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OB_ Mole class _2 Calculating Molar Masses_ and numbers

VIEWS: 1 PAGES: 18

									          OB: Mole class #2
      Calculating Molar Masses,
and numbers of atoms in any mass of an
       element or compound



     Reference tables and calculators
          mandatory right now
What is molar mass? How do we calculate it? What does it mean?
What’s the name for this compound?


Al(MnO4)3              __________________________

How do we calculate what one mole of this weighs?
              (how many moles of each part are in one mole of compound?)


Al(MnO4)3
Al
Mn
O
What is molar mass? How do we calculate it? What does it mean?
What’s the name for this compound?


Al(MnO4)3              __________________________

How do we calculate what one mole of this weighs?
              (how many moles of each part are in one mole of compound?)


Al(MnO4)3
Al     1 x 27 g/mole =                 27 g

Mn 3 x 55 g/mole =                    165 g

O 12 x 16 g/mole =                    192 g

                                  384 g/mole
NYS Regents likes vocabulary. They like to use extra words like…

Gram Molecular Mass - another way to say molar mass for a molecular compound
                      which forms into molecules

Or

Gram Formula Mass - another way to say molar mass for an ionic compound that
                    makes formula units


Both of these mean molar mass,
the number of
grams in one mole of a substance.




It’s just vocabulary,
so don’t be fooled.
What is the gram molecular mass (the molar mass) of SULFUR TRIOXIDE?




so3
What is the gram molecular mass (the molar mass) of sulfur trioxide?




SO3
S 1 mole x 32 g/mole = 32 grams

O 3 moles x 16 g/mole = 48 grams                                       This picture is for fun.
                                                                       The shoes Dorothy is
                         80 grams in one mole                            wearing are in the
                                                                       Smithsonian Museum
                                                                       in Washington, DC. I
Or, the molar mass of sulfur trioxide is 80 grams                         saw them there.

Or, if you have 80 grams of SO3, you have a mole of SO3

Or, 80 grams of SO3 = 6.02 x 1023 molecules of SO3
Calculate the gram formula mass (molar mass) of sodium sulfate. (write formula correctly first)



__________________________
Calculate the gram formula mass (molar mass) of sodium sulfate.




Na2SO4
  Na      2 mole x 23 g/mole =                46 grams

   S       1 mole x 32 g/mole = 32 grams

  O        4 mole x 16 g/mole = 64 grams


                                             142 g/mole
Using the concept of moles and molar mass, you can
determine how many moles are present in a given mass
of a substance.

For example

If you have 100.0 g of Nickel, how many moles do you have?

  100.0 g Ni
      1


                    Start at the beginning (please use units)
Using the concept of moles and molar mass, you can
determine how many moles are present in a given mass
of a substance.

For example

If you have 100.0 g of Nickel, how many moles do you have?

  100.0 g Ni x 1 mole Ni =       1.695 moles of Nickel
      1         59 g Ni




  4 SF           Unlimited SF         Needs 4 SF too
551 grams of gold is how many moles of gold?




37.33 grams of silicon is how many moles of silicon?
551 grams of gold is how many moles of gold?

 551 g Au       1 mole Au =
    1
            x
                197 g Au
                            2.80 moles Au




37.33 grams of silicon is how many moles of silicon?

 37.33 g Si         1 mole Si =
     1
                x
                     28 g Si
                                1.333 moles Si
thirteen
                    As you remember:
        1 mole of anything has 6.02 x 1023 particles
How many moles of zinc are in 1.25 x 1023 atoms?

1.25 x 1023 atoms Zn   x        1 mole Zn
                                                  =
          1                6.02 x 1023 atoms Zn




    1.25        1023
    6.02
            x
                1023
                       =     0.208 moles zinc
                                       3 SF
                    of xen on gas
          ny moles4          f Xe?
 H ow m a        2 atoms o
             x 10
are in 5.75
How many moles of xenon gas
are in 5.75 x 1024 atoms of Xe?
5.75 x 1024 atoms of Xe x          1 mole Xe
                            6.02 x 1023 atoms of Xe   =
           1



                     24
5.75 x 10
          23
             moles =
6.02 10


          0.955 x 101 moles Xe = 9.55 moles Xe
            Last slide o’ the day
• If you find 50.0 grams of pure silver, how
  many atoms of silver did you find?
• A hint might be required, this is a two step problem,
  first convert grams to moles, then
• Convert moles to atoms
• This is the real beginning of mole math, a bigger
  problem, you can do it (go slowly)
  50.0 g Ag         1 mole Ag
                X                 =    0.463 moles Ag
      1              108 g Ag




 0.463 mole Ag        6.02 x 1023 atoms Ag
               X                                 =
       1                    1 mole Ag




0.463 x 6.02 x 1023 atoms Ag = 2.79 x 1023 atoms of silver
                                      3SF

								
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