The Mole Lecture by pengtt

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									Chapter 7

 Chemical
 Quantities
Standards covered in this Lecture


       Standards B, C, and D
         Avogadro’s Number
                          23
              6.02 x 10
Mole: amount of a substance equal
            to Avogadro’s number of
 that       substance.
Ex) mole of molecules
    mole of atoms
    mole of students, etc.
(exploding mole)
Exploding Mole
         # ions,
         atoms        solution
known
                    concentration
grams

         mole

  gas                unknown
volume                grams
         chemical
         formulas
  converting molecules to moles
Ex) How many moles of CO2 equal
            26
    3.3 x 10 molecules of CO2?

3.3 x 1026 molecules     mole
                       6.02 x 1023
                       (molecules)
   = 548 moles CO2
              Molar Mass
     Atomic mass of an element or
    compound expressed in grams.
- used as a custom conversion factor

Ex) molar mass of C = 12.0 g/mol
    molar mass of Na = 23.0 g/mol
    molar mass of Cl = 35.5 g/mol
(NaCl Demo)
gram atomic mass
gram molecular mass
gram formula mass
                      }   Molar Mass


Ex) Calculate the molar mass of CaCO3
      molar mass
  Ca 40.1 x 1= 40.1
  C 12.0 x 1= 12.0
  O3 16.0 x 3 = 48.0
  CaCO3        100.1 g/mol
     converting grams to moles
Ex) Calculate the number of moles in
  5.6g of NaOH.
step 1) find molar mass
          Na     23.0
           O     16.0
           H       1.0
          NaOH 40.0 g/mol
step 2) calculate moles

  5.6 g NaOH        mol
               [   40.0 g
                            ]= 0.14 mol
                                  NaOH




                                    stop
     converting moles to grams
Ex) How many grams are in 3.5 moles
 of ammonium sulfate?
    molar mass (NH4)2SO4
    N2    14.0 x 2 = 28.0
    H8    1.0 x 8 =   8.0
    S     32.1 x 1 = 32.1
    O4 16.0 x 4 = 64.0
    (NH4)2SO4       132.1 g/mol
step 2) calculate grams

3.5 moles (NH4)2SO4
                         [   132.1g
                              mol
                                      ]
    = 462.4 g (NH4)2SO4




acetylene balloon demo
acetylene balloon
     Gas Volume & the Mole
STP:
 Standard Temperature & Pressure

   at sea   0o Celsius   1.0 atmosphere
    level
at STP:
 one mole of any gas    mole
                     or
  22.4 Liters volume    22.4 L
Ex) Convert 0.630 moles of methane
 (at STP) to liters.

0.630 mole CH4           22.4 L
                     [   mole
                                  ]
       = 14.1L CH4


zinc & sulfur demo
zinc & sulfur reaction
      Multiple Step Problems
Ex) How many molecules are in 8.7
  grams of glucose, C6H12O6?
 (grams       moles       molecules)
        molar mass C6H12O6
         C 12.0 x 6 = 72.0
         H 1.0 x 12 = 12.0
         O 16.0 x 6 = 96.0
        C6H12O6      180 g/mol
           [
8.7g glucose mol
            180 g      ][                      ]
                            6.02 x 1023molecules
                                    mol
                  22
     = 2.9 x 10        glucose molecules
 Ex) How many grams are in 4.73 x 1024
  atoms of iron?


4.73 x 1024atoms
                      [ 6.02 x 10
                            mol
                                    23       ][
                                         atoms        ]
                                                  55.8g
                                                  mol

         = 438 g Fe



 ammonium dichromate demo
decomposition of ammonium dichromate
        Percent Composition
   -relative amount of each element in a
                 compound

         grams element
% mass =               x 100
          grams cmpd
Ex) What is the percent of sodium in
sodium chloride? (assume one mole)
% mass Na =    mass Na      x 100
               mass NaCl

     23.0 g/mole
=                      x 100 = 39.3%
  (23.0 + 35.5) g/mole
Ex) Find the percent composition of
aluminum sulfate?
   -find % comp of each element
     molar mass Al2(SO4)3
     Al2   27.0 x 2 = 54.0
     S3    32 x 3 = 96
     O12   16.0 x 12 = 192
                       342 g/mol
       54 g/mol
% Al =            x 100 = 15.8 % Al
       342 g/ mol

    96. g/mol x 100 = 28.1 % S
%S=
    342 g/ mol

    192 g/mol x 100 = 56.1 % O
%O=
    342 g/ mol

  stop
          Empirical Formula
- lowest whole number ratio of atoms in
 a compound
Ex) CH2 is the empirical formula for the
 compound that has the molecular
 formula C6H12.
Ex) H2O is both the empirical formula
 and molecular formula for water
  Calculating Molecular Formulas
amount       %     empirical   molecular
in grams   comp    formula     formula
Ex) What is the empirical formula of a
sample containing 68.8% C, 4.95% H &
26.6% O?
Step 1) Assume a 100 gram sample so:
68.8% C = 68.8 grams C
4.95% H = 4.95 grams H
26.6% O = 26.6 grams O
Step 2) convert grams to moles

68.8 g C
           [   mol
               12.0g]= 5.73 mol C

4.95 g H
           [    mol
                    ]
                1.0g = 4.95 mol H
26.6 g O
           [   mol
               16.0g]= 1.64 mol O
Step 3) Find the mole ratio by dividing
 by the element with the least moles
5.73 mol C   = 3.49 C x 2 = 6.98 ~ 7
1.64 mol
4.95 mol H   = 3.01 H x 2 = 6.02 ~ 6
1.64 mol
1.64 mol O    = 1.00 O x 2 = 2.00 = 2
1.64 mol
 empirical formula: C7H6O2
         Molecular Formulas
Find the molecular formula of a compound
  if its empirical formula is COH2 and its
  molecular mass is 120 g.
emp.form. mass
                        molecular mass
C 12.0           ratio:
                        emp.form.mass
O 16.0
                   120 g
H2 2.0           =       =4
                   30 g
  30.0 g
           C1x4O1x4H2x4 =

								
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