I N T R O D U C I N G T H E M O L E

CHEMICAL QUANTITY

WHAT DO WE MEAN BY MOLE?

The animal with the weird nose? The popular sauce in Mexican cuisine?

A dark “spot” on a person’s face or body?

THE MOLE WE ARE TALKING ABOUT

• The mole is a counting number (like a dozen)used in chemistry to express amounts of a chemical substance

• It is also referred to as Avogadro’s number

• 6.022 X 1023 or 602200000000000000000000

• A VERY large amount.

1 mole of hockey pucks would equal the mass of the moon!

1 mole of pennies would cover the Earth 1/4 mile deep!

1 mole of basketballs would fill a bag the size of the earth!

EXAMPLES

A dozen eggs is how many eggs?12

A dozen boron atoms is how many boron atoms?12

A mole of eggs would be how many eggs?6.022 X 1023

A mole of boron atoms would be how many boron atoms?

6.022 X 1023

FINDING THE MASS OF ONE MOLE OF AN ATOM OR MOLECULE.

To find out how much one mole weighs for an atom, you can go to the periodic table and find that element’s ____________________________. This is also referred to as an element’s _________________________.

Atomic mass

Molar mass

PRACTICE

What is the mass of one mole of copper?

Answer: 63.55 g

What is the molar mass of lead?

Answer: 207.2 g

WHAT ABOUT COMPOUNDS?

Steps to finding the molar mass of a compound

Step 1: List the elements in the compound and the number of atoms you have for each element.

Step 2: Write the molar mass of each element and multiply it by the number of atoms.

Step 3: Add the masses for each element to get the molar mass(Make sure you are following rules for sig figs)

PRACTICE

WaterFormula: H2O

H: (2)(1.008)+O:(1)(16.00)= 18.02 g/mol

Sodium ChlorideFormula: NaClNa: (1)(22.99)+Cl:(1)(35.45)= 58.44 g/mol

MORE PRACTICE

• sodium bicarbonate• Formula: NaHCO3

• Na: (1)(22.99)+• H: (1)(1.008)+• C (1)(12.01) +• O: (3)(16.00)• = 84.01 g/mol

• sucrose• C12H22O11

• C: (12)(12.01)+• H: (22)(1.008)+• O: (11)(16.00)• =342.30 g/mol

MOLAR CONVERSIONS

1. Write down your given and what you are trying to find

2. Cross out to get what you want

3. Use mole island (p.15 CRM)

4. Significant figures is determined by the given

5. Always include the compound and unit

(remember sig figs)

EXAMPLE

• How many moles of boron are in 25 g of boron?

25 g of B 10.81 g of B

= 2.3 mol of B

1 mol of B

PRACTICE

• How many moles of NaCl are in 100 g of NaCl?

MORE CONVERSIONS

We now can go between mass (grams) and molesHow do we go between moles and number of

particles or vice versa?Remember that Avogadro’s number is the number

of particles in a moleTherefore that will be our conversion factor1 mol = 6.02 X 10 23 atoms, molecules, or

representative particles

CONVERTING NUMBER OF ATOMS TO MOLES

Magnesium is a light metal used in the manufacture of aircrafts, automobile wheels, tools, and garden

furniture. How many moles of magnesium is 1.25 X 1023 atoms of magnesium?

KNOWNS:# of atoms = 1.25 X 1023 atoms Mg

UNKNOWN:Moles of Mg = ?

1.25 X 1023 atoms Mg

2.08 X 10-1 = 0.208 mol Mg

1 mol Mg

6.02 X 1023 atoms Mg

NOW YOU TRY

• How many moles is 2.80 x 1024 atoms of silicon?

YOUR TURN

• How many molecules are in 1.14 mol SO3 ?

• How many moles are in 4.65 X 1024 molecules of NO2 ?

MOLE-VOLUME RELATIONSHIP

Volume of a Gas• Gases are difficult to weigh (mass)

• The volume is effected by temperature and pressure

• Gases must be compared at the same temperature and pressure when finding the amount of moles of gas we have

STP

Standard Temperature and Pressure

• 00 and 1 atmosphere (atm) of pressure

• At STP, 1 mole of any gas occupies 22.4 L

• This is referred to as molar volume1 mole = 22.4L of gas at STP

EXAMPLES

• What is the volume of 4.59 mole of CO2 gas at STP?

4.59 mol of CO2 22.4 L CO2 = 103 L of CO2

1 mol CO2

MORE PRACTICE

• How many moles is 5.67 L of O2 at STP?

What is the volume of 8.8 mol of CH4 gas at STP?