Conversion Practice
Name ___________________________________
Show all work, round to the nearest hundredth, show proper units Date __________________________ Per ______
HOW TO FIND MOLAR MASS
Atomic mass from the periodic table.
Ex 1: CO2
Steps for finding molar mass:
1. Separate each element from the formula
2. Identify the number of moles per element
3. Multiply the number of moles of each element by their atomic
mass from the periodic table
4. Add the numbers and include the unit: g/mol
1_ mol C x 12.01__ g = 12.01 g/mol
2_mol O x 16.00___g =
32.00 g/mol
Answer =
44.01 g/mol
This is the number of
moles for this element
This is your final answer, the molar mass.
Your turn: Calculate the molar mass for the following compounds. Show all work and include proper units. You will use
these answers for the conversion problems below.
1. Ca3N2
2. Al(OH)3
3. Fe2O3
4. H2O
HOW TO FIND MOLES WHEN GIVEN MASS (GRAMS)
given grams
This is your given grams
1 mole
= answer moles (mol)
grams
(This is molar mass)
Ex 2: Calculate the number of moles in 2.5g of CO2.
2.5g of CO2
1 mol CO2
=0.0600000
mol
44.01 g CO2 g
This is the molar mass that was
calculated in example 1
5.) Your turn: Calculate the number of moles in 235.00g of Ca3N2
=
You get this answer by dividing the
top number by the bottom number, so
2.5 divided by 44.01
HOW TO FIND MASS (GRAMS) WHEN GIVEN MOLES:
This is your given
moles
given moles grams (again, this is molar mass) = answer grams (g)
1mole
Ex 3: How many grams are in 7.25 moles of CO2 ?
7.25 moles of CO2
44.01 g CO2
This is the molar mass of CO2 which
was calculated in example 1
=
319.07 g
You get this answer by multiplying
the two numbers that are side by side
So 7.25 x 44.01
1 mol CO2
6.) Your turn: How many grams are in 3.12 x 103 moles of Al(OH)3?
=
HOW TO FIND REPRESENTATIVE PARTICLES (ATOMS, MOLECULES, FORMULA UNITS , IONS)
WHEN GIVEN MOLES:
Use Avogadro’s number here
6.02 x 1023 particles
Given moles
1 mole
=
Answer in molecules, atoms, or
formula units. Depends on what
word is used in the question
Ex 4: How many molecules of CO2 are in 14 moles of CO2?
14 moles CO2
6.02 x 1023 molecules CO2
=
1 mol CO2
8.43 x 1024 molecules CO2
To get the answer, you would have to
multiply 14 by 6.02 x 1023
7.) Your turn: How many molecules of H2O are in 6.98 x 104 moles of H2O?
=
HOW TO FIND MOLES WHEN GIVEN REPRESENTATIVE PARTICLES (ATOMS, MOLECULES,
IONS, FORMULA UNITS)
Given particles
1 mole
= answer in moles (mol)
6.02 x 1023 particles
Ex 5: How many moles of C (Carbon) are in 3.4 x 1023 atoms of C (Carbon) ?
3.4 x 1023 atoms C
1 mole C
6.02 x 1023 atoms C
= 0.56 mol C
To get the answer, you would have to divide
3.4 x 1023 atoms CO2 by 6.02 x 1023
8.) Your turn: How many moles are in 1.33 x 1039 formula units of Fe2O3?
HOW TO FIND REPRESENTATIVE PARTICLES (ATOMS, MOLECULES, IONS, FORMULA UNITS)
WHEN GIVEN MASS (GRAMS):.
Given grams
6.02 x 1023 particles =
1 mole
(molar mass) grams
1 mole
Answer in molecules, atoms, or
formula units. Depends on what
word is used in the question
Ex 6: How many molecules of CO2 are in 355 g of CO2?
355 g CO2
6.02 x 1023 molecules CO2
1 mole CO2
44.01 g CO2
1 mole CO2
= 4.86 x 1024 atoms CO2
To get the answer, multiply 355 by 6.02 x 1023
and divide that answer by 44.01
9.) Your turn: How many formula units are in 244.86 g Al(OH)3?
=
HOW TO FIND MASS (GRAMS) WHEN GIVEN REPRESENTATIVE PARTICLES (ATOMS, MOLECULES,
ION, FORMULA UNITS):
given particles
1 mole
23
(molar mass) grams
6.02 x 10 particles
= Answer in grams
1 mole
Ex 7: How many grams are in 9.20 x 1027 molecules of CO2?
9.20 x 1027 molecules of CO2
1mole CO2
44.01 g CO2
6.02 x 1023 molecules CO2
1 mole CO2
=
6.73 x 105 g CO2
10.) Your turn: How many grams are in 3.38 x 1022 formula units of Fe2O3?
=