STOICHIOMETRY:
Part I
Jessa Loraine M. Ramos, RChE
Special Science Teacher I
PRAYER
“I will continue,
O my God, to do
all my actions
for the love of
you.”
Attendance
Check
QUIZ!
Chemical nomenclature and
formula writing
Stoichiometry
“chemical stoichiometry” – area of
study which deals with the quantities
of materials consumed and produced
in chemical reactions.
Contents of the Lesson
01
03
Atomic Mass
Review relative atomic
mass
Percent
Composition
Calculations for
percent composition of
compounds
02
04
The Mole and Molar Mass
Avogadro’s Number, molar mass
calculations and mass to mole
conversion and vice versa
Empirical and Molecular
Formulas
Describe the topic of
the section here
01
Atomic Mass
Review relative atomic mass
of elements
Mass Spectrometer
Review Problem- Atomic weight
Potassium, a metal that is highly reactive in water,
has three isotopes, K-39, K-40, and K-41. Given the
atomic masses and abundances of the three
isotopes, calculate the average atomic mass of
potassium.
ISOTOPE
ATOMIC MASS
% ABUNDANCE
K-39
38.9637 amu
93.26%
K-40
39.9640 amu
0.01%
K-41
40.9618 amu
6.73%
Got
questions?
02
The Mole and
Molar Mass
Avogadro’s Number, molar mass
calculations and mass-to-mole
conversions and vice versa
Mole
mol, SI system base
unit for the amount of
substance
One mole of something consists of 6.022 x
1023 units of that substance
For Atoms
1 mol Ar = 6.022 x 1023 Ar atoms
For molecules
1 mol H2O = 6.022 x 1023 H2O molecules
For ions
1 mol Na+ = 6.022 x 1023 Na+ ions
For ionic
compounds
1 mol NaCl = 6.022 x 1023 NaCl formula units
For other
particles
1 mol e- = 6.022 x 1023 e- particles
One mole of something consists of 6.022 x
1023 units of that substance
Determining Moles of Atoms
Sample Problem 1:
Aluminum (Al) is a metal with high strength-to-mass
ratio and a high resistance to corrosion; thus it is often
used for structural purposes. Compute the number of
atoms in a sample containing 0.371 mol of Aluminum
atoms.
Determining Moles of Atoms
SOL’N:
Got
questions?
Counting Atoms
Counting Atoms
Molar Mass


The mass that an atom, or
any substance, has in 1 mole
Measured in gram per mole
(g/mol)
Molar Mass
The unit for the molar
mass is gram per
mole (g/mol). Its
value is the same as
the value of the
atomic mass in
amu.
Molar Mass
For substances
consisting of more than
one atom, the molar
mass is the sum of all
the molar masses of all
atoms present.
Molar Mass Calculations
Sample Problem 2:
Calculate the
molar mass of
elemental
nitrogen, N2
SOL’N:
MMN2 = 2 x 14.01 g/mol
𝐌𝐌𝐍𝟐 = 28.02 g/mol
Got
questions?
YOUR
TURN!
Molar Mass Calculations
Sample Problem 3:
Calculate the molar mass of sodium
bicarbonate.
Ans: 84.01 g/mol
Molar Mass Calculations
Sample Problem 4:
Calculate the molar mass of Ca3(PO4)2.
Ans: 310.18 g/mol
Mass to mole
conversion and
vice versa
Got
questions?
🧠 RECALL
Unit conversions and
use of conversion
factors or unit factors
🧠 RECALL
Mass to mole calculations, vice versa

The molar mass shows the relationship between
the mass and the number of moles in a
substance.

The molar mass can serve as the unit factor for
converting the mass to the number of moles or
vice versa.
Sample Problem 5

What is the mass, in grams, of 0.0245 mol
of Uranium, U?
Sample Problem 6

How many grams are there in a 2.18-mol
sample of KCl?
Sample Problem 6
Mass to mole calculations, vice versa
Got
questions?
YOUR
TURN!
Exercises


How many moles are there in
21.47 g of Zn?
How many moles are there in
3.18 g of AlCl3?
Sample Problem 7
Sample Problem 8

What is the mass of 7.645 x 1021 CaBr2
formula units?
Sample Problem 8
Sample Problem 9
Mass to mole calculations, vice versa
Got
questions?
YOUR
TURN!
Marathon Problems


Compute the number of moles
and atoms in a sample
containing 7.00 g of K.
Compute for the number of
moles and mass of 2.23x1023
atoms of Al.
Marathon Problems! 🧠

What is the (a) mass of 1 mol of ammonia
in grams? (b) How many molecules are
present in 1 mol of ammonia?

Ans. A) 17.04 g, B) 6.022x1023 molecules
Marathon Problems! 🧠

Cobalt (Co) is a metal that is added to
steel to improve its resistance to corrosion.
Calculate both the number of moles in a
sample of cobalt containing 5.00 x 1020
atoms and the mass of the sample.

Ans. 8.30x10-4 mol Co, 4.89x10-2 g Co
03
Percent Composition
Calculations for percent
composition of compounds
Percent Composition
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑋 𝑖𝑛 1 𝑚𝑜𝑙 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑
%𝑋 =
𝑥100%
𝑚𝑎𝑠𝑠 𝑜𝑓 1 𝑚𝑜𝑙 𝑜𝑓 𝑡ℎ𝑒 𝑐𝑜𝑚𝑝𝑜𝑢𝑛𝑑
Example 1
Example 1
Example 2
Example 2
Got
questions?
YOUR
TURN!
Problem 1
Exercises
1. Determine the percent composition of
each element in CH4Cl3F
2. Calculate the mass percent composition
of every element in CO2
Got
questions?
Empirical Formula
 the simplest, whole-number ratio of atoms in a
molecule
 can
be determined from percent composition
or combining masses
 Example:
CH2O is the empirical formula of
C6H12O6 (glucose)
Sample Problem 10

Cyclohexene is made up of 87.73% C and
12.27% H. Determine the empirical mass
of cyclohexene.
Sample Problem 10
Sample Problem 10
Sample Problem 10
Sample Problem 11

A nitrogen oxide molecule consists of
25.9% N and 74.1% O. What is the
empirical formula for this compound?
Sample Problem 11
Sample Problem 11
Sample Problem 11
Got
questions?
YOUR
TURN!
Exercises
1. A sample contains 13.5 g Ca, 10.8 g O,
and 0.675 g H. What is the empirical
formula of the compound?
2. Nutrasweet is 57% C, 6.16% H, 9.52%N,
and 27.18% O. Find the empirical formula
of Nutrasweet.
Molecular
Formula

a multiple of the empirical formula; the
chemical formula that gives the actual
number of atoms of every element in a
compound

Example: C6H6 is the molecular formula
of Benzene
Sample Problem 12

A compound with empirical formula CH
is found to have a molecular mass of
104.14 g/mol. Determine the molecular
formula of the compound.
Sample Problem 12
Sample Problem 12
Sample Problem 12
Sample Problem 13

A solid has empirical formula N2O5. An
experiment was done to determine its
molar mass, and a value of 108.7 g/mol
was obtained. What is the molecular
formula of the solid?
Sample Problem 13
Sample Problem 13
Sample Problem 13
YOUR
TURN!
Exercises
1. Determine the empirical and molecular
formulas for a compound that gives the
following percentages on analysis (in mass
percents):
71.65% Cl
24.27%C
4.07% H
The molar mass is known to be 98.96 g/mol.
Exercises
2. A white powder is analyzed and found to
contain 43.64% phosphorus and 56.36%
oxygen by mass. The compound has a
molar mass of 283.88 g/mol. What are the
compound’s empirical and molecular
formulas?
Got
questions?
“
”
Thanks!
Do you have any questions?
jessaLoraine.ramos@deped.gov.ph
Jessa Loraine M. Ramos
Stay safe and God bless,
everyone!
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