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# HC hem Ch9 Sec1thru5 by wqh83Zl

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```									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
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
   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