Honors Chemistry
In Class Notes
Mole-Mass and Mole-Volume Relationships
1
Objectives

When you complete this presentation, you will be able to:
o describe how to convert the mass of a substance to the number of moles of a
substance, and moles to mass.
o identify the volume of a quantity of gas at STP (Standard Temperature and
Pressure).
Introduction

How many jelly beans are in the jar?
o How might you approach the problem?

Count each jelly bean

Estimate the volume of each bean

Estimate the mass of each bean

As chemists, we can’t count the number of individual atoms in a reaction (why?).

We rely on other relationships, such as …
o moles → mass and mass → moles
o moles → volume and volume → moles

These relationships allow us to accurately estimate the number of atoms or
molecules involved in a chemical reaction.
The Mole-Mass Relationship

The relationship between the mass of a material and the number of moles of matter
is based on the ________________________ of the matter.
m
M= n
m
or n = M
or m = n  M
o where ____ is molar mass, ____ is mass, and ____ is number of mols.

For example:
o The molar mass of NaCl is 58.5 g/mol
o The mass of 3.00 mol of NaCl is given by
m = n  M = (3.00 molo)(58.3 g/mol) = 176 g

Let’s try Sample Problem 10.5 (page 298)
The Mole: A Measurement of Matter
Sample Problem 10.5
The aluminum satellite dishes are resistant because the aluminum reacts with oxygen in
the air to form a coating of aluminum oxide (Al2O3). This tough, resistant coating prevents
any further corrosion. What is the mass of 9.45 mol of aluminum oxide?
Known:
n = 9.45 mol
M = [(2 × 27.0) + (3 × 16.0)] g/mol = 102.0 g/mol
Unknown:

m = ? g Al2O3
For another example:
o The molar mass of Na2SO4 is 142.1 g/mol
o The mols of 10.0 g of Na2SO4 is given by
n=

m
10.0 g
=
= 7.04  10-2 mol
M
142.1 g/mol
Let’s try Sample Problem 10.6 (page 299)
Sample Problem 10.6
When iron is exposed to air, it corrodes to form red-brown rust. Rust is iron(II)
oxide(Fe2O3). How many mols of iron(II) oxide are contained in 92.2 g of pure Fe2O3?
Known:
m = 92.2 g
M = [(2 × 55.8) + (3 × 16.0)] g/mol = 159.6 g/mol
Unknown:
n = ? mol Fe2O3
Practice Problems:
1. What is the mass of 2.50 mols of hydrogen gas, H2?
2. What is the mass of 0.100 mols of glucose, C6H12O6?
3. What is the mass of 12.0 mols of water, H2O?
4. What is the mass of 0.250 mols of methane gas, CH4?
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Honors Chemistry
In Class Notes
Mole-Mass and Mole-Volume Relationships
3
Practice Problems:
1. How many mols are in 3.25 g of H2?
2. How many mols are in 9.00 g of C6H12O6?
3. How many mols are in 100. g of H2O?
4. How many mols are in 9.60 g of CH4?
The Mole-Volume Relationship

We saw earlier that 1 mol of ____________ or ____________ are not necessarily the same
volume.
o 1 mol of C6H12O6 is a much ____________ volume than 1 mol of H2O.

The story is different with ____________.
o 1 mol of O2 is ________________________________ volume as 1 mol of H2 under the
same conditions.
o 1 mol of O2 is ________________________________ volume as 1 mol of CO2 under the
same conditions.

Why is this?
o In 1811, Amadeo Avogadro proposed that equal ____________ of gases, under
similar conditions, contain the equal ____________________________________.
o This is called ____________________________________.

The individual ________________ of each gas are different sizes and masses.

But, in gases, the distances between the molecules is much ____________ than the
molecule size.

When talking about gases we use the phrase “____________________________________” a lot.
o That is because ________________ and ________________ have a big effect on the
________________ of gases.
o We will find out more about this in the next unit.

To compare different gases, we put them at a ________________________________________.
o This is called “____________.”
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The Mole: A Measurement of Matter

Standard temperature and pressure:
o Standard temperature is ____°C (____________ K).
o Standard pressure is ____ atm (____________ kPa).

Don’t worry about the units right now.

The important thing is that if we say that two gases are at STP, then
they are “under similar conditions.”

At STP, 1 mol of a gas has a volume of ________ L.

The relationship between the ________________ of a gas and the ________________________ of
a gas is given by
V =n  22.4 L
1 mol
or
n = V  1 mol
22.4 L
o where ________ is the volume of the gas in liters (L) and ________ is the amount
of gas in mols

For example
o the volume of 1.25 mols of O2 gas at STP is
V = n  (22.4 L/1 mol) = (1.25 mol)(22.4 L/1 mol) = 28.0 L
o the number of mols of H2 in 67.2 L at STP is
n = V  (1 mol/22.4 L) = (67.2 L)(1 mol/22.4 L) = 3.00 mol

Let’s try Sample Problem 10.7 (page 301).
Sample Problem 10.7
Sulfur dioxide (SO2) is a gas produced by burning coal. It is an air pollutant and one of the
causes of acid rain. Determine the volume, in liters, of 0.60 mol of SO2 gas at STP.
Known:
n = 0.60 mol
Unknown:
V=?L
Honors Chemistry
In Class Notes
Mole-Mass and Mole-Volume Relationships
Practice Problems:
1. What is the volume of 3.25 mols of H2 at STP?
2. What is the volume of 0.250 mols of O2 at STP?
3. What is the volume of 12.5 mols of Cl2 at STP?
4. What is the volume of 0.0100 mols of CH4?
Practice Problems:
1. How many mols of H2 are in 1.00 L at STP?
2. How many mols of O2 are in 50.0 L at STP?
3. How many mols of C2H2 are in 0.250 L at STP?
4. How many mols of F2 are in 11.2 L at STP?

Density and Molar Mass
o The density of matter is mass per unit volume.
ρ = m/V

where ρ = density (g/L), m = mass, and V = volume.
o We can use our mole-mass and mole-volume relationships to determine
density.
M=nM

and
V = n  (22.4 L/1 mol)
Density and Molar Mass
o If we know the molar mass of a gas, then we can calculate its density.
ρ = M  (1 mol/22.4 L)
o If we know the density of a gas, then we can calculate its molar mass.
M = ρ  (22.4 L/1 mol)
o For example, find the density of H2 at STP.
ρ = M  (1 mol/22.4 L) = (2.02 g/mol)(1 mol/22.4 L) = 0.0902 g/L
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The Mole: A Measurement of Matter
6
o For example, find the molar mass of a gas with a density of 3.17 g/L at STP.
M = ρ  (22.4 L/1 mol) = (3.17 g/L)(22.4 L/1 mol) = 71.0 g/mol
Sample Problem 10.8
The density of a gaseous compound containing carbon and oxygen is found to be 1.964 g/L
at STP. What is the molar mass of this compound?
Known:
ρ = 1.964 g/L
Unknown:
M = ? g/mol
Practice Problems:
1. What is the density of F2 at STP?
2. What is the density of CH4 at STP?
3. What is the density of Ne at STP?
4. What is the density of Rn at STP?
Practice Problems:
1. Find the molar mass of a gas with a density of 1.34 g/L at STP.
2. Find the molar mass of a gas with a density of 2.59 g/L at STP.
3. Find the molar mass of a gas with a density of 1.78 g/L at STP.
4. Find the molar mass of a gas with a density of 6.52 g/L at STP.