Drill – Empirical/Molecular Formulas Drill
• Please complete #1 and #2
Agenda
•
•
•
•
Pass fwd empirical/molecular form WS
Limiting Reactants WS
Reminder: Mole Project due Mar 18
Stoichiometry Test - Friday
Limiting Reactants
Example
Your job is to attach arms on dolls in a doll
factory. If you have 600 arms and 350
dolls, how many finished dolls can you
make?
What is limiting your
production – the arms or the
dolls?
What do you have
in excess?
• Reagent = reactant
• Limiting Reactant – the reactant that
is completely consumed. This
reactant limits the amount of product
that is formed.
• Excess Reactant – the reactant that
is not limiting the reaction. There will
be leftovers of this reactant.
How to solve for limiting reactant
1. Write the balanced chemical
equation
2. Determine the moles of each
reactant
3. Determine how many moles of
product each reactant would make
using a mole ratio
4. The reactant that yields less product
is the limiting reactant.
• Start here pd 3
Copper reacts with sulfur to form copper (I)
sulfide. What is the limiting reagent when
80.0g Cu reacts with 25.0g S?
1. Write the balanced chemical equation
2Cu + S  Cu2S
Copper reacts with sulfur to form copper (I)
sulfide. What is the limiting reactant when
80.0g Cu reacts with 25.0g S?
2. Determine the moles of each
reactant.
80.0 g Cu
1
mole
Cu
x
=
63.55 g Cu
25.0 g S
x
1 mole S
32.06 g S
1.26 mol Cu
= .780 mol S
Copper reacts with sulfur to form copper (I)
sulfide. What is the limiting reactant when
80.0g Cu reacts with 25.0g S?
3. Determine how many moles of
product each reactant would make
using a mole ratio
1.26 mol Cu
1
mol
Cu
S
2
x
= .630 mol Cu2S
2 mol Cu
.780 mol S
1
mol
Cu
S
2
x
=
.780
mol
Cu
S
2
1 mol S
Copper reacts with sulfur to form copper (I)
sulfide. What is the limiting reactant when
80.0g Cu reacts with 25.0g S?
4. The reactant that yields less product
is the limiting reagent.
Copper yields .630 mol Cu2S
Sulfur yields .780 mol Cu2S
So Copper is the limiting reagent
Amount of Excess?
• In order to determine how much (mass)
of excess reactants there are, you must
figure out what mass of the excess
reactant got used up…then subtract
that from the initial mass.
Amount of Excess?
• Step 1 – Start with moles of product
formed (from limiting reactant).
• Step 2 – Convert back to moles of excess
reactant.
• Step 3 – Convert from moles to mass of
excess reactant.
• Step 4 – Subtract this value from the
original mass of excess reactant (given in
problem)
• Start here – pd 4B
Sample Problem
3 Fe + 4 H2O
Fe3O4 + 4H2
– When 36.0 g of water is mixed with 67.0 g of
Fe, which is the limiting reactant?
– Determine the grams of iron oxide produced.
– Determine the mass of excess reactant
remaining.
1. Convert both masses to moles and calculate the
number of moles of Fe3O4
67.0 g Fe = 0.400 mol Fe3O4
36.0 g H20 = 0.499 mol Fe3O4
2. Convert back to mass of excess reactant
0.400 mol Fe3O4 x 4 mol H20 x 18.02 g H20 =
1 mol Fe3O4 1 mol H20
28.8 g H20
3. Subtract this value from the original mass of
excess reagent (given in problem)
36.0 g H2O – 28.8 g H2O consumed =
7.2 g H2O remaining
Homework
• Mole Project
• Limiting Reactant Worksheet
Pd 4a – start here
Agenda
• Stoichiometry Test
• Hydrates with Worksheet
• Stochiometry Lab Data
Hydrates
• When salts combine chemically with water
and form unstable hydrated crystals
• Although in a chemical bond, this water of
hydration maintains its characteristic
composition
• Instead of H20Na2SO14, we write
Na2SO4 H2O
Homework
• Hydrates WS
• Stoichiometry Test
Drill – pd 3
• Determine the percentage of water in the
following hydrate:
Sc(NO3)3 · 10H2O [scandium(III)
nitrate decahydrate]
Answer
• 43.8% water
Drill – all classes
In an experiment, 3.25 g of NH3 are allowed to react
with 3.50 g of O2.
NH3 + O2
NO + H2O
a. Which reactant is the limiting reagent?
b. How many grams of NO are formed?
c. How much of the excess reactant remains after
the reaction?
Drill – all classes
In an experiment, 3.25 g of NH3 are allowed to react
with 3.50 g of O2.
NH3 + O2
NO + H2O
a. Which reactant is the limiting reagent? O2
b. How many grams of NO are formed? 2.63 g NO
c. How much of the excess reactant remains after
the reaction? 1.71 g NH3 left
Make sure to turn in :
• Composition of Hydrates WS
• Limiting Reactants WS
• Lab Calculations
Next class
• Wear close-toed shoes – Lab
• Wed or Th will be your test
• Does anyone need a mole pattern?
Agenda
• Lab Calculations
• Mixed Stoichiometry/Limiting Reactants
WS
• Review Sheet if finished
Drill
• Read the Introduction of Lab
• Change Lab to read Percent Composition
of Epsom Salt
Lab
• Only heat crucible once for 10 minutes
• Allow it to cool for 10 minutes
• Make sure crucible is cool before handling
it.
Lab Groups – pd 4B
1. Stephanie, Chris H.
2. Ben, Comfort
3. Jessica, Zach
4. John, Chris J
5. Sahra, O
6. Amelia, Valentina
7. Emileigh, Caine
8. Troy, Claire,Max
9. Shivani, Anjali
10.Josh, Becky
11.Sophia, Max
12.Joey, Alexis
Homework
• Review WS