Unit 3

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Unit 3
2012-09-28 15:33:44

Calculations with Chemical Formulas and Equations
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  1. Mole
    Allows us to count by weighing. One mole of a substance has a mass in grams equal to its formula mass.
  2. Molar mass
    The molar mass in grams per mole is numereically equal to the formula mass in amu

    1amu = 1 gram/mole
  3. Avogdro's number
    6.0221367 * 1023 atoms

    6.022 * 1023 atoms / mole
  4. Calculating molar mass
    • 1. look at the  # of atoms of one type in the formula
    • 2. look on the periodic chart for the mass of that atom.
    • 3. multiply the mass by the number of atoms
    • 4. do this for each type of atom, then add them up
    •  molar mass has units of grams/mole
  5. Mass to Moles
    • Calculatge the molar mass
    • Arrange the molar mass as a conversion factor to cancel out the appropritate units
    • Calculate
  6. Mass to Particles
    grams -> mole -> atoms

    • find molar mass
    • Arrange avogadro's number as a conversion factor to cancel out the appropriate units
    • Calculate
  7. Conversion within a Chemical Formula-example H2O
    • Stoichiometic equivalency (pertaining to or involving substances that are in the exact proportions required for a given reaction) between any two atoms or compounds.
    • 2atoms H / 1 H2O molecule
    • 2 mole H atom / 1 mole O atom
    • 2 atoms H / 1 atom O
  8. Conversion within a Chemical Formula
    • Mass A <-> Moles A <-> Moles B <-> Mass B
    • find molar mass
    • set up dimensional analysis and calculate
  9. Percentage Composition
    • list of elements in a compound by percentages of mass (parts per hundred)
    • can be calculated from decomposition data or from chemical formula.  part / whole * 100
    • percentages should equal 100%
  10. Theoretical percentages by mass
    • Assume 1 mole sample
    • calculate molar mass - convert from mole to gram then add mass together
    • calculate percentage composition.  parts / whole * 100
  11. Combustion analysis
    • Involves burining a sample of a compound to determine its chemical formula
    • Compounds are seldom broken up into their elements-they are changed into other compounds
  12. Elementa Combustion Analysis
    • Calculate part of each element in the compound.
    • mass compound ->mole compound -> mole element ->mass element
    • Calculate the mass percentage
    • parts / whole * 100
  13. Emperical formula
    smallest whole number ratio of atoms in a formula
  14. Molecular formula
    actual formula for a molecule
  15. Molecular formula-given empirical formula and molar mass
    mass of molecular formula / mass of emirical formula

    multiply by empirical formula for molecular formula
  16. Emperical formual-calculation
    • seperate element from compound if necessary
    •  mass element -> mole element = answer/ smallest unit for all elements being considered.
  17. Chemical equations
    descibes the chemical reaction
  18. Balanced equations
    has the same number of each type of atom and the same charge on each side of the equation
  19. Coefficients
    in a balanced equation it tell us the stoichiometric relationship between the components in a reaction and can be used as conversion factors.
  20. Conversion factors for chemical reactions
    • Moles A <-> Moles B
    • write chemical equation and balance it
    • find stoichiometric relationship between elements
    • look at units to decide what should be on top, then calculate