Moles Activity & Practice
Unit 2 Assignment 6
Name ______________________________ Date _________
Introduction
- When we work with chemical quantities, we use the unit called a mole. This is because we work with
an enormously large number of particles in each chemical reaction experiment and we need to be able
to count them quickly!
- A mole is like a dozen in that it is a unit that represents a set number of particles.
- We can relate 1 mole to the number of particles, which is 6.02×10!" particles
- We can relate 1 mole to the mass of a specific substance. The mass of 1 mole is the molar mass.
- We do not relate the number of particles to the mass of a specific substance directly. We must do this
in two steps using the two relationships involving the mole.
Practice
As we know, 1 dozen = 12 particles and in chemistry, we use Avogadro’s number to define 1 mole.
1 mole = 6.02×1023 particles (you can see why we don’t count them individually!). A ‘particle’ can mean an
atom or a molecule or a formula unit – we’ll learn about molecules and formula units later in the semester.
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Abbreviate mole as mol. Use this equivalence as a set of conversion factors:
and
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1) Calculate moles for each of the following:
a. 2.45 x 1023 atoms of carbon (C)
b. 1921 atoms of bromine (Br)
c. 4.6 x 1020 atoms calcium
d. 8.24 x 1022 apples
2) Calculate the number of particles for each of the following:
a. 1.25 moles of oxygen (O)
c. 0.073 moles of potassium (K)
b. 0.446 moles of lithium (Li)
d. 8.245 moles of apples
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The relationship between moles and mass is called the molar mass. The molar mass is the mass of one
mole of a substance. We get this mass from the periodic table. Remember the atomic mass? That value is the
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value of the molar mass, but with units of grams per mole, or
. For example, the molar mass of carbon is
12.011
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3) Determine the molar mass for each of the following (note: molar mass can be rounded to two digits after
the decimal point):
a. Chlorine (Cl): ____________________
d. Sodium (Na): ____________________
b. Potassium (K): ____________________
e. Silver (Ag): ____________________
c. Beryllium (Be): ____________________
f.
Nickel (Ni): ____________________
Now that you know how to find the molar mass of a substance, you can use the molar mass as a conversion
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factor. For iron, the conversion factor can be used as:
or
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4) Calculate the number of moles equivalent to each of the following:
a. 152.2 grams of iron (Fe)
b. 34 grams of copper (Cu)
5) Calculate the mass of each of the following:
a. 0.743 moles of aluminum
b. 4.2 moles of silicon (Si)
6) Multi-step problems: Use multiple conversion factors: Avogadro’s number and the molar mass.
a. How many grams are there in 3.4 x 1024 atoms of helium (He)?
b. How many atoms are there in 4.25 grams of silver (Ag)?
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