Document Sample

```					   Limiting Reagents

understand stoichiometry
problems with a limiting reagent.
Simulation
Sam works at the Salem Sandwich Shoppe.
Sam expected a big day on Tuesday, so
he ordered the following:
5 pounds of bologna (10 slices per pound)
4 pounds of cheese (16 slices per pound)
5 packages of buns (12 buns per package)

How many sandwiches can Sam make?
How Many?
• First, let’s look at how Sam will assemble
each sandwich:
1 slice bologna + 1 slice cheese on 1 bun

• Now we need to determine how many
slices of bologna, how many slices of
cheese and how many buns did Sam buy.
Use factor label.
Limiting Reagent
• Which of the ingredients will run out first?

• Sam has:
– 50 slices of bologna
– 64 slices of cheese
– 60 buns
CORRECT
• You got it right, the bologna is going to run
out first because there are only 50 slices.

• Therefore we can deduce that Sam can
only make 50 sandwiches.

• Sam will have excess cheese and buns.
Simulation Conclusion
• Even though Sam started with 5 pounds of
bologna and only 4 pounds of cheese; he
ran out of bologna first.
• Why? It matter how many slices, not the
mass of the material when determining
which ingredient runs out first.
• Now let’s relate this concept to chemistry
and stoichiometry.
Problem #1
• How many grams of product can you
produce if you react 26.28g of strontium
with 39.95g of bromine.

• Write a balanced equation.

• Convert both masses to moles.
Sr + Br2  SrBr2
26.28g Sr     1 mole Sr     0.30 moles Sr
87.6g Sr

39.95g Br2     1 mole Br2   0.25 moles Br2
159.8g Br2

Which reactant is the limiting reagent?
Br2 is the limiting reagent!
The Br2 will run out first because there are
less moles of Br2 than Sr.

Now calculate the mass of product using the
number of moles of the limiting reagent.
STOICHIOMETRY BABY
0.25moles Br2     1 mole SrBr2   0.25moles SrBr2
1 mole Br2

0.25moles SrBr2     247.4g SrBr2     61.85g SrBr2
1 mole SrBr2
Problem #2
How many grams of sodium chloride will be
produced if 0.93g of sodium oxide reacts
with 1.67g of barium chloride?

Write a balanced equation.
Convert both grams to moles.
Determine the limiting reagent.
Use the limiting reagent calculate the mass of NaCl.