Goldberg Chapt 7- Formula Calculations p. 183
Objectives (those in italics to be covered in General Chemistry)
To calculate a formula mass
To calculate the percent composition by mass from the formula of a compound
To use the mole to make calculations
To determine the empirical formula
To determine the molecular formula
1. Formula Masses
Formula mass or formula weight- the sum of the atomic masses of all the atoms in the formula unit.
Treat the formula like an algebra expression. The mass unit for individual atoms or molecules is amu.
Example start inside parentheses multiply each atom's mass by its subscript get the sum inside parentheses multiply by subscript that follows parentheses add mass of additional element(s)
= 193.7 amu
2. Percent Composition (by mass)
Apply the formula-
% x = mass of x / total mass * 100%
% Ni = 58.7 amu / 193.7 amu * 100% = 30.3%
%Cl = 71.0 amu / 193.7 amu * 100% = 36.7%
%O = 64.0 amu/ 193.7 amu * 100% = 33.0%
30.3% + 36.7% + 33.0 = 100%
Hint: always check to see that the total is 100%
and you can't miss one of these.
|
National Mole Day Foundation, Inc. |
| 3. The Mole | How many concepts have their own holiday and professional organization? |
| "All about mole calculations" | http://misterguch.brinkster.net/molecalculations.html |
The mole is the fundamental measure of quantity to substance.
AKA gram molecular weight, you get it by using the unit gram for the formula mass calculated in part 1 above.
One mole of a
substance contains 6.02 * 1023
particles of that substance.
Homework p 200
1, 2, 4, 5, 10, 14, 17, 19, 22- 25, 29, 31, 36, 47, 50a, 51, 56, 65
for classroom discussion #85
last revised March 16, 2004