, etc.

  3. Basically, “using things up” means changing materials chemically, not destroying them. • Law of Conservation of Matter- matter is not created nor destroyed

  4. Recall, that reactants are on the left of a chemical equation and products are on the right. C + O2 CO2 Note that the numbers of carbon and oxygen are the same on both sides.

  5. Cu + O2 CuO Note that the number of Cu and O are not equal. To balance the equation, coefficients need to be used to get the same # on both sides 2Cu + O2 2CuO

  6. Formula Unit- refers to the smallest unit of an ionic compound. • Molecules refer to covalently bonded compounds.

  7. C.2 Nature’s Conservation: Balanced Chemical Equations • Conservation works because atoms are indestructible. • To balance equation, start by doing an atom inventory. That is, are the numbers of each atom equal on both sides. • See page 131-132.

  8. Additional Rules • If polyatomic ions, such as NO3 and CO2, treat as a unit. • Balance H and O last.

  9. C.3 Atom, Molecule, and Ion Inventory • It is not very useful to talk about single atom or formula units in an equation. • Chemists use a counting unit called the mole • You are familiar with a “pair” or “dozen”

  10. One mole equals 602000000000000000000000 of anything. • Or 6.02 x 1023 • This is called Avogadro’s number

  11. See the first paragraph on page 136. • Molar mass – mass of one mole of any substance. • Equal to the mass on the periodic table

  12. In a balanced equation, the coefficient equals the number of molecules but also the moles of the same substances 2Cu + O2 2CuO This means 2 moles of copper reacts with 1 mole of oxygen to produce copper (II) oxide

  13. C.4 Composition of Materials • One helpful property of matter is Percent composition- percent by mass of a material in a substance Helpful to determine what elements to mine from what ores.

  14. What is the percent composition of Cu in Cu(NO3)2?

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