Mole Concept: Grade 9

Grade 9 Quarter 2 Science 9
Mole Concept
mab
Lesson 1: Mole Concept
Introduction:
The mole concept is a convenient method of expressing the amount of a substance. Any measurement can
be broken down into two parts – the numerical magnitude and the units that the magnitude is expressed in. For
example, when the mass of a ball is measured to be 2 kilograms, the magnitude is ‘2’ and the unit is ‘kilogram’.
When dealing with particles at an atomic (or molecular) level, even one gram of a pure element is known to
contain a huge number of atoms. This is where the mole concept is widely used. It primarily focuses on the unit
known as a ‘mole’, which is a count of a very large number of particles.
Reminders:
 Mole is the SI unit used to measure the amount of substance whose number of particles is the same as
the number of atoms of carbon in exactly 12g of Carbon-12
 Avogadro’s number is the number of representative particles in a mole (6.02x10 23)
 Atom is the smallest particle of an element
 Moles can be used to count “representative particles:” atoms, molecules, ions, and formula units.
 The representative particle of an ionic compound is the formula unit.
 The representative particle of a covalent compound is the molecule.
 The representative particle of an element is the atom.
The number 6.02214076 x 1023 is popularly known as the Avogadro constant or Avogadro’s number and is
often denoted by the symbol ‘NA’. The elementary entities that can be represented in moles can be atoms,
molecules, monoatomic/polyatomic ions, and other particles (such as electrons).
For example, one mole of a pure carbon-12 (12C) sample will have a mass of exactly 12 grams and will
contain 6.02214076 x 1023 (NA) number of 12C atoms. The number of moles of a substance in a given pure
sample can be represented by the following formula:
n = N/N A
Where n is the number of moles of the substance (or elementary entity), N is the total
number of elementary entities in the sample, and NA is the Avogadro constant.
Note:
The word “mole” was introduced around the year 1896 by the German chemist Wilhelm Ostwald,
who derived the term from the Latin word moles meaning a ‘heap’ or ‘pile.
Illustration:
To visualize the concept here is a mole of popcorn seeds compared to the salt cube:
Source: www.wired.com/wiredscience/2010/10/how-big-is-a-mole/
The number of moles of a molecule may not always be equal to the number of moles of its constituent
elements. For example, a mole of water contains NA number of H2O molecules. However, each water molecule
contains 2 hydrogen atoms and one oxygen atom. Therefore, one mole of H2O contains 2 moles of hydrogen and one
mole of oxygen.
Sample Problem:
How many molecules are there in 4.0 moles NaCl (Table Salt)?

To answer this question, you have to consider this:
1 mole = 6.02 x 1023 particles

Using the dimensional analysis approach, you will be able to convert the number of
moles to its equivalent amount in the number of particles.
4.0 moles NaCl (table Salt) x6.02 x 1023 molecules of NaCl = 2.41 x 1024 molecules NaCl
1 mole NaCl
Activity 1: Identifying Number of Moles
1 mole = 6.02 × 1023 particles such as atoms, ions, or molecules
1. How many hydrogen ions (H+) are in a mole?

__________________________

2. How many moles of copper are in 6,000,000 atoms of copper?
________________________

3.How many grams are in a sample containing 2.71 x 1024 atoms of iron?
_________________________

4.How many atoms of carbon and sulfur are needed to make one molecule of carbon disulfide (CS2)?
__________________________.

5. How many moles of carbon atoms and sulfur atoms does it take to make one mol of carbon disulfide
(CS2) molecules? __________________________.

Lesson 2: Molar Mass
Introduction:
A mole is a SI unit tomeasure the amount of a substance. For different substances, one mole always
contains 6.02 x 1023 particles and has different masses. Refer to the given table below for the examples.
CHEMICAL NUMBER OF MOLAR MASS

SUBSTANCE
FORMULA PARTICLES (g/mole)
Sodium chloride
NaCl 6.02 x 1023 58.45
( Table salt)
Water H2 O 6.02 x 1023 18.00
Atomic and Molecular Mass
The atomic mass of an element is the mass of one atom of the element expressed in atomic
mass units (amu). It accounts for the abundance of the various isotopes of the element and assigns
an average value to the mass of one atom of the element. For example, the atomic mass of carbon is
12.011 atomic mass units since carbon samples generally contain 98.89% of the carbon-12 isotope,
1.11% of carbon-13, and trace amounts of carbon-14. However, the atomic masses of these isotopes
are different.
The atomic mass of a carbon-12 atom is 12 atomic mass units, but that of a carbon-13 atom is
13 amu. The atomic mass of an element is roughly equal to the sum of all the protons and neutrons
present in its nucleus.
The molecular mass of an element is the sum of the atomic masses of all its constituent
elements. This quantity is also represented in terms of atomic mass units. Therefore, the molecular
mass of water is equal to the sum of the atomic masses of its constituents – hydrogen and oxygen.
The atomic mass of hydrogen is 1.00794 amu and that of oxygen is 15.9994. Since water molecules
contain 2 hydrogen atoms and only one oxygen atom, the molecular mass of H2O is 18.0154 amu.
Molar Mass
The molar mass of a substance is defined as the total mass of one mole of the substance. It is often
represented in terms of ‘grams per mole’ (g/mol). However, the SI unit of this quantity is kg/mol.
Molar mass can be represented by the following formula:

Molar mass of a Substance = (Mass of the Substance in grams)/(Number of Moles)

For example, the molar mass of water is approximately 18.015 g/mol, which is the mass of NA
number of water molecules.

Before we proceed, answer the following activity seriously using the given periodic table.

.
Practice 1:
Element name Mole Molar mass Grams (g)
Sodium 1 or 6.02 x 10 23
Hydrogen 1 or 6.02 x 10 23
Steps to follow to calculate for the molar mass:
1. Identify the elements in the compound.
2. Determine the number of atoms of each element.
3. Write the atomic mass of each element.
4. Write the atomic mass of each element.
5. Get the sum of the product in g/mole.

Summary:
 The mole is defined as the number of atoms contained in exactly 12 grams of carbon-12 (the isotope ).
There are 6.0221415 x 1023 particles in a mole. Remember, a mole is just a number (like dozen) and you
can have a mole of anything.
 The concept of a mole is based on Avogadro’s Hypothesis (equal volumes of all gases at the same
temperature and pressure contained the same number of molecules) and the number of particles in a mole
(6.0221415 x 1023) is commonly referred to as Avogadro’s number (typically rounded to 6.02 x 1023 for
most calculations).
 Because atomic masses, and the number of particles in a mole, are both based on the isotopic atomic
mass of the isotope carbon-12, the mass of any substance expressed in atomic mass units is numerically
equal to the molar mass of the substance in grams per mole. Thus, exactly 12 grams of carbon-12
contains exactly a mole of carbon atoms; likewise, 31.9988 grams of O2 contains 6.02214 x 1023 oxygen
molecules (note, six significant figures)
 To convert the number of moles of a substance into the mass of a substance, you simply need to multiply
(moles x molar mass).
 To convert the mass of a substance into the number of moles, you simply need to divide the mass by the
molar mass.
 To convert the number of moles of a substance into the number of particles of that substance, you simply
need to multiply (moles x Avogadro’s number).
Molar Mass
1. Ag2C2O4
2. HBrO3

Mole Concept: Grade 9

Uploaded by

Copyright:

Available Formats

Mole Concept: Grade 9

Uploaded by

Document Information

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Mole Concept: Grade 9

Uploaded by

Copyright:

Available Formats

Grade 9 Quarter 2 Science 9

1 mole = 6.02 × 1023 particles such as atoms, ions, or molecules

1. How many hydrogen ions (H+) are in a mole?

CHEMICAL NUMBER OF MOLAR MASS

Element name Mole Molar mass Grams (g)

1. Identify the elements in the compound.

2. Determine the number of atoms of each element.

3. Write the atomic mass of each element.

4. Write the atomic mass of each element.

5. Get the sum of the product in g/mole.

You might also like