Practice Homework 22: Molar Mass Calculations
Definitions/Helpful Info

Molar mass is the mass of substance per 1 mole of substance

MM =

Remember: Regardless of sigfig rules, I want two digits after the decimal point for any molar mass
calculation. What goes in front of the decimal point is irrelevant. The following MM values are examples:
mass
mole

58.27 g/mol

142.41 g/mol

1217.33 g/mol (yes, there are really molar mass values this large, even though it’s uncommon.)
Instructions

Remember: This assignment is not due.

In these examples, show your work. (I will do two sample solutions in the answer key to show you how I
would like your work shown.)

In the future, you will only need to show your work for calculating molar mass when you are asked to do
so.
Questions




Calculate the molar mass of the following compounds. Show your work.
Answers (not solutions) are on the next page.
An asterisk indicates that the solution is included, as well as the answer.
Challenging Problems: Questions 5 and 6
1)
H2O
2)
NaCl
3)
NH3
4)
CO2
5)*
(NH4)2SO4
6)
Al(C2H3O2)3
7)
P4O6
8)
C20H25O30
9)
CoCl6
10)
C8H10N4O2
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Answers
1)
H2O
18.02 g/mol H2O
2)
NaCl
58.44 g/mol NaCl
3)
NH3
17.03 g/mol NH3
4)
CO2
44.01 g/mol CO2
* Solution to Question 5
g/mol
g/mol
2×N

2
×
14.01 
28.02
8×H

8
×
1.01 
8.08
1×S

1
×
32.07 
32.07
4×O

4
×
16.00 
+ 64.00
132.17 g/mol (NH4)2SO4
OR
(2 × N) + (8 × H) + (1 × S) + (4 × O)
=
(2 × 14.01 g/mol) + (8 × 1.01 g/mol) + (32.07 g/mol) + (4 × 16.00 g/mol)
=
28.02 g/mol + 8.08 g/mol + 32.07 g/mol + 64.00 g/mol
=
132.17 g/mol (NH4)2SO4
6)
Al(C2H3O2)3
204.13 g/mol Al(C2H3O2)3
7)
P4O6
224.38 g/mol P4O6
8)
C20H25O30
745.45 g/mol C20H25O30
9)
CoCl6
271.63 g/mol CoCl6
10)
C8H10N4O2
194.22 g/mol C8H10N4O2
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