Stoichiometry
2: grams to
grams
Chemistry 2012-2013 Ms. Boon
10.18 & 10.19
Catalyst
Objectives:
I can perform
gram to gram
conversions.
Agenda:
Catalyst
Stoichiometry Puzzle
Notes: gram to gram
Practice Problems
Exit Slip
These questions are a mini-review… We need
to use these skills today in class.
1.
What is the molar mass of water? (Hint:
use the periodic table.)
2.
What is the mass (grams) of 3 moles of
water?
3.
How many moles is 180 g water?
Helpful materials for today
Objectives:
I can perform
gram to gram
conversions.
Agenda:
Catalyst
Stoichiometry Puzzle
Notes: gram to gram
Practice Problems
Exit Slip
Mass (grams) of
COMPOUND A
Divide by
molar mass
(g/mol) of
compound A
Mass (grams) of
COMPOUND B
Multiply by mole
ratio from
balanced equation
Amount (Moles) of
COMPOUND A
Divide by
Avogadro’s #
(6.02 x 1023)
# particles (atoms
or molecules) of
COMPOUND A
Multiply by
molar mass
(g/mol) of
compound B
Amount (Moles) of
COMPOUND B
Mol Compound B
Mol Compound A
Multiply by
Avogadro’s #
(6.02 x 1023)
# particles (atoms
or molecules) of
COMPOUND A
What are we converting?
Look for clues in the question!
Na2O + H2O 
2NaOH
1.
How many moles of Na2O are needed to produce 22
moles of NaOH?
A: moles of NaOH to moles of Na2O
2.
How many grams of Na2O are needed to produce 30
moles of NaOH?
A: moles of NaOH to grams of Na2O
3.
How many moles of Na2O are needed to produce 200g of
NaOH?
A: grams of NaOH to moles of Na2O
4.
How many grams of Na2O are needed to produce 58 g of
NaOH?
A: grams of NaOH to grams of Na2O
Quick Check

What type of conversion is this question?

How many grams of oxygen gas (O2) can be
made from the decomposition of 136g of
hydrogen peroxide (H2O2)?


2 H2O2  2 H2O + O2
Vote for your answer choice!
1.
2.
3.
4.
Grams of O2 to grams of H2O2?
Moles of O2 to grams of H2O2?
Grams of H2O2 to grams of O2?
Grams of H2O2 to moles of O2?
Activity: Stoichiometry Puzzle

You and your partner will receive a 12 puzzle pieces
with stoichiometry problems on them.

Your task is to sort the problems into four piles
according to the type of conversion in the problem.

The four types of conversions are:





Gram to gram
Mole to mole
Gram to mole
Mole to gram
When you think you have sorted the problems correctly,
raise your hand to get your answers checked.
Mole to Mole Conversions are part
of every stoichiometry problem.
Multiply by mole
ratio from
balanced equation
Amount (Moles) of
COMPOUND A
Amount (Moles) of
COMPOUND B
Mol Compound B
Mol Compound A
We worked on this part earlier this week.
Mass (grams) of
COMPOUND A
Divide by
molar mass
(g/mol) of
compound A
Mass (grams) of
COMPOUND B
Multiply by mole
ratio from
balanced equation
Amount (Moles) of
COMPOUND A
Multiply by
molar mass
(g/mol) of
compound B
Amount (Moles) of
COMPOUND B
Mol Compound B
Mol Compound A
• Today we are adding gram to gram
conversions.
• We already know how to do all the steps.
Today we are putting them together.
Example 1: How many grams of oxygen gas (O2) can be
made from the decomposition of 136g of hydrogen
peroxide (H2O2)?
2 H2O2  2 H2O + O2
O2 of
Mass64g
(grams)
COMPOUND B
Mass
136g
(grams)
H2O2 of
COMPOUND A
Divide
Dividebyby
molar mass
34
g/mol
(g/mol)
of
compound A
Multiply by mole
ratio from
balanced equation
Amount
4 mol(Moles)
H2O2 of
COMPOUND A
Multiply by
Multiply
by
molar mass
32
g/mol
(g/mol)
of
compound B
Amount
(Moles)
2 mol
O2 of
COMPOUND B
Mol
Compound
B
1 mol
O2
Mol
Compound
2 mol
H 2 O2 A
Example 2: How many grams of hydrogen peroxide (H2O2)
are needed to produce 180g water (H2O)?
2 H2O2  2 H2O + O2
340g
H2O2 of
Mass
(grams)
COMPOUND B
Mass
180g
(grams)
H2O of
COMPOUND A
Divide
Dividebyby
molar mass
18
g/mol
(g/mol)
of
compound A
Multiply by mole
ratio from
balanced equation
Amount
(Moles)
10 mol
H2O of
COMPOUND A
Multiply by
Multiply
by
molar mass
34
g/mol
(g/mol)
of
compound B
Amount
(Moles)
10 mol
H2O2 of
COMPOUND B
Mol
Compound
2 mol
H2O2 B
Mol
Compound
A
2 mol
H 2O
Mole to Mole Conversion
Multiply by mole
ratio from
balanced equation
Amount (Moles) of
COMPOUND A
Amount (Moles) of
COMPOUND B
Mol Compound B
Mol Compound A
Example: How many moles aluminum are needed if 3 mol Fe2O3 completely
react.
Fe2O3 + 2 Al→ 2 Fe + Al2O3
Converting from mol Fe2O3 to mol Al
3 mol Fe2O3
2 mol Al____ = 6 mol Al
X 1 mol Fe O
2 3
Gram to Gram Conversions
Mass (grams) of
COMPOUND A
Divide by
molar mass
(g/mol) of
compound A
Mass (grams) of
COMPOUND B
Multiply by mole
ratio from
balanced equation
Amount (Moles) of
COMPOUND A
Multiply by
molar mass
(g/mol) of
compound B
Amount (Moles) of
COMPOUND B
Mol Compound B
Mol Compound A
Example: How many grams of BrCl form when 140g Cl2 react with excess Br2?
Br2 + Cl2 → 2BrCl
140g Cl2 ÷ 70 g/mol = 2 mol Cl2 X 2 mol BrCl = 4 mol BrCl X115 g/mol = 460 g BrCl
1 mol Cl2
Gram to Mole Conversion
Mass (grams) of
COMPOUND A
Divide by
molar mass
(g/mol) of
compound A
Multiply by mole
ratio from
balanced equation
Amount (Moles) of
COMPOUND A
Amount (Moles) of
COMPOUND B
Mol Compound B
Mol Compound A
Example: How many moles of BrCl form when 210g Cl2 react with excess Br2?
Br2 + Cl2 → 2BrCl
210g Cl2 ÷ 70 g/mol
= 3 mol Cl2 X 2 mol BrCl =
1 mol Cl2
6 mol BrCl
Mole to Gram Conversion
Mass (grams) of
COMPOUND B
Multiply by mole
ratio from
balanced equation
Amount (Moles) of
COMPOUND A
Multiply by
molar mass
(g/mol) of
compound B
Amount (Moles) of
COMPOUND B
Mol Compound B
Mol Compound A
Example: How many grams of BrCl form when 5 mol Cl2 react with excess Br2?
Br2 + Cl2 → 2BrCl
5 mol Cl2 X 2 mol BrCl = 10 mol BrCl X115 g/mol = 1150 g BrCl
1 mol Cl2
Exit Slip (3e) 10.18 & 19
N2 + 3 H2 2 NH3
1.
What is the mole ratio of H2 to NH3?
2.
How many moles of H2 are needed to produce 10 moles
NH3?
3.
How many moles H2 are needed to produce 170 grams
NH3? (molar mass of NH3 is 17g/mol)
4.
How many grams H2 are needed to produce 170 grams
NH3? (NH3 =17g/mol; H2 = 2g/mol)
Challenge: If you have 1 mol N2 and 6 mol H2 , how many moles of
NH3 are produced? Why?
Tonight’s HW: Read pp. 306-307, practice problems #1-4 on p.
307; problems p. 334 #1 & 3