Name: ______________________________
The Mole , etc. Honors Chemistry
Calculating the Mass of Atoms:
____________________ was used as the standard for relative mass
Symbol for atomic mass units:
Calculating Formula Weight:
Formula Weight 
Example: Formula weight of NaOH
More Examples:
The MOLE = ____________________________________ representative particles
**A representative particle could be:
Molar Mass (aka Molecular Weight):
Units 
Ex: What is the mass of one mole of aluminum:
Practice:
What is the mass of 2.3 moles of sulfur?
Example:
Given: GRAMS
Unknown: # OF MOLES
How many moles are in 412 grams of CaSO4
How many grams are in 2.4 moles of NaCl
How many moles are in 77.4 g of NaCO3
How many moles are in 3.45E4 g of copper (II) oxide?
What is the mass of 16 moles of Pt?
What is the mass of 22 moles of NO?
Percent Composition
The percent by mass of an element in a compound is the _______________________________________
divided by the _____________________________________________________, multiplied by 100%
EQUATION:
Calculating Percent Composition from Mass Data:
When a 13.60 g sample of a compound containing only magnesium and oxygen is completely
decomposed, 5.40 g of oxygen is obtained. What is the percent composition of this compound?
A compound is formed when 9.03 g Mg combines completely with 3.48 g N. What is the percent
composition of this compound?
Calculating Percent Composition From Chemical Formula:
Example: Propane (C3H8) is one of the compounds obtained from petroleum. Calculate the percent
composition of propane.
Calculate the percent nitrogen in these common fertilizers:
a. NH3
b. NH4NO3
Using Percent Composition as a Conversion Factor:
How:
Example: How much carbon & hydrogen are in 82.0 g of propane?
Recall: what were the percentages of C & H in propane?
So…in a 100g sample of propane, how much carbon & hydrogen would there be?
Calculate mass of C in 82 g of propane:
Calculate mass of H in 82 g of propane:
Determining Chemical Formulas:
EMPIRICAL FORMULA (simplest formula):
To find the empirical formula:
1. Determine the composition by mass – set the 100% to grams. Make each element’s percentage
equal to grams.
2. Determine the composition in moles – divide each number of grams found in #1 above by the
atomic mass of the element.
3. Find the smallest whole-number ratio of atoms – Divide by the smallest # of moles found in #2
above.
Example: Analysis shows a compound to contain 26.56% potassium, 35.41% chromium, and 38.03%
oxygen. Find the simplest formula of this compound:
Example: A compound is found to contain 63.52% iron and 36.48% sulfur. Find the empirical
formula:
Determining MOLECULAR FORMULA:
To find molecular formula for a compound, we need to know the correct _______________________
of the substance.
To determine molecular formula, we ___________________________________________________
__________________________________________________________________________, this
gives us a whole number, which we ___________________ all of the atoms in the simplest formula
by to get the molecular formula.
Example: Determine the molecular formula of a compound having a simplest formula of CH and a
formula mass of 78.110 amu.
A sample of a compound with a formula mass of 34.00 amu is found to consist of .44 g of hydrogen and
6.92 g of oxygen. Find its molecular formula.