Moles, Mass & Equations

Mole Calculations

How do we measure matter?

● WHAT DO YOU

ALREADY KNOW?

Counting things…

● A term for a certain number of something.

● Brainstorm counting words!

● Dozen = 12

● Pair = 2

● Grand = 1000

● Gross = 144

● A “mole” of something is

6.02 x 1023 of something.

● 602, 000, 000, 000, 000, 000, 000, 000

Essential Questions

● How is a mole used to indirectly count the

number of particles of matter?

● What is a common everyday counting unit to

which the mole can be related?

● How can moles be converted to number of

representative particles and vice versa?

Measuring Matter
Copyright © McGraw-Hill Education

How have you been measuring

matter?

● Did you use a scale to weigh the amount

of salt you used in an experiment?

● Did you take the volume of the amount

of water?

● Did you use a balance to find the mass

of Magnesium you used for a different
experiment?

How do scientists measure

matter?

● Chemists need a convenient method for

accurately counting the number of atoms,
molecules, or formula units of a substance.

● The mole is the SI base unit used to measure

the amount of a substance. (It is like using
the term a dozen eggs)

the Mole

A mole of any
substance is the
amount of the
substance that contains
6.022 x 1023 particles.
A kmol is 6.022 x 1026
particles.

Avogadro's Number

The number of carbon atoms in 12 g of carbon (the

atomic mass of carbon) is 6.022 x 1023.

This is 1 mole of carbon

The number is known as Avogadro's Number and is

designated NA

1 mole contains the atomic mass in grams!

The Mole

● Mole: The amount of a substance that has the

same number of atoms as 12 grams of the
carbon-12 isotope.

● Avogadro’s number: 6.022 x 1023; The number of

atoms in 12 grams of carbon-12.

● Formula Weight is the mass in amu of 1 particle of

a substance. It is numerically the same as the
molar mass.

● The mass of one mole of carbon-12 is 12 grams.

● There are 6.022 x 1023 atoms in one mole of

carbon-12.

Particles

● Atoms for Elements

● Examples: Fe, Hg, Ne, K, C

● Molecules for Covalent Compounds or Elements that exist

in nature as molecules

● Examples: CH4, C3H8OH, F2, SO3

● Ions for Ions

● Examples: Na1+, S2-, PO4

3-

● Formula Units for Ionic Compounds

● Examples: NaCl, K2SO3, Fe2O3

Molar Mass

● The atomic weight on the periodic table is numerically the

same as the molar mass.

● Molar Mass: the mass of one mole of a substance.

● H2O

H: 2 x 1.01 g/mol = 2.02 g/mol
O: 1 x 16.00 g/mol = 16.00 g/mol
2.02 g/mol + 16.00 g/mol = 18.02 g/mol

Complete the Practice Problems

Mass and the Mole

A mole always contains
the same number of
particles; however, moles
of different substances
have different masses.

• The MOLE is the SI

standard unit for measuring
the number of particles

• Avogadro’s Number is the

number of particles in a
mole of substance and is
therefore related to molar &
atomic mass

MAIN IDEA

The Mass of a Mole

One copper atom has a different mass
than 1 carbon atom.

1 mol of copper (6.02 x 1023atoms of
copper) and 1 mol of carbon
(6.02 x 1023atoms of carbon) have
different masses.

Molar Mass

Molar mass is the mass of one mole
of a pure substance (either an
element or a compound).

Molar mass is usually written in
g/mol.

Molar mass of an element is equal
to the atomic mass of the element in
grams/mol except for the diatomic
elements.

Li = 6.941 g /mol

Cr = 51.9961 g/mol

Al = 26.9815 g/mol

H2 = 2.014 g /mol

O2 = 32.00 g/mol

F2 = 37.997 g/mol

Cl2 = 70.91 g/mol

Molar mass is the mass in
grams of one mole of any
pure substance.

The molar mass of any
element equal to its atomic
mass and has the units g/mol.

The Mass of a Mole

MOLE-TO-MASS CONVERSION

Problem : example
Chromium (Cr), a transition element, is a component
of chrome plating. Chrome plating is used on metals
and in steel alloys to control corrosion. Calculate the
mass in grams of 0.0450 mol Cr.

Read carefully and
FOCUS on the
important facts

Don’t be
distracted by
interesting
information..

Using Molar Mass

Moles to mass

Given: 0.0450 moles of Cr.
From the Periodic Table – Molecular Mass of Cr =

52.0g

0.0450 mol Cr x

52.0 𝑔 𝐶𝑟

1 𝑚𝑜𝑙 = 2.34 𝑔 𝐶𝑟

0.0450 moles of chromium
has a mass of 2.34 g.

Does it look right?
The given is less
than a tenth of a
mole is the answer
less than a tenth of
the molecular
mass?

Using Molar Mass

Convert mass to moles with the inverse molar mass conversion factor.

Convert moles to atoms with Avogadro’s number as the conversion factor.

This figure shows the steps to complete conversions between mass and
atoms:

MASS-TO-MOLE CONVERSION

Problem: example 3
Calcium (Ca), the fifth most abundant element on Earth, is
always found combined with other elements because of its
high reactivity. How many moles of calcium are in 525 g Ca?

mass Ca ×1 mol Ca

grams Ca = moles Ca

Remember to stay
FOCUSED on
important facts and
don’t get distracted.

Using Molar Mass : Mass to Moles

Given: 525 g of Ca
From the Periodic Table – Molecular Mass of Ca =

40.1g

525 g Ca x

1 𝑚𝑜𝑙 𝐶𝑎
40.1 𝑔 𝐶𝑎= 13.1 𝑚𝑜𝑙 𝐶𝑎

525 g Ca is equal to 13.1 moles of Ca

Does it look right? 525 g
is more than 10 times the
molecular mass of Ca; 13
moles is more than 10
moles.

Multiple Choice

What is the molar mass of Mg₃N₂?

• 191.6 g/mol

• 76.64 g/mol

• 38.32 g/mol

• 100.95 g/mol

Multiple Choice

The number 6.02 x 10²³ is called...

• Obama's number

• Bohr's number

• Trump's number

• Avogadro's number

Multiple Choice

What is the molar mass of NaCl?

• 58.45g/mol

• 28g/mol

• 12g/mol

• 6.02 x 10²³

Multiple Choice

How many moles of carbon atoms are there in 5g of carbon?

• 60 mol

• 17 mol

• 0.42 mol

• 7 mol

Multiple Choice

The mass of one mole of an element is equal to

• its atomic number from the periodic table, but in amus.

• its atomic mass from the periodic table, but in amus.

• its atomic mass from the periodic table, but in grams.

• its atomic number from the periodic table, but in grams.

Multiple Choice

The molar mass of an element is the mass of one ____ of the element.

• atom

• molecule

• mole

• gram

Multiple Choice

Where do you look to calculate the molar mass?

• avogadros number

• periodic table 

Multiple Choice

What is the molar mass of Mg₃N₂?

• 191.6 g/mol

• 76.64 g/mol

• 38.32 g/mol

• 100.95 g/mol

Multiple Choice

How many moles are there in 12.7g of CaF₂?

• 0.20 mol

• 1,000.76 mol

• 6.14 mol

• 0.16 mol

Multiple Choice

Find the mass in grams of 0.75 moles of magnesium (Mg).

• 32 grams

• 18 grams

• 2.21 x 10 ^23 grams

Multiple Choice

2H₂  +   O₂  →  2H₂O
How many moles of oxygen are consumed if 8 moles H₂ are used?

• 2

• 4

• 6

• 8

Multiple Choice

For the Balanced Reaction: 3 Mg + 1 Fe₂O₃ → 3 MgO + 2 Fe; What is the Ratio of moles of MgO to moles Fe?

• 3mol Mg / 2 mol Fe

• 2 mol Mg/ 3 mol Fe

• 1 mol Fe/ 2 mol Fe

• 3 mol MgO / 2 mol Fe

Multiple Choice

 SiO₂ + 3C → SiC + 2CO
I need to add 8 moles of Carbon to the reaction. How many grams of Carbon should I weigh?

• _{96 g}

• 0.67 g

• 2.67 g

• 48 g

Multiple Choice

2 NaClO₃ (s) --> 2NaCl (s) +3 O₂ (g)  
12.00 moles of NaClO₃ will produce how many grams of O₂?

• 256 g of O₂

• 576 g of O₂

• 288 g O₂

Multiple Choice

At the end of chemical reactions, what is the total mass of the reactants compared to the total mass of the products?

• the product is doubled

• the product is half the mass of the reactants

• the mass is the same

• the mass changes depending on the reaction

Multiple Choice

Balance this equation:
 2Li + Cl₂ → LiCl

• 2Li + Cl₂ → 4LiCl₂

• 2Li + Cl₂ → LiCl₂

• 2Li + Cl₂ → 2LiCl

• 2Li + 2Cl₂ → 2 LiCl₂

Multiple Choice

What is the number before a chemical formula called?
Ex: 2H₂ + O₂ --> 2H₂O

• Coefficient

• Subscript

• Atom

• Equation

Multiple Choice

Is the following equation balanced?
2C₂H₂ + 5O₂ --> 4CO₂ + 2H₂O

• yes

• no

Multiple Choice

Is the following reaction balanced?
NaHCO₃ --> Na₂CO₃ + H₂O + CO₂

• yes

• no

Multiple Choice

Which of the following equations are correctly balanced?

• 12CO₂ +H₂O --> C₆H₁₂O₆ + O₂

• CO₂ + 9H₂O --> C₆H₁₂O₆ + O₂

• CO₂ + H₂O --> 3C₆H₁₂O₆ + O₂

• 6CO₂ + 6H₂O --> C₆H₁₂O₆ + 6O₂

Multiple Choice

For the Balanced Reaction:
3 Mg + 1 Fe₂O₃ → 3 MgO + 2 Fe;
What is the Ratio of moles of Mg to moles Fe?

• 3mol Mg / 2 mol Fe

• 2 mol Mg/ 3 mol Fe

• 1 mol Fe/ 2 mol Fe

• 3 mol MgO / 2 mol Fe

Multiple Choice

How many moles of hydrogen gas are needed to react completely with 2.0 moles of nitrogen gas?

3 H₂(g) + N₂(g) --> 2NH₃(g)

What is the mole ratio of hydrogen gas to nitrogen gas?

• 1:3

• 3:1

• 1:2

• 2:1

Multiple Choice

The ______________ yield is the maximum amount of product possible in a reaction. This determines the amount of product that should be produced in a perfect setting

• Percent

• actual

• stoichiometry

• theoretical

Multiple Choice

7. The amount of product that actually forms when a chemical reaction is carried out in a laboratory is called the _________ yield.

• actual

• theoretical

• percent

Review

Essential Questions

Why can the mass of an atom be related to the mass
of a mole of atoms?

How can the number of moles be converted to the
mass of an element and vice versa?

How can the number of moles be converted to the
number of atoms of an element and vice versa?

Vocabulary
molar mass