A Chemist’s Dozen

Common MeasuresWe frequently refer to measures casually…

Couple

Few

Dozen

Baker’s Dozen

Ream

LORD

2

3

12

13

500

4

Atoms are REALLY small!!! We can’t work with individual atoms or

atomic mass units in the LAB – Because we can’t see things that small

we work with samples large enough for us to SEE and WEIGH on a balance using units of grams.

This Creates a Problem…

Billions of atoms are hard to keep track of in calculations

A pile of atoms big enough for us to see contains billions of atoms.

A Chemist’s Dozen

It represents a number of ‘things, just like a dozen

In honor of Amedeo Avogadro, Italian chemist (1776-1856)

6.022 x 1023 is referred to as

Avogadro’s Number (NA)

1 mole (unit: mol) = 6.02 x 1023 atoms(symbol: n) (or molecules)

The Mole (n)

This is a HUGE number!!!!

1 mole = 6.02 x 1023 particles, molecules, atoms.

1 dozen eggs = 12 Eggs

1 mole of eggs = 6.02 x 1023 Eggs

How Big is a Mole?

A mole of marbles would cover the entire Earth’s surface 50 MILES DEEP!!!!

How Big is a Mole? If you spent a BILLION DOLLARS

every SECOND, you couldn’t spend a mole of dollar bills in your lifetime!!!

How Big is a Mole? If you were able to count at the rate

of 1 million numbers a second, it would take about 20 billion years to count out one mole.

What are particles?Molecules – covalently

bonded compounds. Usually a non-metal and a non-metal.

The molecule of water is the particle that is counted.

1 mole of water has 6.02 x 1023 molecules/mol.

What are particles?Formula Units– ionically

bonded compounds. Usually a metal and a non-metal

The formula unit of salt is the particle that is counted

1 mole of salt has 6.02 x 1023 formula units/mol

What are particles?Atoms– elemental.Found on the PT of E,

but not part of HOFBrINCl.

The atom of copper is the particle that is counted.

1 mole of copper has 6.02 x 1023 atoms/mol

Pop QuizIdentify the unit for each substance.

a) Methane (CH4)

b) Magnesium chloride

c) Aluminum

d) Butane (C4H10)

e) Hydrogen peroxide

f) Sodium nitrate

g) Calcium

a) moleculeb) F.U.c) atomsd) moleculee) moleculef) F.U.g) atoms

Moles to Particles Calculations

A “dozen” is an easy way to say “12”.

A “mole” is an easy way to say “6.02 x 1023”

Calculation Line

MOLE Particles(molecules F.U. Atoms)

X

÷

Avogadro’s Number

There are 0.50 mol of methane, CH4 in a flask. How many

molecules are present?

N = n x NA

= (0.50 mol)(6.02 x 1023 molecules/mol)

= 3.01 x 1023 molecules

There are 3.01 x 1023 molecules of methane

How many molecules are found in 1.25 mol of CO2?

N = n x NA

= (1.25 mol)(6.02 x 1023 molecules/mol)

= 7.525 x 1023 molecules

There are 7.52 x 1023 molecules of carbon dioxide.

How many moles are found in 5.83 x 1024 molecules of CO2?

n = N/NA

= 5.83 x 1024 molecules 6.02 x 1023 molecules/moln = 9.68 mol

Therefore there are 9.68 mol.

How many moles are found in 3.57 x 1025 atoms of zinc?

n = 3.57 x 1025 atoms 6.02 x 1023 atoms/moln = 59.3 mol

Therefore there are 59.3 mol of zinc.