Your Federal Quarterly Tax Payments are due April 15th Get Help Now >>

HC hem Ch9 Sec1thru5 by wqh83Zl

VIEWS: 0 PAGES: 13

									Chapter 9

Sections:
9.1 Formula Weight and Molecular Weight
9.2 Moles and Molar Masses
9.3 Composition Calculations
9.4 Mass and Mole Conversions
9.5 Calculations with Avogadro’s Number
Formula Weight vs. Molecular
Weight
   Formula Weight = sum of the average
    atomic masses of all the atoms represented
    in a formula for any compound. (amu)
     Example: KClO3
    39.10 + 35.45 + 3(16.00) =122.55amu

   Molecular Weight = sum of the average
    atomic masses of all the atoms represented
    in a molecule (not ionic).
     Example: CO2
    12.01 + 2(15.99) = 43.99amu
Molar Mass
   Mass of one mole of atoms (g)
   Example:
       One Ca atom has a mass of 40.08amu
       One mole of Ca atoms has mass of
       40.08 grams
   Molar mass of a compound is the same
    number as the formula weight, just
    change the units to grams instead of
    amu’s.
More examples of molar mass:
   H2SO4          2(1.008) + 32.07
                    + 4(16.00)
                    = 98.09g
   MgCl2          24.30 + 2(35.45)
                    = 95.20g
                   2(26.98) +
   Al2(SO4)3       3(32.07) +
                    12(16.00)
                    = 342.17g
Percent Composition

   The percent by mass of each
    element in a compound
   Steps to solve:
       1. Calculate the molar mass of the
        compound
       2. Divide the mass of each element by
        the total molar mass of the compound
       3. Multiply by 100 to get %
Find the percent composition of silver
sulfate.

 Ag2SO4
2xAg 2 x 107.9 = 215.8gAg
1xS   1 x 32.07 = 32.07gS
4xO   4 x 16.00 = 64.0gO
           Total = 311.87g Ag2SO4
%Ag = 215.8/311.87 x 100 = 69.20% Ag
%S = 32.07/311.87 x 100 = 10.28% S
%O = 64.00g/311.87 x 100 = 20.52% O
Mass and Mole Conversions

   How many moles of formula units
    are in 190.4 grams of MgCl2?
   Solution:
    190.4g MgCl2 X ______

    190.4g MgCl2 X 1mol MgCl2
                    95.2g MgCl2
    = 2 mol MgCl2
What is the mass of 2.50 moles of O2?

   Solution:
    2.50 mol O2   X   _______

    2.50 mol O2 x 32.0g O2 =
                  1 mol O2
    = 80.0g O2
How many molecules of H2SO4 are
there in 25.0 grams of H2SO4?

25.0 g H2SO4   X   __________   X   ___________

25.0 g H2SO4   X   1 mol H2SO4   X 6.02 x 10
                                            23 molec

                   98.086 g H2SO4     1 mol H2SO4


  = 1.53 x 1023 molecules H2SO4
A Comparison of One Mole of Two
Different Compounds
   1 mole of CO2              1 mole of NaNO3
    (covalent molecule)         (ionic compound) has a
    has a mass of 44.0 g        mass of 85.0 g and
    and contains:               contains:

   6.022 x 1023               6.022 x 1023 formula
    molecules made up of        units made up of
   6.022 x 1023 atoms of      6.022 x 1023 Na+ ions
    carbon and                  and
   2(6.022 x 1023) atoms      6.022 x 1023 NO3- ions
    of oxygen
Determine the mass of 1 molecule
of CO2.

   Solution:
Number of Unit Particles in a
Given Mass


Homework

   Read pages 249-261
   Do page 271-272 #2 -16 even and
    20, 22, 26
   Do page 272-273 #28 – 40 even
    and 44

								
To top