A Chemist’s Dozen

Today you will only need to copy slides that have a TEAL

background

Common Measures

We frequently refer to measures casually…

Couple

Few

Dozen

Baker’s Dozen

Ream

2

3

12

13

500

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)

Definition of a mole: # of atoms in exactly 12g of Carbon-12

6.022 x 1023 is referred to as Avogadro’s Number (NA)

1 mole (symbol: mol) = 6.02 x 1023 atoms(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.

Pop Quiz

1 dozen Mg atoms =

1 mole Mg atoms =

1 mole Mg(OH)2 =

1 mole O2 =

12 Mg atoms

6.02 x 1023 Mg atoms

6.02 x 1023 Mg(OH)2 molecules

6.02 x 1023 O2 molecules

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”

There are 268 donuts. How many dozens are present?

• N = number = 268 donuts• D = ? Dozens• ND= 12 donuts per dozenD = N = 268 donuts ND 12 donuts/dozen

= 22.333 dozensThere are 22 dozens of donuts

N

D ND

There are 2.46 x 1024 donuts. How many moles are present?

• N = number = 2.46 x 1024

• n = moles = ?• NA= Avogadro’s number = 6.02 x 1023

n = N = 2.46x 1024 donuts

NA 6.02 x 1023 donuts/mol

= 4.0863787 molThere are 4.09 mol of donuts

NA

N

n

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

• n = 0.50 mol

• NA= 6.02 x 1023 molecules/mol

• N = molecules =?N = n x NA

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

= 3.01 x 1023 moleculesThere are 3.01 x 1023 molecules of methane

In the same sample of methane, determine how many atoms of H

are present• In 1 molecule of CH4, there are 4

hydrogen atoms4 hydrogen = x

x = 1.20 x 1024 atoms of H

*Note* Covalent compounds are composed of molecules. Ionic compounds are composed of formula units

______________ ____________________

1 molecule CH4 3.01 x 1023 molecules

How many molecules are found in 1.25 mol of CO2?

• n = 1.25 mol

• NA= 6.02 x 1023 molecules/mol

• N = molecules =?N = n x NA

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

= 7.525 x 1023 moleculesThere are 7.52 x 1023 molecules of methane

How many atoms are found in 1.25 mol of CO2?

• n = 1.25 mol• NA= 6.02 x 1023 molecules/mol• N = molecules =?N = n x NA

= (1.25 mol)(6.02 x 1023 molecules/mol) = 7.525 x 1023 molecules7.525 x 1023 X 3 atoms = 2.258 x 1024

atoms1 molecule

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

• n = ?

• NA= 6.02 x 1023 molecules/mol

• N = 5.83 x 1024 molecules

• n = N/NA

= 5.83 x 1024 molecules / 6.02 x 1023

molecules

n = 9.68 mol