 # Moles, Avogadro’s Number and Molar Mass

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Moles, Avogadro’s Number and Molar Mass
Converting moles to molecules, atoms, and particles

Can anyone define the term mole?

Mole SI unit used to measure the amount of a substance
equal to 6.02 x 1023 atoms, molecules, or particles Avogadro’s number Abbreviated by mol

Avogadro’s Number 6.02 X 1023 Used to count extremely small particles
Named in honor of Italian physicist Amedeo Avogardo Determined the volume of one mole of a gas

Conversions

Mole  Molecules, Atoms, or Particles
In order to convert moles to molecules atoms, or particles, you have to MULTIPLY the number of moles by Avogadro’s number (6.02 x 1023) Example: How many atoms are there in 4.0 moles?

How many atoms are there in 4.0 moles?
Moles  Atoms…MULTIPLY BY AVOGADRO’S NUMBER 2.4 x 1024 atoms

Molecules, Atoms, or Particles  Moles
In order to convert molecules, atoms, or particles to moles, you have to DIVIDE the number of moles by Avogadro’s number (6.02 x 1023) Example: How many moles are there in 7.14 x 1023 molecules?

How many moles are there in 7.14 x 1023 molecules?
Molecules  Moles…DIVIDE BY AVOGADRO’S NUMBER 1.19 moles

Practice

How many molecules are there in 3.5 moles?
Moles  Molecules…MULTIPLY BY AVOGADRO’S NUMBER 2.11 x 1024 molecules

How many particles are there in 9.6 moles?
Moles  Particles…MULTIPLY BY AVOGADRO’S NUMBER 5.78 x 1024 particles

How many moles are there in 5.75 x 1024 atoms?
Atoms  Moles…DIVIDE BY AVOGADRO’S NUMBER 9.55 moles

How many moles are there in 3.58 x 1023 particles?
Molecules  Moles…DIVIDE BY AVOGADRO’S NUMBER 0.59 moles

End Day 1

Molar Mass

Molar Mass the mass in grams of one mole of any pure substance
In other words, the molar mass of any element is equivalent to the atomic mass of that element in units of grams per mole; g/mol

Calculating Molar Mass
- To calculate the molar mass of a substance, you add the atomic mass of every element in the compound The total atomic mass is the molar mass of the substance.

What is the molar mass of N?
Example What is the molar mass of N? Step 1: determine the atomic mass N: 14 Step 2: add units g/mol molar mass = 14 g/mol

What is the molar mass of CO2?
Example What is the molar mass of CO2? Step 1: determine the mass of each element C: 12 O: 16 X 2 Step 2: add the masses to get the total atomic mass =44 Step 3: add units g/mol Molar mass = 44 g/mol

Practice What is the molar mass of NaCl?
58.5 g/mol What is the molar mass of H3O? 19 g/mol What is the molar mass of H2SO4? 98 g/mol

END

Mole  Gram Conversions

Review Mole SI unit used to measure the amount of a substance Abbreviate by mol Molar mass total atomic mass of every element in the compound Units: g/mol

What is the molar mass of NH3?
Step 1: determine the mass of each element N: 14 H:1 X 3 Step 2: total the masses 14+3=17 Step 3: attach the units 17g/mol

Mole  Gram Conversions
When given the number of moles, MULTIPLY by the molar mass of the substance. What is the mass of 5 moles of H2O?

What is the mass of 5.O moles of H2O?
Step 1: Write the given Step 2: Multiply by molar mass Step 3: Cancel the units Step 4: Solve 90 grams H2O

Gram  Mole Conversions
When given the number of moles, DIVIDE by the molar mass of the substance. How many moles are equivalent to 50g N?

How many moles are equivalent to 50g N?
Step 1: Write the given Step 2: Divide by the molar mass Step 3: Cancel the units Step 4: Solve 3.57 moles N

Practice

What is the mass of … 2.22 mol Ti 1.22 X 1023 mol Ag 4.5 mol H2SO4
106 g Ti 1.22 X 1023 mol Ag 1.32 X 1025 g Ag 4.5 mol H2SO4 441 g H2SO4

How many moles are consumed in…
5.62 g Kr mol Kr 55 g As 0.73 mol As 7.5 g NaCl 0.128 mol NaCl

End Day 2

Particles  Gram Conversions
Remember, particles, atoms, and molecules are all the same To convert particles to grams… 1st: convert particles to moles 2nd: convert moles to grams

Review When converting from moles to atoms, molecules, or particles, you must MULTIPLY by Avogadro’s number. When converting atoms, particles, or molecules to moles, you must DIVIDE by Avogadro’s number.

What is the mass of 2.5 X 1023 atoms of H2O?
Step 1: convert atoms to moles Step 2: convert moles to grams

Grams  Particles Conversions
Once again, remember particles, atoms, and molecules are all the same To convert grams to particles… 1st: grams to moles 2nd: convert moles to particles

How many molecules are in 4.5 g C?
Step 1: Convert grams to moles Step 2: Convert moles to molecules

Practice How many grams are in 5.0 X 1024 atoms of K?
What is the mass of 8.5 X 1023 molecules of NH2? How many particles are in 3.75 g Ca? How many molecules are in 96 g HBr2?

Practice On your own, work pg. 347: