Chemistry: (d) Mole Conversions, Molecular/Empirical Formulas, Stoichiometry, Molarity, Limiting Rea

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Chemistry: (d) Mole Conversions, Molecular/Empirical Formulas, Stoichiometry, Molarity, Limiting Rea
2011-06-11 12:52:13

chemistry (unit 5)
Show Answers:

  1. Why are moles used?
    You can't directly count atoms, moles are used instead
  2. Does the molar masses of 2 difference substances or the number of particles in a mole always remain the same?
    number of particles in a mole
  3. What do each of the letters in the ideal gas law (PV=nRT) stand for?
    pressureXvolume= number of molesXgas constantXtemperature
  4. In the ideal gas law, what unit must the volume and the temperature always be in?
    • Volume: liters
    • Temperature: kelvin
  5. What are molecular formulas the same as?
    empirical formulas or some whole number multiple of it
  6. What are the three steps to getting a molecular formula?
    • 1) get empirical
    • 2) divide molar mass from problem by molar mass from the empirical formula
    • 3) multiple subscripts by answer to #2
  7. What are the two things empirical formulas show?
    • the lowest whole number ratio of elements
    • actual numbers of atoms in molecules
  8. What are the four steps for empirical formulas?
    • 1) assume % is grams
    • 2) convert grams to moles
    • 3) divide by smaller number
    • 4) multiply to get whole numbers
  9. What is a skeleton equation?
    unbalanced equation
  10. What are the 7 elements that exist as diatomic molecules?
    hydrogen, nitrogen, oxygen, florine, chlorine, bromine, iodine
  11. What is the definition of sstoichiometry?
    using balanced equations to determine the amounts of R needed to create a specific amount of P
  12. Why do we care about stoichiometry?
    • companies use stoichiometry to reduce waste, keep costs down and create products that work
    • we use ideas of stoich in everyday lives
  13. What is molarity?
    moles of solute per liter of solution
  14. What is a solute? Give an example.
    substance which dissolves (like NaCl)
  15. Why do we need molarity?
    for aqueous solutions b/c molar mass cannot be used for them
  16. T or F? 100g of NaCl (aq) is different than 100g of NaCl (s).
  17. What is the equation for molarity?
    M=moles over liters
  18. How can you tell if the problem is a limiting reagent one?
    more than one reactant amount is given
  19. How do you do a limiting reagent problem?
    • convert 1st reagent to product (g)
    • convert 2nd reagent to product (g)
    • pick lowest one
  20. How can you tell if a problem is one, two or three steps?
    • one- moles to moles
    • two- moles to something else or something else to moles
    • three- no moles mentioned
  21. What does percent yield measure?
    how much of the expected product you actually get