Download Wolfe/Lentz Chapter 6: Chemical Composition Guided Notes 6.1

Wolfe/Lentz
Chapter 6: Chemical Composition
Guided Notes
6.1 Counting by Weight
Jelly bean example:
Average mass=
-------------------------------
To find an average: add ________________ and divide by _____________________
6.2 Atomic Masses: Counting atoms by weighing them
To determine the number of molecules, you must know:
Atomic Mass Unit (amu):
1 amu=
Average Atomic Mass:
Example problem:
1 carbon atom =12.01 amu
Given amu = 3.00 x 1020
3.00 x 1020 amu x 1 carbon atom
= 2.50 x 1019 carbon atoms
12.01 amu
If we know the mass, we can also calculate:
Why isn’t the average atomic mass of any element a whole number?
6.3 The Mole
Samples in which the ratio of the masses is the same as the ratio of the masses of the individual atoms
always contain ________________________________________.
Mole:
Avogadro’s number
A sample of an element with a mass equal to that element’s average atomic mass expressed in grams
contains ___________________________ of atoms.
6.4 Molar Mass
A chemical compound is:
A mol of any compound can be calculated by:
Molar Mass:
The molar mass represents:
Formula Weight
6.5 Percent Composition
Mass Percent:
Mass fraction for a given element = __________________________________________
Mass percentages add up to:
6.6 Formulas of Compounds
The formula of a compound represents:
Ex: CO2 represents:
Empirical Formula
Molecular Formula
6.7 Calculation of Empirical Formulas
To calculate the empirical formula:
Empirical formula is:
Steps for Determining the Empirical Formula of a Compound
Step 1
Step 2
Step 3
Step 4
6.8 Calculation of Molecular Formulas
A molecular formula is always an integer ______________________________________
We can represent empirical formula with:
(Empirical Formula)n =
Is the empirical formula for a compound ever the same as its molecular formula? Explain.
What critical piece of information must be known to determine molecular formula?