Atoms are really, really small…… We can not work with individual atoms or AMU’s in the lab....

The MoleUnit 7: Stoichiometry – Part I

Mrs. Callender

Lesson Essential Questions

What is a mole?

What is a mole used for?

Atoms are really, really small……

We can not work with individual atoms or AMU’s in the lab. Atomic Mass

Unit WHY?Because we can’t see

things that small!

We as scientists work with portions of matter large enough for us to SEE and MASS on a balance using units of……GRAMS

This presents a problem…..

Click icon to add picture

A pile of atoms large enough for us to see

contains billions of

atoms.

Copper (II) Sulfate

So how would we keep track of that many atoms?

Chemists came up with a new unit.

Equivalents or Conversion Factors

1 dozen eggs = 12 eggs

1 rooster = two legs

1 ream of paper = 500 pieces of paper

Equivalents or Conversion Factors

1 mole = 6.02 x 1023

There are EXACTLY 12 grams of Carbon-12 in 1 mole of Carbon-12.

Avogadro’s Number

6.02 x 1023

He studied gases and discovered that no

matter what the gas, there were the same number of molecules

present.Named in honor of Amadeo Avogadro.

1776 - 1856

I did not discover the

number. It was just named after

Units for Avogadro’s Number

1 mole = 6.02 x 1023 (many different units)

For instance:

1 mole of pennies = 6.02 x 1023

pennies.This amount is equivalent to 7 stacks of pennies from the Earth to the moon.

Units for Avogadro’s Number

1 mole Mg= 6.02 x 1023 atoms.

1 mole NaCl= 6.02 x 1023

molecules.1 mole Cl2 = 6.02 x 1023

molecules.1 mole SO4

-2 = 6.02 x 1023 ions.

Calculating Formula Mass

Calculate the formula mass of NaCl.

Na22.98

Cl35.45

22.99 g + 35.45 g = 58.44 g Therefore, 1 mole of NaCl (6.02

x 1023 molecules) has a mass of 58.44 g

Calculate the formula mass of K2O.

K39.09

O15.99

2(39.10) g + 16.00 g = 94.2 g Therefore, 1 mole of K2O (6.02 x

1023 molecules) has a mass of 94.2 g

Calculate the formula mass of (NH4)2SO4.

N14.00

O15.99

942(14.01) g + 8(1.01) g + (32.01) + 4(16.00) g = 132.11 g

Therefore, 1 mole of (NH4)2SO4 (6.02 x 1023 molecules) has a mass of 132.11 g

H1.007

S32.06

Calculating Formula MassCalculate the formula mass of

5 H2O.29

Cu63.54

O15.99

9463.55 g + 32.01g + 4(16.00) g + 5[2(1.01)+16.00] = 249.56 g

H1.007

S32.06

Therefore, 1 mole of CuSO4 5 H2O (6.02 x 1023 molecules)

has a mass of 249.56 g

This type of formula is called a hydrate. It is a salt with water physically attached to it.Example: A salt container with rice intermixed.

Since the water is physically attached how could it be removed?

By heating. When the water is removed the remaining salt is called anhydrous.

Atoms are really, really small…… We can not work with individual atoms or AMU’s in the lab....

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