Week 22 Chemistry
Percent Composition, Empirical Formulas, Molecular Formulas
Warm Up: 3 Minutes
Stay in your own seat
Record your Learning
Target
You should be working SILENTLY
A certain bag of M&M’s has 8 blue
candies, 7 red candies, 4 green candies,
and 6 yellow candies. What percentage
of the bag is blue M&M’s?
Do the warm up in OneNote
Agenda

Warm Up [6 minutes]

Pre-Lab/Expectations [7 minutes]

Bubble Gum Lab [18 minutes]

Answer Key [ 4 minutes]

Modeling Tracking [5 minutes]

You Track [10 minutes]

Closing [3 Minutes]
Bubble Gum Lab
Problem
What percentage of Double Bubble Gum is
composed of sugar?
Pre-Lab Question
According to the nutritional manufacturer,
each piece of gum has a mass of 6g with 5g
of sugar. Using this information, what
percent of the gum is sugar by mass?
𝑀𝑎𝑠𝑠 𝑜𝑓 𝑆𝑢𝑔𝑎𝑟
% 𝑆𝑢𝑔𝑎𝑟 =
𝑥 100%
𝑀𝑎𝑠𝑠 𝑜𝑓 𝐺𝑢𝑚
Lab Expectations

Work in assigned groups

Raise your hand if you have a question

No gum should be left on the desks
General information: How to do the lab
1.
Find the mass of your piece of gum before chewing
(include the wrapper)
2.
Chew your gum for ~5 minutes
3.
Find the mass of your piece of gum after chewing
Gum should be placed in wrapper before putting it on mass
balance
4.
Complete analysis and post-lab questions
Bubble Gum Lab

You each need One Piece of Gum and your
Brain

Good Luck!!!
Answer Key
As Mr. Ghosh goes through the answers, highlight the ones you got
wrong
1.
A
12. B
2.
C
13. B
3.
A
14. A
4.
D
15. C
5.
D
16. A
6.
C
17. C
7.
A
18. A
8.
D
19. A
9.
C
20. B
10.
B
21. C
11.
B
Class Averages (and Top Scores)
Period
Top Score
Class Average
1
95%
60%
3
100%
70%
4
90%
79%
5
90%
71%
6
100%
66%
7
95%
64%
What does Tracking Look Like?
Objectives Questions
on the
Exam
Chem.7C
Lewis Dot
Structures
Your
Points
Total Points
Percent
Mastery
Bar Graph
Mastery
85%
 or 
What does Tracking Look Like?
Objectives Questions
on the
Exam
Chem.7C
Lewis Dot
Structures
1-5
Your
Points
Total Points
Percent
Mastery
Bar Graph
Mastery
85%
 or 
What does Tracking Look Like?
Objectives Questions
on the
Exam
Chem.7C
Lewis Dot
Structures
1-5
Your
Points
Total Points
Percent
Mastery
Bar Graph
Mastery
85%
 or 
???
[3 if you
got 3 out
of 5
correct]
What does Tracking Look Like?
Objectives Questions
on the
Exam
Chem.7C
Lewis Dot
Structures
1-5
Your
Points
Total Points
Percent
Mastery
Bar Graph
Mastery
85%
 or 
???
[3 if you
got 3 out
of 5
correct]
5
What does Tracking Look Like?
Objectives Questions
on the
Exam
Chem.7C
Lewis Dot
Structures
1-5
Your
Points
Total Points
Percent
Mastery
Bar Graph
Mastery
85%
 or 
???
[3 if you
got 3 out
of 5
correct]
5
Your points x100
Total points
Percent Mastery
Cathy received 1 point out of 4
possible points. What is
her percent mastery?
25%
Your points x100
Total points
What does Tracking Look Like?
Objectives Questions
on the
Exam
Chem.7C
Lewis Dot
Structures
1-5
Your
Points
Total Points
Percent
Mastery
Bar Graph
Mastery
85%
 or 
???
[3 if you
got 3 out
of 5
correct]
5
Your points x100
Total points
Shade in
your %
mastery
Your Turn
1.
Go to shschem.weebly.com (our class website)
2.
Hover over my page:
Mr. Ghosh  Homework Assignments  ESL (or regular) Chemistry
3.
Under Homework Assignments, there is a new one
labeled “Unit 5 Tracking”
4.
Download (and save) this and fill it out
Closing

Explain the purpose of today’s lab
Warm Up: 4 Minutes
Stay in your own seat
You should be working SILENTLY
1.Log into your computer
2.Go to m.socrative.com
3.Enter room number: 230538
4.Finish all questions
When you are finished, check your grades on PS
Connect
Agenda

Warm Up [7 minutes]

Notes/Examples [15 minutes]

Guided Practice [12 minutes]

Independent Practice [15 minutes]

Closing [3 Minutes]
What is % Composition??
Percent by mass of each
element in a compound
What is % Composition??
Mass of part
% composition by mass =
x 100%
Mass of Whole
Example 1:
A compound contains 2.0g of sodium,
3.5g of oxygen, and 0.5 g of hydrogen.
What is the percent composition of this
compound?
Example 2:
What is the percent composition by
mass of the elements in the
compound, AgNO3?
Guided Practice

Teacher:
1. Will show the problem on the board

Students:
1.
Take 24 seconds to identify your given and unknown.
2.
Take 46 seconds to speak with your shoulder partner
about the problem
3.
Be ready to share when Mr. Ghosh says SWAG
Guided Practice 1:
9.03 g Magnesium combines completely
with 3.48 g Nitrogen to form a
compound. What is the percent
composition of Nitrogen in this
compound?
27.82 % N
Guided Practice 2:
What is the percent composition by mass
of the elements in Mercury (II) Oxide?
92.6% Hg
7.4% O
Guided Practice 3:
What is the percent composition by mass
of the elements in K2CO3?
56.6% K
8.7% C
34.7% O
Independent Practice
Take some time to practice finding the %
composition of the following compounds
Practice makes
Perfect
85%
Closing
How do you find the percent composition of
an element in a compound?
Warm Up: 4 Minutes
Stay in your own seat
Write the Learning
Target
You should be working SILENTLY
1.Log into your computer
2.Go to m.socrative.com
3.Enter room number: 230538
4.Finish all questions
When you are finished, check your grades on PS
Connect
Agenda

Warm Up [7 minutes]

Notes/Examples [15 minutes]

Guided Practice [12 minutes]

Independent Practice [15 minutes]

Closing [3 Minutes]
Goal For Today
Student Given:
Percent
Composition:
79.8% C, 20.2% H
Student Answer:
CH3
Empirical Formulas
Shows the lowest number ratio of
atoms in a compound
empirical formula of glucose =
CH2O
Example 1:
What is the empirical formula for a
chemical compound that is 79.8% C and
20.2% H?
How to Compose the Empirical Formula?
Step 1: Convert
Percent to Grams
Step 2: Convert
Grams to Moles by
dividing grams by
the atomic mass
of each element.
79.8% C and 20.2% H
How to Compose the Empirical Formula?
Step 3:Divide both
molar quantities
by the smallest
mole quantity to
determine the
subscript for each
element in the
formula
79.8% C and 20.2% H
Example 2:
What is the empirical formula for a
compound that is 81.7% Be and 18.3% H?
Guided Practice

Teacher:
1. Will show the problem on the board

Students:
1.
Take 22 seconds to identify the elements
involved.
2.
Take 68 seconds to solve the problem with your
shoulder partner
3.
Be ready to share when Mr. Ghosh says SWAG
Guided Practice 1:
What is the Empirical Formula of a
compound that is 67.6% Hg, 10.8% S, and
21.6 % O by mass?
HgSO4
Guided Practice 2:
What is the Empirical Formula of a
compound that is 88.2 % Oxygen and
11.8% Hydrogen by mass?
H2O
Guided Practice 3:
What is the empirical formula of a
compound that is made from 50%
Cesium and 50% Iodine by mass?
CsI
Independent Practice
85%
Practice makes
Perfect
Closing

What is the empirical formula?

How do you compose the empirical formula?
Warm Up: 4 Minutes
Stay in your own seat
You should be working SILENTLY
1.Log into your computer
2.Go to m.socrative.com
3.Enter room number: 230538
4.Finish all questions
When you are finished, check your grades on PS
Connect
Agenda

Warm Up [7 minutes]

Notes/Examples [15 minutes]

Guided Practice [12 minutes]

Independent Practice [15 minutes]

Closing [3 Minutes]
More Empirical Formulas!!
Writing Empirical Formulas
Most of the time, our mole ratios come out close to a
whole number (~.9, ~.1):
Ratio from Calculator
Examples:
What we assume
1.992
2
16.00412
16
4.962
5
6.071
6
But what if our mole ratio comes out to something like
1.501? What do we do then?
Example 1:
What is the empirical formula for a
chemical compound that is 49.1% Be
and 50.9% N?
Common Decimals/Fractions
When we find a mole ratio that ends up close to a common
decimal/fraction:
X.33
X.5
X.75
X.66
X.25
We must multiply these ratio values by a specific number
Table of Common Decimals/Fractions
Mole Ratio
Multiply all mole ratios
by
Table of Common Decimals/Fractions
Mole Ratio
X.5
Multiply all mole ratios
by
Table of Common Decimals/Fractions
Mole Ratio
X.5
Multiply all mole ratios
by
2
Table of Common Decimals/Fractions
Mole Ratio
X.5
X.33
Multiply all mole ratios
by
2
Table of Common Decimals/Fractions
Mole Ratio
X.5
X.33
Multiply all mole ratios
by
2
3
Table of Common Decimals/Fractions
Mole Ratio
X.5
X.33
X.66
Multiply all mole ratios
by
2
3
Table of Common Decimals/Fractions
Mole Ratio
X.5
X.33
X.66
Multiply all mole ratios
by
2
3
3
Table of Common Decimals/Fractions
Mole Ratio
X.5
X.33
X.66
X.75
Multiply all mole ratios
by
2
3
3
Table of Common Decimals/Fractions
Mole Ratio
X.5
X.33
X.66
X.75
Multiply all mole ratios
by
2
3
3
4
Table of Common Decimals/Fractions
Mole Ratio
X.5
X.33
X.66
X.75
X.25
Multiply all mole ratios
by
2
3
3
4
Table of Common Decimals/Fractions
Mole Ratio
X.5
X.33
X.66
X.75
X.25
Multiply all mole ratios
by
2
3
3
4
4
Example 1:
What is the empirical formula for a
chemical compound that is 49.1% Be
and 50.9% N?
Example 2:
What is the empirical formula of a
compound that is 25.9% Nitrogen and
74.1 % Oxygen by mass?
Guided Practice

Teacher:
1. Will show the problem on the board

Students:
1.
Take 22 seconds to identify the elements
involved.
2.
Take 68 seconds to solve the problem with your
shoulder partner
3.
Be ready to share when Mr. Ghosh says SWAG
Guided Practice 1:
What is the Empirical Formula of a
compound that is 25.9% P and 74.1% Cl?
P2Cl5
Guided Practice 2:
What is the Empirical Formula of a
compound that is 17.4% Nitrogen and
82.6% Fluorine?
N2F7
Guided Practice 3:
What is the Empirical Formula of a
compound that is made from 35.9%
Aluminum and 64.1% Sulfur?
Al2S3
Independent Practice
85%
Practice makes
Perfect
Closing

What is the empirical formula?

How do you compose the empirical formula?
Warm Up: 4 Minutes
Stay in your own seat
Write the Learning
Target
You should be working SILENTLY
1.Log into your computer
2.Go to m.socrative.com
3.Enter room number: 230538
4.Finish all questions
When you are finished, check your grades on PS
Connect
Agenda

Warm Up [6 minutes]

Notes/Examples [11 minutes]

Guided Practice [9 minutes]

Quiz [20 minutes]

Closing [1 Minute]
Goal For Today
Student Given:
Empirical Formula:
CH4O
Molar Mass of
Molecular Formula:
96 g/mol
Student Answer:
Molecular Formula:
C3H12O3
Molecular Formulas
Shows exactly how many of each
atom is in a compound
(unsimplified formula)
Molecular formula of glucose =
C6H12O6
Check Point #1
Is CH2 an empirical or a
molecular formula?
Empirical
Check Point #2
Is S3O6 an empirical or a
molecular formula?
Molecular
(Empirical Formula is SO2)
Example 1:
What is the molecular formula if the
empirical formula is CH4O and the mass
of the whole molecule is 96 g/mol?
How to Compose the Molecular Formula?
Step 1: Find the Mass of Empirical Formula: CH4O
the Empirical Formula
Mass of Molecular
Formula: 96 g/mol
Step 2: Divide the mass
of the Molecular
Formula by the mass
of the Empirical
Formula
How to Compose the Molecular Formula?
Step 3: Multiply the
subscripts in the
empirical formula by
the
answer from step 2.
Empirical Formula:
CH4O
Mass of Molecular
Formula: 96 g/mol
Example 2:
Compose the molecular formula of the
compound whose molar mass is 60.0
g/mol and empirical formula is CH4N.
Guided Practice

Teacher:
1. Will show the problem on the board

Students:
1.
Take 22 seconds to identify the elements
involved.
2.
Take 68 seconds to solve the problem with your
shoulder partner
3.
Be ready to share when Mr. Ghosh says SWAG
Guided Practice 1:
Compose the molecular formula of the
compound whose molar mass is 90 g/mol
and empirical formula is CH2O.
C3H6O3
Guided Practice 2:
Compose the molecular formula of the
compound whose molar mass is 62 g/mol
and empirical formula is CH3O.
C2H6O2
Independent Practice
85%
Practice makes
Perfect
Material Covered on Quiz
 Mole
Calculations (1 and 2 step)
 Percent
Composition
 Empirical
Formulas
Goal

To demonstrate mastery, we are shooting for
Check Point
What is your goal for this quiz?
Expectations for Quiz
Clear your desk of everything except a....
1.
Writing Utensil
2.
Calculator
Periodic Table is provided to you
Expectations

Students will keep eyes on own paper


Cheating will result in an automatic ZERO
Students will remain SILENT for the duration of the quiz
Good Luck!!
Closing

How was your quiz?

What topics do you feel you still need review on?