# Unit 2 Day 2 : Amounts in Chemistry: Mole & Molar

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Day 3: Amounts in Chemistry: Mole &amp; Molar Mass
Materials
Chemistry Learning Goals
Minds On: 25 Min.
Action:
30 Min.
Consolidate/
Debrief: 20 Min
-Students will learn to determine the molar mass of a molecule from its
chemical formula using the periodic table
-Students will learn to convert the mass of a substance to moles, number of
particles and number of atoms
Total = 75 Min.
Assessment
Opportunities
Minds On…
Action!
Consolidate
Debrief



Show students how to determine the molar mass of a substance
Show how to convert molar mass of a substance to mass
Show how to calculate the number of particles from mass
i. Calculating the number of atoms from the mass of
molecules

Solve a scientific question
Problem: How many moles of chalk needed to write your group
name and slogan on the chalkboard?
Hints: The chemical formula for chalk is CaCO3 (calcium
carbonate)Think about the relationship between moles and grams
Materials:
1 piece of chalk
Electronic balance
1 calculator


Application
Concept Practice
Differentiated
Exploration
Reflection
Skill Drill
Blackboard
Place students
in group of 4
Tomorrow mole activity and a mini lab:
o Counting Atoms, Molecules, and Other Entities
Worksheets
Outcome Goals
Calculating the number of particles from mass and the number of atoms from
mass of molecules
Chemistry Grade 12 College: Unit 2 – Quantities in Chemistry (R.Kapoor)
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Calculating number of particles from mass (30min)
So now that we can calculate no. of particles from moles and mass from moles, how do we calculate the no. of particles from
mass!!!
(Show an example)
How many molecules of salt are in a teaspoon (teaspoon = 4.93g)?
Equations: N = n x NA
m=nxM
N=?
n=?
NA = 6.02 x 1023 molecules
mol
m = 4.93g
M NaCl = (Na) + (Cl)
= 22.99g/mol + 35.45g/mol
= 58.44 g/mol
And we know from last lesson: n = m / M
n = 4.93g
58.44g/mol
= 0.08 mol or 8.43 x 10-2 mol
So now that we have mole, we can use the other equation: N = n x N A, to find out the no. of particles:
N = 0.08 mol x 6.02 x 1023 molecules
mol
= 4.81 x 1022 molecules
Therefore, there are 4.81 x 1022 molecules in a teaspoon of salt.
-----------------------------------------------------------------Another example put on the board, where now the students do it in their notebook (5min). And then we take it up as class.
(5min)
How many molecules are in 77.20g of Fe2O3, iron (III) oxide?
N=?
n=?
NA = 6.02 x 1023 molecules
mol
n = 77.20g
159.70g/mol
m = 77.20g
M Fe2O3 = 2(Fe) + 3(O)
= 2 (55.85g/mol) + 3 (16.00g/mol)
= 159.70 g/mol
= 0.48 mol
So now that we have mole, we can use the other equation: N = n x N A, to find out the no. of particles:
N = 0.48 mol x 6.02 x 1023 molecules
mol
= 2.91 x 1023 molecules
Therefore, there are 2.91 x 1023 molecules in 77.2g of Fe2O3
Another example will be put on the board, where now the students do it in their notebook (5min). And then we take it up as
class again. (5min)
What is mass of 3.23 x 1024 molecules of SiO2?
N = 3.23 x 1024 molecules
m=?
Chemistry Grade 12 College: Unit 2 – Quantities in Chemistry (R.Kapoor)
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n=?
NA = 6.02 x 1023 molecules
mol
n = 3.23 x 1024 molecules
6.02 x 1023 molecules/mol
M SiO2 = (Si) + 2(O)
= (28.09g/mol) + 2 (16.00g/mol)
= 60.09g/mol
= 5.37 mol
So now that we have mole, we can use the other equation: m = n x M, to find out the mass:
m = 5.37 mol x 60.09g
= 322.68g
mol
Therefore, 3.23 x 1024 molecules of SiO2 weigh 322.68g.
-----------------------------------------------------------------In the same question above for SiO2, we know that 322.68g has 3.23 x 1024 molecules:
So, how many Silicon atoms are there? And Oxygen atoms?
NSilicon = 3.23 x 1024 molecules x 1 atom
= 3.23 x 1024 atoms of Silicon
molecule
NOxygen = 3.23 x 1024 molecules x 2 atoms
= 6.46 x 1024 atoms of oxygen
molecule
* Use the bicycle analogy: as you the silicon works as the frame and the oxygen is the two wheels. You need one frame to
make bike and two wheels, that’s why the number of bikes will equal to the number of frames.
And the two wheels will be double of the frames or bikes number.
Chemistry Grade 12 College: Unit 2 – Quantities in Chemistry (R.Kapoor)
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Teacher notes: On board (25 min)
Chalk activity:
1. Allow students 10 minutes to figure out how to solve the problem before helping them.
2. Students will eventually work out the problem
3. Procedure for this inquiry:
a. Students should weigh the chalk before – mass of chalk in grams
b. Students write their names and slogan and any other designs they wish on the
chalkboard
c. Students should weigh the chalk after – mass of chalk in grams
d. Students calculate the change in mass by subtracting mass before by mass after:
mass = (mass before – mass after)
e. Students should calculate the formula mass or molar mass for calcium carbonate
(CaCO3) in grams
FW = ________ g/mol
f. Students should calculate moles used to write their names and slogan
mass x 1mol CaCO3____
_____ g CaCO3
= __________ mol of CaCO3
Note: Students should consider using correct significant figure, scientific notation and
correct units.
Chemistry Grade 12 College: Unit 2 – Quantities in Chemistry (R.Kapoor)
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SCH 3U0
Unit 2: Chemical Quantities
Worksheet: Mole and Molar Mass
Name: _________________
Date: _________________
___________________________________________________________________________________________________________________________________________________________________________________________
Worksheet: Mole and Molar Mass
1. How many molecules are in 5.9 mol of NaOH?
2. Find the number of molecules in 2.5 mol of sulfur dioxide.
3. How many atoms are there in 1.45 x 1017 mol of FeCl3? (Hint: you need to find the number of
molecules first.)
4. How many chlorine atoms are present in 1.45 x 1017 mol of FeCl3?
5. A sample contains 4.32 x 1021 molecules of lead (II) iodide. A sample of lead metal contains 2.45
mol of lead atoms. Which sample contains more lead atoms: the compound or the element?
6. How many moles are in 4.45 x 1019 molecules of CO2?
7. Find the molar mass of the following:
a) Zirconium, Zr
b) Sodium carbonate, Na2CO3
c) Hydrogen bromide, HBr
8. For each group, which sample has the largest mass?
a) 5.50 mol of C, 1.32 mol of F2, 2.98 mol of CaCl2.
b) 8.77 mol of H2O, 4.61 mol of NaOH, 10.0 mol of O2.
9. How many moles of ethyne, C2H2 , are in a 13.4 g sample?
10. Sodium chloride can be used to melt snow. How many moles of sodium chloride are in a 15.0 kg
bag?
11. Naphthalene, C10H8, is an ingredient in mothballs. How many molecules of naphthalene are in a
mothball that has 2.000 g of naphthalene? (Hint: Covert to moles first)
12. What is the mass in grams of a sample of Fe2(SO4)3 that contains 3.59 x 1023 sulfate ions, SO42- ?
(This is a challenging question!!)
Chemistry Grade 12 College: Unit 2 – Quantities in Chemistry (R.Kapoor)
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