10 January 2011
Take Out Homework: Week 17 p. 3
Objective: SWBAT define and identify the
limiting reagent in a chemical reaction.
Do Now: Which type of reaction?
a. AX + BY  BX + AY
b. 2HgO(s)  2Hg(l) + O2(g)
Agenda
Do now, homework check
II. Review types of reactions
III. Limiting reagent demonstration/mini lab
Homework: Week 18 Homework pages 1-2: Tues
Limiting Reagent Lab: Due Weds.
Quiz on Types of Reactions tomorrow
(includes one mass to mass conversion problem!)
(10 min)
I.
Limiting Reagents
Demonstration
Solid sodium bicarbonate reacts with a
solution of acetic acid to produce…
 You will be working with your lab group to carry
out one trial of this experiment.
 Listen carefully to the verbal directions!
 When you finish your trial, bring your flask +
balloon to the front (don’t take the balloon off the
flask!)
 Then, finish page 1 and page 2 of the lab handout
Group Amt of
baking
soda
1a
2g
1b
2g
2a
4g
2b
4g
3a
6g
3b
6g
Amt of
vinegar
Circumference Any baking soda
of balloon (cm) left over?
50ml
(2.5g)
50ml
(2.5g)
50ml
(2.5g)
50ml
(2.5g)
50ml
(2.5g)
50ml
(2.5g)
28.5cm
Nah
31.0
NO
36.0cm
no
36.1cm
no
36.0cm
YES
36.0
YESSSSSSSSSSSSSS
SSSSSS
For the rest of the period…
Complete the lab packet with your group.
 Ask me questions if you have them!


If you finish early (wow!) begin the
homework (Week 18 pages 1-2)
Homework
Week 18 Homework pages 1-2: tomorrow
Limiting Reagent Lab: Due Weds.
Quiz on Types of Reactions tomorrow
(includes one mass to mass conversion
problem!) (10 min)
Extra Help TOMORROW 3:30-4:30 pm
NaHCO3(s) + CH3COOH(aq) 
CO2(g) + H2O(l) + NaCO3(aq)
14 January 2011
Take Out Homework:
Limiting Reagents Lab
 Objective: SWBAT determine the
limiting reagent in a chemical reaction
word problem.
 Do now: For our limiting reagents lab,
describe how we could have checked to see
if there was excess vinegar in flask 1.

Agenda
Do now
II. Homework check
III. Determining the limiting reagent
IV. Practice Problems
Homework:
Week 18 Homework p. 1-3: Tuesday
I.
For one sandwich:
1 roll
1 slice
2 slices
1 leaf
2 slices
You have
2 rolls
5 slices
6 slices
4 leaves
8 slices
What is the limiting ingredient?
Which ingredients are in excess?
Vocab
Limiting reagent: the reactant that limits
or determines the maximum amount of
product that can be formed in a reaction.
Excess reagent: reactant that is not
completely reacted; extra
Ex. 1
2Na(s) + Cl2(g)  2NaCl(s)
If 6.70 moles of sodium is reacted with
3.20 moles of chlorine gas…
a. What is the limiting reagent?
b. How many moles of NaCl are
produced?
Ex. 1
C2H4(g) + 3O2(g)  2CO2(g) + 2H2O(g)
If 2.70 moles of C2H4 (ethylene) is reacted
with 6.30 moles of oxygen gas…
a. What is the limiting reagent?
b. How many moles of water are
produced?
Complete the front page of the handout.
Practice Problems
Front: Moles problems
 Back: Mass problems


Bonus! If you finish early, complete part c
on the front and back. Due Tues.
Practice Problems! (Part 1)
C2H4(g) + 3O2(g)  2CO2(g) + 2H2O(g)
1. If 15.0 moles of ethene is reacted with 10.0
moles of oxygen…
2. If 0.50 moles of ethene are reacted with 0.25
moles of oxygen…
a. What is the limiting reagent?
b. How much water is produced?
**c. How much of the excess reagent is left?**
Homework


Week 18 Homework p. 1-3: Tues.
Missing Work? Still can’t write and
balance an equation? Think mass
conversions are impossible?
 Extra Help Tuesday 3:30-4:30
A: 18 Jan. 2011
Take Out Homework: Week 18 p. 3
 Objective: SWBAT determine the limiting
reagent in grams in a chemical reaction
word problem.
 Do now: 2H2(g) + O2(g)  2H2O(l)
a. If 10 moles of H2 are reacted with 4 moles
of O2, which is the limiting reagent?
b. How many moles of water can be made?

Agenda
Do now, Homework check
II. LR examples with grams
III. Practice Problems
Homework: Week 18 Homework p. 4: Weds.
Finish Limiting Reagents worksheet: Weds.
I.
Ex. 1
2Na(s) + Cl2(g)  2NaCl(s)
If 2.0 grams of sodium is reacted with 3.0
grams of chlorine…
a. What is the limiting reagent?
b. How many grams of NaCl are
produced?
Ex. 2
C2H4(g) + 3O2(g)  2CO2(g) + 2H2O(g)
If 5.00 grams of ethylene is reacted with
1.00 gram of oxygen gas…
a. What is the limiting reagent?
b. How many grams of water are
produced?
**c. How many grams of the excess
product are left?**
Complete page 2 of the handout
Practice Problems
Back: Mass problems
 Due at the end of the class!


Bonus! If you finish early, complete part c
on the front and back. Bonus due
tomorrow.
Homework


Week 18 Homework p. 4: tomorrow
Finish Limiting Reagents worksheet
bonus: tomorrow
A: 19 January 2011
Take Out Homework: Week 18 p. 4
and Limiting Reagents Worksheet
 Objective: SWBAT calculate percent yield
of a product of a reaction.
 Do now: 2H2(g) + O2(g)  2H2O(l)
a. If 6 moles of H2 are reacted with 4 moles of
O2, which is the limiting reagent?
b. How many moles of water can be made?

Agenda
Do now
II. Homework check
III. % yield notes and examples
IV. Practice problems
V. Bubblegum lab!
Homework: Week 18 Homework p. 5-6,
Finish bubblegum lab: Thurs.
I.
Percent Yield
C2H4(g) + 3O2(g)  2CO2(g) + 2H2O(g)
If you calculate that the reaction of 5.00
grams of ethylene with 3.00 grams of
oxygen will yield 2.75 grams of carbon
dioxide, should you expect the actual
reaction to really yield exactly that much?
Why or why not?
Theoretical yield: maximum amount of
product that could be formed given the
amounts of reactants.
(Calculated on paper.)
Experimental yield: the amount of
product that actually forms during an
experiment
(Determined by doing an experiment.)
Percent Yield is usually < 100%
Why?
• Reaction not going to completion
• Impure reactants
• Side Reactions: a product reacts with a
reactant
• Loss during filtration or pouring between
containers
Ex. 1
CaCO3(s) → CaO(s) + CO2(g)

You calculate that, with the masses of
reactants used, your experiment should
have yielded 3.00 grams of solid calcium
oxide. However, you only got 2.00 grams
of calcium oxide. Calculate the percent
yield.
Ex. 2
CaCO3(s) → CaO(s) + CO2(g)
a. What is the theoretical yield of CaO if
24.8 grams of CaCO3 is heated?
b. What is the percent yield if 13.1 g CaO is
actually produced?
Ex. 3
Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)
When 84.8 g of iron (III) oxide reacts with
an excess of carbon monoxide, 54.3 g of
iron is produced. What is the percent
yield?
Practice Problems!
Fe2O3(s) + 3CO(g)  2Fe(s) + 3CO2(g)
1.
2.
3.
You calculate that your reaction should have
produced 10.0 g of iron, but only 6.8 grams
were produced. What is the percent yield?
When 10.0 g of iron (III) oxide reacts with an
excess of carbon monoxide in an experiment,
only 6.45 g of iron is actually produced. What
is the percent yield?
When 5.00 g of iron (III) oxide is reacted with
1.00 g carbon monoxide, 1.20 grams of iron is
produced. What is the percent yield? (Hint:
Calculate the limiting reagent FIRST!)
Bubblegum Lab!
What percent of Dubble Bubble is sugar,
by mass?
 Compared to the Nutrition Facts, what is
your percent yield of sugar from Dubble
Bubble?


Work with your partner. Choose one
“chewer” and one “balancer.”
Homework
Week 18 Homework p. 5-6: Thurs.
Finish bubblegum lab: Thurs.
Alka Seltzer
Contains:
Aspirin
Citric acid
NaHCO3 (sodium bicarbonate)
How much of Alka Seltzer is actually
sodium bicarbonate (NaHCO3)?
P. 3 #1
NaHCO3(s) + CH3COOH(aq)  CH3COONa(aq) + CO2(g) +
H2O(l)
Solid sodium bicarbonate (in the Alka
Seltzer) reacts with a solution of acetic
acid (in the vinegar) to produce a solution
of sodium acetate, carbon dioxide gas, and
liquid water.
Using stoichiometry, if we find the mass of
the carbon dioxide released, we can
calculate the mass of the sodium
bicarbonate in the alka seltzer!
And then, the percent by mass of sodium
bicarbonate in the alka seltzer!
Determining a Limiting Reagent
Lab
Safety:

No eating or drinking

Used chemicals can be washed down the
sink with water.

Do not use lab materials to design your own
lab.
Procedure
You will be reacting different amounts of
acetic acid and water with an alka seltzer
tablet.
Read directions carefully.
Refer to data table 1 on page 2
Record qualitative observations.
Record data on the back page.
Graphing Experimental Data
Goal: To determine the limiting reagent in
the reaction
NaHCO3(s) + CH3COOH(aq)  CH3COONa(aq) +
CO2(g) + H2O(l)
Graph amount of NaHCO3 vs. amount of
CH3COOH
Parts of a Graph
CH3COOH (g)
Title
9
8
7
6
Scale
Units
5
Plot Points
4
(do not connect!)
3
2
1
NaHCO3 (g)
1
2
3
Scale
Units
4
5
6
7
8
9
Analysis
What is the trend of the data?
Increasing? Decreasing? Constant? Steep
slope? Flat slope? Shape (linear, quadratic?)
As (x-value) ______, (y-value) ______.
Write one very complete paragraph describing
the trends in your data.
Conclusions
What can you conclude about this
experiment based on your graph?
Why do you see the trend in your data?
What is the LR? When? How do you know?
What is in excess? When? How do you
know?