The Mole Concept and Avogadro's constant by qO4RDQ31


									The Mole Concept and Avogadro's constant
        The Mole-at first glace
 What is “the mole”?
 Dictionary definition: “a small burrowing mammal
  with dark velvety fur, a long muzzle, and very small
  eyes, feeding mainly on worms, grubs, and other
 Animal?- must be biology-not chemistry!
 Are we in the right class?
            The Mole-demystified
 Another definition-”Amount of
  substance…”- more like chemistry!
                                          Ream of paper (500)
 Pair of socks           Dozen of eggs
 (2)                     (12)
                      The mole & coins!

 Suppose you had to count a vast number of coins
 What is the quickest method?
 If the mass of a certain number of coins is known, the total number can be
  weighed and then the amount can be calculated.
      The Mole-demystified 2
 Quantity of 6.02x1023
 Why this magic number?
 It is the number of particles present in exactly 12 grams
  of the isotope carbon-12
 Called the Avogadro Constant
                      The mole
 If you weigh out 12g of carbon-12, you will get 6.02x1023
  of carbon atoms
                    The mole
 All elements measured relative to carbon-12
 Amount of substance (mol)= number of particles/6.02 x
 Number of particles= amount of substance (mol) x 6.02 x
 Mole is the same number regardless of the representative
  particle: atom, molecule, ion, electron
The mole
                  Example 1
 Calculate the number of molecules of water in 0.01mol
  of water
 Number of water molecules=0.01mol x 6 x 1023 mol-1 = 6
  x 1021
 How many carbon atoms are there in 0.02 mol of
  carbon dioxide?
 How many oxygen atoms are there in 0.02 mol of
  carbon dioxide?
                Molar Mass
 Molar mass is the mass of 1 mole of the substance
 Number of moles=mass in g/mass of 1 mole in g
 A mole of carbon atoms, C, has a mass of 12g
 A mole of hydrogen atoms, H, has a mass of 1g
 BUT a mole of hydrogen molecules has a mass of
        Molar mass- example
 Calculate the molar mass of aluminium sulfate,
 2 x Al= 2 x 26.98g/mol= 53.96g/mol
  +3 x S= 3 x 32.06g/mol= 96.18g/mol
  +12 x O= 12 x 16.00g/mol=192.00g/mol
Molar mass= 342.14g/mol
     Relative atomic mass, relative
             formula mass
 Relative atomic mass- the weighted average mass (according to relative
  abundances) of all the naturally occurring isotopes of an element
  compare with an atom of the carbon-12 isotope, which has a mass of
  exactly 12
 Formula= 12 x average mass of one atom of the element/mass of one
  atom of carbon-12
 Relative molecular mass is the sum of the relative atomic masses of all
  the atoms in 1 molecule.
 Relative molecular mass=12 x average mass of one molecule of the
  element/ mass of one atom of carbon-12
         Molar mass vs relative
       atomic/molecular masses
 Same except molar mass has units of g/mol
 Relative atomic mass & relative molecular mass are

Find the molar mass of magnesium carbonate, MgCO3
MgCO3= 24+12+3x16=84g/mol
Find the relative molecular mass of carbon dioxide, CO2.
CO2= 12+2x16=44 (NO UNITS!)
Amount of substance vs mass
More problems
 Find the moles of water molecules present in 54g of
 Moles of water molecules= 54g/18g mol-1=3.0mol
Everything combined!
 Calculate the number of calcium atoms present in
  0.5kg 0f calcium
 Amount of calcium=500g/40g mol-1=12.5mol
 Atoms of calcium=12.5 mol x Avogadro's constant= 12.5
  x 6.02 x 1023= 7.53 × 1024
Everything combined more!
 Calculate the number of carbon and hydrogen atoms and
    the total number of atoms in 22g of propane, C3H8.
   Molar mass of propane, C3H8=(3x12)+(8x1)=44g mol-1
   1 mole of propane therefore has a mass of 44g and contains
    6.02x1023 molecules of propane.
   Amount of propane=22g/44g mol-1= 0.50mol
   Molecules of propane=0.5 x 6.02x1023=3x1023
   Total number of atoms=11x3x1023=3.3x1024
   Total number of carbon atoms=3x3x1023=9x1023
   Total number of hydrogen atoms=8x3x1023=2.4x1024

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