What is the Mole?

Hint: Its not a small mammal…

The Mole in Chemistry The mole is a unit of measurement in chemistry. The mole is similar to other counting units such

as 12 eggs equals 1 dozen. One mole of any substance contains 6.02x10^23

number of particles. (Avogadro's Number) Therefore, one mole of eggs would have

602000000000000000000000 eggs. The mole is a great way to count matter without

using really big numbers. This is important for chemistry because there are

millions of particles in small amounts of substances

The Mole in Chemistry (Cont.) The mole is a great way to count matter

without using really big numbers. This is important for chemistry because

there are millions of particles in small amounts of substances

Just 18 mL (or grams) of water contains 6.02x10^23 molecules of water

This presentation will help to explain how we can find out how many moles and molecules are in a given amount of a substance.

A Mole of Carbon

There are 12 grams in one mole of carbon. All of the other elements mole number is relative to that of carbons. Amazingly, there are 6.02x10^23 atoms in each of the samples above.

How to Calculate the Mole A sample of 12 grams of carbon is equal to one

mole. The amount of moles in a substance can be

determined using that substance’s molar mass.

The molar mass is the amount of grams in one mole of a substance.

The molar mass is the average atomic mass for a substance.

Ex. Carbon has an atomic mass of 12 amu so its molar mass is 12 g/mol

Molar Mass The molar mass of an atom, molecule, or

compound is the number of grams in one mole of the substance.

Molar Mass = Grams/mole Ex. Molar Mass of pure Sodium (Na)

Find Sodium on the Periodic Table The molar mass is equal to the atomic mass Therefore, the molar mass is 22.99 or 23.0

grams

Calculating Molar Mass for Compounds For compounds, the molar mass is the

combined total of all the atomic masses for each atom in the compound.

Ex. C6H12O6 There are 6 carbons, 12 hydrogen, and 6

oxygen Carbon has an atomic mass of 12, so we

multiply 12 by 6 for a total of 72. We do the same for hydrogen and oxygen and

add them all together for the molar mass. C: 6(12) = 72, H: 12(1) = 12, O: 6(16) = 96 So, 72+12+96 = 180 grams/mole

You Try!

What is the molar mass of NH3?

A. 14 g B. 17 g C. 4 g D. 25 g

Use the Periodic Table

Try Again Use this other example of how to

calculate molar mass. Try Again

Correct!!! Good Answer! Now learn about

mole conversions.

Mole Conversions

Grams have to be converted to moles before converting to number of particles.

Grams x 1mol/molar mass = Moles Moles x 6.02x10^23/1mol =

Particles

Calculating the Moles in a Given Substance Suppose you were given a graduated cylinder with 18

mL of water in it and you were told to find the number of moles. (Hint: 18 mL of water is equal to 18 grams of water)

First, we need to find the molar mass for water (H2O) using the average (or relative) atomic masses on the periodic table.

2 H @ 1 g each = 2 g 1 O @ 16 g = 16 g 2 g + 16 g = 18 g of water in 1 mole

Second, we set up a conversion factor to convert the grams of water to moles.

18 grams H2O x 1 mole H2O/18 grams H2O (the grams cancel and we are left with moles)

= 1 mole of water

Calculating Number of Particles from Moles

You can convert moles to the number of particles of a substance.

Take the number of moles and multiply it by Avogadro’s Number (6.02x10^23)

For example, we found that 18 grams of water is equal to 1 mole.

1mole water x 6.02x10^23 particles/mole = 6.02x10^23 particles

Let’s Try That Again! Suppose that you have 117 grams of table salt (NaCl).

How many particles of salt are present? First, calculate the molar mass (using the average

atomic masses on the Periodic Table) 1 Na @ 23g = 23g 1 Cl @ 23.5g = 35.5g 23g + 35.5g = 58.5g

Second, convert grams to moles 117g NaCl x 1 mole NaCl/58.5g NaCl = 2 moles NaCl (the

grams cancel and you are left with moles) Third, convert moles to particles (using Avogadro's

Number) 2 mole NaCl x 6.02x10^23 particles NaCl/1 mole NaCl =

1.2x10^24 particles NaCl

Now You Try!

If you were given a 78g sample of LiF, how many moles would be present in the sample? Use the Periodic Table.A. 1 mole B. 2 moles C. 3 moles D. 4 moles

Calculating Molar Masses Using the Periodic Table

•You can find the molar mass of an element by looking at its atomic mass. Here it is located directly under the element symbol and is 107.87.

•To find the atomic mass for a compound you just have to count the number of each element and find the atomic mass for each then add them together.

•For example, AgO3 is

•1 Ag @ 107.87g

•3 O @ 16g = 16x3 = 48g

•107.87g + 48g = 155.87g

•So, there are 155.87g in one mole of AgO3

Not Quite Review the example problem and try

again.

Correct!!! Great Job!

Another Example Problem

How many moles are in 12 grams of NH3?

A. 1.0 B. 2.5 C. .71 D. 1.8

Need the Periodic Table?

Incorrect Please try again.

Yup!!! Good Answer. Now try to

convert moles to particles.

Try This One

How many atoms are present in 2.5 moles of pure sodium? A. 1.5x10^24 B. 1.2x10^23 C. 57.5 D. 135.8

Nope… Try Again!

You’re Right!!! Good Work!

Final Assessment

How many particles (molecules) of glucose (C6H12O6) are present in a 270 gram sample?

A. 1.5 B. 9.03x10^23 C. 6.02x10^23 D. 2

Not Quite

Remember it’s a two step process. You have to convert grams to moles and then moles to particles.

Try Again

Great Job! You have learned about the mole and

mole conversions!