This document discusses molar mass, percentage composition, and their importance in chemistry. It defines molar mass as the mass of one mole of an element or compound expressed in grams. Percentage composition is calculated by taking the mass of an element divided by the total mass of a compound and multiplying by 100. The document provides examples of calculating molar mass and percentage composition of compounds such as Al(OH)3 and acetic acid. It emphasizes the importance of these concepts for understanding chemical formulas, reactions, and their application to health guidelines during the COVID-19 pandemic.

1. Molar Mass and
Percentage Composition
Jennifer C. Valdez

2. LEARNING OBJECTIVES
• explain the concept in determining the molar
mass and percentage composition
• value the importance of knowing percent
composition
• connect the concept of lessons in our dietary
health guidelines amidst of pandemic
• calculate the molar mass and percent
composition
Learning Objectives

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4. • Let’s Recharge!

5. Law Of Definite Proportions
states that a chemically pure
substance always contains
the same set of elements
combined together in a
definite proportion by
weight.

6. Molar Mass
(Atomic Mass)

7. Molar Mass
The molar mass:
• is the mass of one
mole of an element
or compound
• is the Atomic Mass
expressed in grams
(found on the
periodic table!)

8. Product B
• Feature 1
• Feature 2
• Feature 3
Molar (Atomic) Mass
from Periodic Table
Molar mass is the
atomic mass
(AMU) expressed
in grams…
This Mass is
located below the
Element Symbol
on the periodic
table

9. Percent composition of the
Compound
the percent by mass of an
element in a compound is the
mass in grams of the
element divided by the mass
in grams of the compound
multiplied by 100%.

10. Percent composition of the
Compound
% by mass =mass of the compound
mass of the element
X 100
formula:

11. Product B
Step 1. List down the atoms involved in the formula which are
represented by chemical symbol. Write this in downward
manner in the first column.
Al(OH)3
Atom
Number of atoms Mass Number Total Mass number
of each atom
Al
1 27.0 g 27.0 g
O
3 16.0 g 48.0 g
H
3 1.0 g 3.0 g
78.0 g/mol

12. Product B
Step 2. Determine the number of atoms in the formula. Write
this in the second column. Consider the subscript which is
written outside the parenthesis
Al(OH)3
Atom Number of
atoms
Mass Number Total Mass number
of each atom
Al 1
27.0 g 27.0 g
O 3
16.0 g 48.0 g
H 3
1.0 g 3.0 g
78.0 g/mol

13. Product B
Step 3. Write the mass number of each element in the third
column
Al(OH)3
Atom Number of
atoms
Mass Number Total Mass number of each
atom
Al 1 27.0 g
27.0 g
O 3 16.0 g
48.0 g
H 3 1.0 g
3.0 g
78.0 g/mol

14. Product B
Step 4. Multiply the number of each atom to its mass number to
determine the total mass number of each atom. Write this in the
fourth column.
Al(OH)3
Atom Number of
atoms
Mass Number
Total Mass number
of each atom
Al 1 27.0 g 27.0 g
O 3 16.0 g 48.0 g
H 3 1.0 g 3.0 g
Total molar mass of 78.0 g/mol
Al(OH)3

15. % by mass =mass of the compound
mass of the element
X 100
% by Al = 78.0 g
27 g
X 100 = 34.6 %
% by O = 78.0 g
16 g
X 100 = 61.5 %
% by H = 78.0 g
1.0 g
X 100 = 3.8 %

16. Product B
. One of the products of La Union is vinegar
which is locally produce in the Naguilian and
Aringay. The vinegar is actually a solution that is
made of 4-8% of acetic acid (C2H4O2) that is
dissolved in water and other substances that
give vinegar its flavor depending on its type.
Calculate the percentage composition of acetic
acid (C2H4O2).
.

17. Product B
C: 2 x 12.0 = 24
H: 4 x 1.0 = 4
O: 2 x 16.0 = 32
60 g /mole
C2H4O2

18. % by mass =mass of the compound
mass of the element
X 100
% by C = ______g
g
X 100 = ____ %
% by H = ______ g
g
X 100 = ____ %
% by O= _____ g
g
X 100 = ____%
C2H4O2

19. Product B
Questions:
1. Why is percent composition important?
2. How do you calculate molar mass and percent
composition?
3. What is the law of definite proportion and
composition?
4. How do we apply this lesson in our current
situations of Covid 19 pandemic?
5. Why is healthy eating important for the
immune system, especially during the COVID-19
pandemic?

20. Product B
Assignment:
Directions: Browse the internet and search for
the content of your favorite food. Look for the
RENI (Recommended Energy and Nutrients
Intakes) . You may present through powerpoint
and send it on link.
My favorite food,
________________________________________

21. Product B
Questions:
1. How much is one serving of your favorite
food?
2. How many calories are in one serving of your
favorite food?
3. How many calories from fat are in one serving
of your favorite food?
4. Find the percent of calories from fat in your
favorite food?

22. Product B
https://docs.google.com/spreadsheets/d/1-
mNK739-
ABH9K3b6D2BFTW1_qS8kyMEJ/edit?fbclid=IwA
R0OYMtjzfXOr9DlfLUnn8vH1uPuoj37CPJeJlxMd
V97WTt3_ZCXnTVQvx0#gid=1275597239

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