• Place Moles Wkst #1 on corner of desk for collection.
• Calculate the Molar Mass of Sugar on Bell
Work paper.

Molar Mass of An Element – EASY!!!
• Atomic mass tells the...
– atomic mass units per atom (amu)
– grams per mole (g/mol)
• Round to 2 decimal places

• carbon 12.01 g/mol
• aluminum
26.98 g/mol
• zinc
65.39 g/mol

Molar Mass of A Compound or
Molecule??
• Follow the steps!!!

 1) Write the formula for the compound
 2) List all the elements in the compound
 3) Write how many of each element is in the compound
 4) Write the average atomic mass of each element from the periodic table (round to 2 decimal places)
 5) Multiply average atomic mass by how many atoms are in the compound
 6) Add all totals to get the total Molar Mass
 7) Don’t forget the units!!! (grams/mole)

• water

H
2
O

2(1.01) + 16.00 = 18.02 g/mol
• sodium chloride

NaCl

22.99 + 35.45 = 58.44 g/mol

C
H
O
Find the Molar Mass of Table Sugar (Sucrose)
Formula: C
12
H
22
O
11
Molar mass = _______g/mol
Steps to Calculating MOLAR MASS:
1) Write the formula for the compound
2) List all the elements in the compound
3) Write how many of each element is in the compound
4) Write the average atomic mass of each element from the periodic table (rounded to 2 decimal places)
5) Multiply the average atomic mass by how many atoms are in the compound
6) Don’t forget the units (g/mol).

% Composition
A pure compound always consists of the same elements combined in the same proportions by weight.
Therefore, we can express molecular composition as PERCENT BY WEIGHT .
MgCl
2
25.53% Mg
74.46% Cl

Steps to Calculating PERCENT
COMPOSITION
1) Write the formula for the compound
2) Calculate the MOLAR MASS
3) Divide each element’s mass by the
MOLAR MASSS and multiply by 100 to find that element’s PERCENT
COMPOSITION
4) Don’t forget the units (%)
5) All of the percentages should add up to 100.

Find the Percent Composition of all Elements of Table Sugar
(Sucrose)
Formula: C
12
H
22
O
11
C
H
O
% C
% H
% O
Molar mass = _____g/mol

Exit Ticket Problem:
Percent Composition
What is the percent carbon in C
5
H
8
NO
4
(the glutamic acid used to make MSG monosodium glutamate), a compound used to flavor foods and tenderize meats?
a) 8.22 %C b) 24.3 %C c) 41.1 %C