Honors Chemistry
Unit 11
 Stoichiometry
 Molar mass
 % Composition
 Empirical and Molecular Formulas
 Molecules, Moles, Grams conversions
 Limiting Reagent
 % Yield
 Lab Report
1
At the conclusion of this unit, the student will be able to:
1.
Demonstrate an understanding of stoichiometry conversions (moles to moles, mass to mass, atoms/molecules to atoms/molecules).
2.
Identify the limiting reactant and use the limiting reactant to predict the amount of product produced.
3.
Demonstrate an understanding of %mass (%composition).
4.
Demonstrate an understanding of empirical/molecular formulas.
We are looking for:
1a. Calculate the molar mass of a compound/element using a periodic table.
1b. Using molar mass and unit analysis, convert moles of a given compound to grams of that compound and vice versa.
1c. Using the molar ratio from a balanced chemical reaction and unit analysis, convert moles of one
compound to moles of another compound from the same reaction.
1d. Using Avogadro’s number and unit analysis, convert atoms/molecules of a compound to moles
of that compound.
1e. Using molar mass and mole ratio convert from grams of one compound to grams of another
compound in one long unit analysis calculation (or atoms/molecule instead of grams).
2a. Using stoichiometry conversions, determine which reactant will run out first.
-Convert the amount of reactant “A” you have to the amount of reactant “B”; this is the amount
of reactant “B” you will need.
-Compare the amount of reactant “B” needed to the amount of reactant “B” you have.
-If the amount of reactant “B” needed is more than the amount you have, then reactant “B” is
the limiting reactant.
2b. Use the limiting reactant to calculate the amount of product produced.
3a. Calculate the %mass (%composition) for each element in a compound.
4a. Use %composition to calculate the empirical formula for a compound given the elements present.
4b. Use the molar mass of the compound and the empirical formula to determine the molecular formula.
2
Stoichiometry
From 2 greek words:
Stoicheion = element
1792 – German Chemist
Metron = measure
Jeremias Benjamin Richter
Is concerned with the amount of substances involved in a reaction
Composition stoichiometry = mass relationships between elements in compounds
Ex: Na2SO4
2 Na / 1 SO4
Reaction stoichiometry = mass relationships between reactants and products (chemical reactions).
**Must always have a balanced chemical equation.
The coefficients represent the number of moles of the reactants and products.
2H2 + 1O2  2H2O
Molar Ratio = factor that relates two substances in a chemical equation.
The ratio of hydrogen to oxygen =
2 mole H2
1 mole O2
The ratio of water to hydrogen = 1 mole H2O
2 mole H2
The numbers cannot represent mass ratios (not 2 g H2 to 1 g O2)
Avogadro’s Number = Number of particles(atoms, molecules, or formula units) in a mole
6.02 X 1023
=
602,000,000,000,000,000,000,000
(Named after Amadeo Avogadro – 1776-1856 Italian chemist and physicist)
Molar Mass
Mass in grams of one mole of an element or compound.
Numerically equal to the atomic weight of the element given on the periodic table
or
The sum of all the atomic weights of all the atoms in the formula.
3
Molar Mass Examples
1. NaCl = 22.99 + 35.45 = 58.44 g/mole = g__
mole
2. CuSO4  5H2O = 63.55 + 32.07 + 4(16.00) + 5(18.00)
= 159.62 + 90
= 249.62 g/mole
**Report all Molar Masses to 2 Digits After the
Decimal!!**
Calculate the Molar Mass for each of these compounds.
1.
KCl
2.
Li2SO4
3.
(NH4)2C2O4  H2O
4.
Potassium Hydroxide
5.
Copper (II) Bromide
6.
Magnesium Phosphate
7.
Trisilicon Heptoxide
4
Using Molar Mass
Converting Moles to Grams
and
Converting Grams to Moles
Use the molar mass to convert the given moles into grams or given grams to moles. Write the answer
to the problem on the line provided. Show all of your work in the space on the right using factor label
method. Report all answers to appropriate sig. figs. using the given moles or mass in the
problem.
Work Space
__________ 1) 7.800 moles of Fe2O3
__________ 2) 100.2 moles of Pb(NO3)2
___________3) 1.22 moles of CO2 to grams
__________ 4) 120.8 grams of K2SO4 to moles
__________ 5) 4.6 grams of MgCl2 to moles
__________ 6) 2.3 grams of Ba3(PO4)2 to moles
5
Using Avogadro’s Number (6.02x1023 )
Converting Moles to Molecules (particles, atoms)
And Back Again
1) 4.50 Moles NaCl = ? Molecules of NaCl
2) 6.62 x 1024 Molecules of H2O = ? Moles of H2O
3) 91.20 Moles of CO2 = ? Molecules of CO2
4) 3.01 x 1023 Molecules CuCl2 = ? Moles of CuCl2
5) 1345.9 Moles MgO = ? Molecules of MgO
6) 4.87 x 1035 molecules of H2O contains how many atoms of hydrogen?
7) 2.36 moles of FeCl3 contains how many atoms of chlorine?
6
More Converting…
Using Avogadro’s Number and Molar Mass
1) Iron
18.06x 1023 atoms or iron = ? grams iron
2) CuSO4
1.20 x 1028 molecules CuSO4 = ? grams CuSO4
3) MgCl2
380.84 grams MgCl2 = ? molecules MgCl2
4) Pb(NO3)2
82.81 grams Pb(NO3)2 = ? molecules Pb(NO3)2
5) H2SO4
37.6 grams H2SO4 = ? atoms of oxygen
6) Al2(SO4)3
75.26 grams Al2(SO4)3 = ? atoms of sulfur
7
Moles And Compounds Worksheet
Directions: Write the answer to the problem on the blank provided. The correct set-up
must be to the right of the problem.
______________1) 0.738 moles of Fe2O3 to grams
______________2) 50.5 g of FeBr3 to moles
______________3) 1.51 x 10
23
molecules of Lead(II) iodide to moles
______________4) 0.445 moles of Carbon tetrachloride to molecules
______________5) 0.538 moles of Ce2(CO3)3 to grams
______________6) 150.4 g of Ce(CO3)2 to moles
______________7) 7.22 x 10
25
molecules of CuCl2 · 4 H2O to moles
______________8) 1.45 moles of Pb(C2H3O2)2 to grams
______________9) 1.22 x 10
24
molecules of CO2 to grams
_____________10) 19.3 grams of H2O to molecules
8
Lab: Determining the Number of Moles and Molecules Used Up in a Burning Candle
Purpose: to burn candle wax and to determine the number of moles and molecules of wax converted to
carbon dioxide and water.
Mass of plate____________g
Mass of candle and plate before burning:______________g
Mass of candle before burning:_____________________g
Light the candle and allow it to burn for 5 minutes. While it is burning, complete a-c below. Do NOT play
with the wax!
After 5 minutes, carefully blow out the candle.
Reweigh the candle
Mass of candle and plate after burning:________________g
Calculate the mass of candle wax burned:_______________g
Wax is a mixture of hydrocarbons. C25H52 can be used as a representative hydrocarbon in the mixture.
a) Write the equation for the burning (combustion) of wax below:
b) What 2 resources are used up as the candle burns?
c) What has happened to the atoms in these resources?
d) What is the molar mass of wax?_________________
e) How many molecules of wax were reacted during the burning?
f) How many moles of CO2 were produced?
g) How many gram of H2O were produced?
h) How many grams of O2 were reacted with the wax?
9
10
Percent Composition Problems
Percent composition is the percent by mass that each element contributes to the entire molar
mass of a compound.
Ex) H2O molar mass= 18.02g/mol
%H= (2.02/18.02) x 100 = 11.21%
%O= (16.00/18.02) x 100 = 88.79%
#1-3, find the percent composition of all of the elements in the following compounds:
1.
CuBr2
Cu ________
Br________
2. NaOH
Na________
O_________
H_________
3. (NH4)2S
N_________
H_________
S_________
4. % Barium in Ba(NO3)2
5. % Li in Li2O
11
6. % Phosphorus in Ca3(PO4)2
7. In 42.0 grams of MgO, how many grams of magnesium are there?
*you must first determine the %Mg in MgO and then apply that % to the given mass.
8. In 75.5 grams of H2O, how many grams of hydrogen are there?
9. How many grams of nitrogen are in 83.6 grams of Fe(NO3)3?
12
Empirical & Molecular Formulas
Emprical Formula:
Write the empirical formulas for each of the following:
1. P4O6 ____________________
2. C6H9 ___________
3. CH2OHCH2OH ____________
4. BrCl2 __________
5. C6H8O6 _________________
6. C10H22 __________
7. Cu2C2O4 _________________
8. Hg2F2 __________
#8-10, determine the empirical formula with the given information in each problem.
8. A compound composed of 10.0% carbon (C), 58.6% chlorine (Cl) and 31.4% fluorine (F).
9. A compound composed of: 72% iron (Fe) and 28% oxygen (O)
10. A compound composed of: 0.556g carbon (C) and 0.0933g hydrogen (H)
13
Empirical Formula Practice
1) Determine the empirical formula of methane given that 6.0 g of methane can be decomposed
into 4.5 g of carbon and 1.5 g of hydrogen.
2) Determine the empirical formula of the compound made when 8.65 g of iron combines with
3.72 g of oxygen.
:
3) The composition of a compound is 40% sulfur and 60% oxygen by weight. What is its empirical
formula?
4) Pure formaldehyde consists of 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen. What is its
empirical formula?
5) Determine the empirical formula of a compound that is 29.0% sodium, 40.5% sulfur, and 30.4 %
oxygen by weight.
14
Molecular Formula =
#1-5, determine the molecular formula with the given information in each problem.
1.
A compound with a molar mass of 70g/mole and an empirical formula of CH2
2. A compound with a molar mass of 46.0g/mole and an empirical formula of NO2.
3. A compound with an empirical formula of C2H4O and a molar mass of 88 grams/mole.
4. A compound with an empirical formula of CFBrO and a molar mass of 380.7 grams per mole.
5. A compound with an empirical formula of C2H8N and a molar mass of
46 grams / mole
15
Mixed Practice (% composition, empirical and molecular formulas)
1. Find the percentage composition for each element in Cu2S.
2. As some salts crystallize from a water solution, they bind water molecules in their crystal
structure. Sodium carbonate forms such a hydrate, in which 10 water molecules are
present for every formula unit of sodium carbonate. Find the mass percentage of water in
sodium carbonate decahydrate, Na2CO3•10H2O, which has a molar mass of 286.14 grams
per mole.
3. Magnesium hydroxide is 54.87% oxygen by mass. How many grams of oxygen are in 175
grams of magnesium hydroxide?
4. Analysis of a 10.150 grams of sample of a compound known to contain only phosphorus and
oxygen indicates a phosphorus content of 4.433 grams. What is the empirical formula of
this compound?
5. If 4.04 grams of Nitrogen combine with 11.46 grams Oxygen to produce a compound with a
formula mass of 108.0 g/mole. What is the molecular formula of this compound?
16
"Mole Relationships” Lab
Name _____________________________
I. Problem: Will lead (II) nitrate react with sodium iodide in a simple one to one ratio or is
there a better ratio that will balance the reaction?
II. Task: You are to imagine that you are employed by Sherwin-Williams to produce a yellow
stain that can be used in paint. You want to do it as cheaply as possible. You now know that
elements can combine in simple whole number ratios to form compounds. Such is the case in
the reaction of lead (II) nitrate with sodium iodide. This laboratory investigation will
demonstrate this fact and help you understand molar relationships in reactions and their
importance in the chemical production industry.
III. Hypothesis: Write the balanced reaction for this experiment and then predict
what ratio for lead (II) nitrate to react with sodium iodide to produce the maximum
amount of product.
IV. Procedure:
A. Place 5 small test tubes (all the same size) in a test tube rack and label them 1-5.
B. Using the labeled pipet and pipetter add the appropriate amount of lead (II) nitrate to
the test tubes as shown in table 1.
C. Then add the appropriate amount of sodium iodide to the test tubes as shown in table 1.
BE CAREFUL NOT TO LET THE PIPET TOUCH THE TEST TUBE OR ANY OTHER
SOLUTION. RETURN PIPET TO PROPER SLEEVE WHEN FINISHED.
D. Use a rubber stopper to mix each tube well.
E. Allow the test tubes to stand, undisturbed, for five minutes.
F. During these 5 minutes you can start on the analysis & conclusions below.
G. When the precipitate has all settled, make observations for your conclusions.
H. Clean and dry your test tubes as well as your lab area.
Test Tube
Test Tube
Test Tube
Test Tube
Test Tube
Solution
#1
#2
#3
#4
#5
Lead (II) Nitrate
1.50 mL
2.00 mL
3.00 mL
4.00 mL
4.50 mL
Sodium Iodide
4.50 mL
4.00 mL
3.00 mL
2.00 mL
1.50 mL
Ratio of Lead(II)
Nitrate to Sodium
Iodide
-over17
VI. Analysis & Conclusions:
1) Complete table 1 by identifying the ratios of the solutions in each tube.
2) Which of your test tube(s) had the largest amount of precipitate?______________
3) What was the lead nitrate to sodium iodide ratio for this tube?_______________
4) How does the balanced equation and its mole ratios compare to the ratio that you
found by experimentation?
If there were differing result than you would expect, why were the results different?
Do you accept or reject your hypothesis?
18
Crossing the Bridge Problems
(converting moles of one substance to moles of another)
Moles of “A” x coeff. of “B” = moles of “B”
coeff. of “A”
Balance each equation. Calculate the appropriate value (SHOW ALL WORK).
1. ___Ag + ___Cl2  ___AgCl
Type of reaction: ________________________________
If there are 5.0 moles of Ag needed to run this reaction, how many moles of Cl2 would also be needed?
__________.
This number of moles converts to how many grams of Cl2?
2.
___Fe(OH)3  ___Fe2O3 + ___ H2O
Type of reaction: ________________________________
If 6.0 moles of Fe(OH)3 produce Fe2O3 and water;
How many moles of Fe2O3 would be produced?_________________
How many moles of dihydrogen monoxide would be produced?_________________
How many grams of Fe(OH)3 were used in this example:
19
3. ___SiO2 + ____HF  ___SiF4 + ___H2O
Type of reaction:________________________________________
Molar ratios:
SiO2 to SiF4
SiF4 to H2O H2O to HF SiO2 to HF
25 moles of SiO2 converts to how many moles of SiF4? _____________________
How many grams of SiO2 ? _________________ How many molecules of SiF4?____________
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More Crossing the Bridge Problems
Moles of A to Moles of B
Show all work
1. Hydrogen and oxygen react under certain conditions to product water.
a. How many moles of hydrogen would be needed to produce 5.0 moles of water?
b. How many moles of oxygen would be needed to produce 5.0 moles of water?
2. Ethane, C2H6, can undergo combustion.
a. If 4.50 moles of ethane are available how many moles of carbon dioxide can be
produced?
b. If 4.50 moles of ethane are available how many moles of water can be made?
3. Sodium chloride is made from the synthesis of sodium and chlorine.
a. How many moles of sodium would it take to make 25.0 moles of sodium chloride?
b. How many moles of chlorine would it take to make 25.0 moles of sodium chloride?
21
4. Iron is generally produced from iron ore (Iron (III) oxide) through the reaction of the iron ore
with carbon monoxide in a blast furnace. Carbon dioxide is also a product in addition to the
iron.
a. If 456.2 grams of iron ore are available to react , how many moles of carbon
monoxide are needed?
b. Using the 456.2 grams of iron ore , how many moles of each of the products can be
made?
22
Stoichiometry Intro
Conversion of Grams to Grams
(FW is formula weight which is the same thing as molar mass)
Grams of A /FW = moles of A x coeff of B = moles of B x FW = Grams of B
coeff of A
1. ____Fe + ___S8  ___FeS
How many grams of Iron are required to make 86.7 grams of FeS?
How many moles of S8 are needed?
2. Carbon disulfide reacts with chlorine to produce carbon tetrachloride and disulfur dichloride. If 17.6 grams of
carbon disulfide are reacted with an excess of chlorine, how many grams of disulfur dichloride will result?
3.
White phosphorus (P4) is used in military missiles because it ignites (reacts with oxygen) spontaneously in
air to produce tetraphosphorus decoxide. How many grams of P4 will react with 25.0 grams of oxygen?
23
4.
8.36 x 1021 molecules of propane were combusted. How many grams of carbon dioxide were produced?
5. Aqueous sodium chloride is reacted with aqueous lead(II) nitrate. If the solution contains 65.7 g of sodium
chloride, how many grams of each product could be produced?
24
More Gram to Gram conversion problems
Calcium hydride and dihydrogen monoxide react to form calcium hydroxide and hydrogen.
If 51.7 grams of CaH2 react, then…
1. How many moles of calcium hydride would react?
2. How many grams of dihydrogen monoxide would react?
3. How many molecules of dihydrogen monoxide would react?
Balance the following equation and then answer the questions below the reaction
____CCl4 + ____O2
→
___CO2 + ___ Cl2
1. What is the molar ratio of CCl4 to Cl2?
2. How many grams of O2 will react with 25.6 grams of CCl4?
3. How many moles of O2 will react?
25
Stoichiometry Continues….
1. Tin (II) Fluoride is used in toothpaste and is produced by a single replacement reaction of tin with
hydrochloric acid.
a. Write the balanced chemical equation for this reaction.
b. What is the molar ratio of: HF to H2 ? _______________________
c. How many grams of tin (II) fluoride can be produced from 7.42 x1024 molecules of hydrofluoric acid?
2. Isopropyl alcohol (C3H7OH) burns in air according to the equation:
___C3H7OH + ___O2  ___CO2 + ___ H2O
a. What type of reaction is this?_________________________________
b. Calculate the number of moles of oxygen needed to react with 3.40 moles of C3H7OH.
3. Convert molecules to moles:
a. 18.06 x 1023 molecules = ________moles
b. 100.65 x 1025 molecules = _______moles
c. 3.55 x 1028 molecules = _______moles
26
4. Convert moles to grams:
a. 5.83 moles of Fe2O3 = ________grams
b. 6.11 moles of KAl(SO4)2 12H2O = _________grams
5. a. Write the balance chemical equation for the double replacement reaction of sodium phosphate with iron
(III) chloride
b. How many molecules of sodium chloride will be produced from 1.204 x 1025 molecules of iron (III) chloride?
27
28
Using Stoichiometry to Predict the Mass of a Product
Made in a Chemical Reaction
Problem:
What products will be formed in the following chemical reaction?
NaHCO3 (s) + HCl (aq) 
Can we predict how much product will form (grams) – if we know the grams of starting material?
Background:
NaHCO3 is sodium bicarbonate.
H2CO3 is carbonic acid and it decomposes into CO2 (g) and H2O (l).
Hypothesis:
Procedure:













Weigh a clean/dry 150 / 200 ml beaker. Record in table below.
Add 1.5 g of NaHCO3 to beaker. Reweigh. Record.
Add a couple of drops of HCl to the NaHCO3 beaker. Try not to let the drops touch – to reduce splattering.
Continue adding drops of HCl into the beaker until bubbling stops. (This will take several minutes)
As the liquid gets higher, gently swirl the beaker. Do not add acid while you swirl – to prevent splattering.
When you think the bubbling is done, confirm this by adding one more drop. Do not add an excess of acid.
Place beaker on ring stand set up.
Heat gently with a blue flame (no cone) – it should boil but not splatter.
Continue heating until product looks dry. This will take several minutes.
Cool.
Reheat for 3 minutes. Cool.
If it is not all the way dry - reheat again for 3 minutes. Cool.
Reweigh beaker + product. Record in table below.
Observations:
Starting Materials
Mass
grams
Empty 150 / 200 ml beaker
NaHCO3 (about 1.5 g)
-over-
29
Ending Materials
Mass
grams
Beaker + product
(must be dry!)
Empty 150 / 200 ml
beaker (from other table)
Grams of product only
Conclusions:
1. Based on the grams of starting material, use stoichiometry to calculate how many grams of product
should form (theoretical value):
2. Calculate % Yield:
% Yield =
Actual yield
----------------- x 100
Theoretical yield
Your % Yield = ___________ x 100
3. In a perfect experiment, the % yield value would be 100%. If yours is not 100%, give possible
reasons why (Be specific – do not just say Human Error).
30
(More)3 Stoichiometry
1. ___NaN3  ___Na + ___N2
a. What type of reaction is this? ______________________________
b. What is the molar ratio of N2 to NaN3 ? _________________
c. What is the formula weight (molar mass) of NaN3? _____________________
d. What is the formula weight (molar mass) of N2? __________________
e. 94.5 grams of NaN3 will result in how many grams of N2?
2. 4.88 x 1023 molecules convert to how many moles?
3. 10.51 moles of CuSO4 is equal to how many grams of CuSO4?
6. ___Cu + ___AgNO3  ___Cu(NO3)2 + ___ Ag
a. What type of reaction is this? _______________________________
b. 54.30 grams of AgNO3 will produce how many moles of Ag?
c. 54.30 grams of AgNO3 will produce how many moles of Cu(NO3)2?
d.
The answer to “6b” is equal to how many molecules of Ag?
e. The answer to “6c” is equal to how many grams of Cu(NO3)2?
31
32
Stoichiometry Problems: Moles to Mass, Mass to Moles
Remember, for each problem, you first need a correctly written and balanced equation. Show unit analysis and
proper sig figs.
1) A camping lantern uses the reaction of calcium carbide and dihydrogen monoxide to produce acetylene
gas (C2H2) and calcium hydroxide. You have 1.55 moles of calcium carbide and you need to know how
many grams of dihydrogen monxide to put in the lantern to completely use all the calcium carbide.
2) How many grams of potassium chlorate must decompose to produce potassium chloride and 1.45moles
of oxygen gas?
3) How many moles of solid copper must react with silver nitrate to produce 5.5 grams of solid silver and
copper(II) nitrate?
4) In a car battery, lead metal, lead (IV) oxide and sulfuric acid are reacted to produce lead(II) sulfate and
dihydrogen monoxide. You decide to try to make you own battery. You find that you have 45.2 grams
of Pb.
a. How many moles of lead (IV) oxide will you need?
b. How many moles of sulfuric acid will you need?
33
34
More Stoichiometry Problems!!
1) Sulfuric acid reacts with sodium hydroxide. Write the complete balanced equation for the
reaction.
a. Type of reaction _______________________________________
b. What is the molar ratio of sulfuric acid to sodium hydroxide? _________
c. If I want to make 5.00 moles of sodium sulfate, how many moles of sulfuric acid will I need
to start with?
d. If I make f 5.00 moles of sodium sulfate, how many grams of sodium sulfate will I have?
2.
___Na + ___Cl2  ___NaCl
a. Type of reaction ___________________________________
b. What is the formula weight (molar mass) of NaCl?
c. Determine the number of grams of NaCl that can be produced from 24.7 grams of Na.
d. How many molecules of NaCl will be produced?
3.
___C8H18 + ___O2  ___ CO2 + ____H2O
a. Type of reaction _____________________________________
b. What is the molar ratio of the reactants? __________________
c. What is the formula weight (molar mass) of C8H18?
d. If 27.3 grams of C8H18 (octane) are combusted, how many molecules of CO2 are
made?
35
4. Calcium will react with aluminum sulfide. Write the complete balanced equation for this
reaction.
a. Type of reaction _______________________________
b. If I have 2.568 x 1025 molecules of calcium, how many molecules of aluminum can I make?
c. 6.0 moles of aluminum sulfide will produce how many moles of calcium sulfide?
d. Using your answer from 4c, molecules of calcium sulfide would be produced?
36
Limiting Reactant/Reagent (L.R.):
In a reaction, many times the ratio of the reactants is not exactly in the same ratio as the
reaction calls for; one of the reactants may be present in extra amount to make sure the other
reactant is completely used up or to make the reaction go faster. When this occurs, the reactant
that is completely used up limits the amount of product(s) that can be produced and is thus called
the limiting reactant (L.R.). Once the all of the L.R. is used up, the reaction will stop and the
maximum amount of product(s) will have been produced. Because of this, there will also be left
over of the other reactant which will be called the excess reactant.
Analogy: You want to build cars with your Legos. You have 1,00 Lego bricks and 8 wheels. Each
car requires 40 Lego bricks and 4 wheels. The number of wheels is the “L.R.” because they will
limit how many cars you can build. There will be Lego bricks left over so they are the excess
reactant.
Ex) Given the following reaction, balanced the equation:
C3H8
+
5 O2

3 CO2
+
4 H2 O
If you start with 14.8 g of C3H8 and 3.44 g of O2,
a) determine the limiting reagent
b) determine the number of moles of carbon dioxide produced
c) determine the number of grams of H2O produced
d) determine the number of grams of excess reagent left over.
37
Limiting Reagents Worksheet
1. Given the following reaction, balance the equation:
Al2(SO3)3 +
NaOH 
Na2SO3
+
Al(OH)3
a) If 10.0 g of Al2(SO3)3 is reacted with 10.0 g of NaOH, determine the limiting reagent.
b) Determine the number of moles of Al(OH)3 produced
c) Determine the number of grams of Na2SO3 produced
d) Determine the number of grams of excess reagent left over in the reaction
2. Given the following reaction, balance the equation:
Al2O3
+ Fe  Fe3O4
+
Al
a) If 25.4 g of Al2O3 is reacted with 10.2 g of Fe, determine the limiting reagent
b) Determine the number of moles of Al produced
c) Determine the number of grams of Fe3O4 produced
38
3. Zinc and sulfur (S8) react to form zinc sulfide, write the balanced equation:
If 25.0 g of zinc and 30.0 g of sulfur are mixed,
a) Which chemical is the limiting reactant?
b) How many grams of zinc sulfide will be formed?
c) How many grams of the excess reactant will remain after the reaction is over?
4.
3.00 grams of Mg is ignited in 2.20 grams of pure oxygen to produce magnesium oxide
a. Which reactant is in excess?
b.
How much excess reactant is left over?
c. What mass of magnesium oxide is formed?
39
5. How many grams of aluminum sulfide are formed when 5.00 grams of aluminum is heated with
10.0 grams sulfur (S8)?
6. When MoO3 and Zn are heated together they react
3 Zn(s) + 2 MoO3(s)  Mo2O3(s) + 3 ZnO(s)
What mass of ZnO is formed when 20.0 grams of MoO3 is reacted with 10.0 grams of Zn?
40
Another Limiting Reagent Worksheet
1. Consider the following reaction:
3 NH4NO3 + Na3PO4 → (NH4)3PO4 + 3NaNO3
Answer these questions assuming we are starting with 30.00 grams of ammonium nitrate and 50.00
grams of sodium phosphate.
a. Which of the reactants is the limiting reagent?
b. What is the maximum amount of EACH product that can be formed?
c. How much of the “other” reagent is left over after the reaction is complete?
41
2.
Write the balance chemical equation for the reaction of calcium carbonate with iron(III) phosphate to
produce calcium phosphate and iron (III) carbonate.
Using your balanced chemical equation, answer these questions assuming we are starting with 100.00 grams of
calcium carbonate and 45.00 grams of iron (III) phosphate.
a. Which of the reactants is the limiting reagent?
b. What is the maximum amount of EACH product that can be formed?
c. How much of the “other” reagent is left over after the reaction is complete?
42
Stoichiometry, L.R., Empirical and Molecular Formula Practice:
1) Ninhydrin is a compound that reacts with amino acids and proteins to produce a dark-colored
complex. It is used by forensic chemists and detectives to see fingerprints that might
otherwise be invisible. Ninhydrin’s composition is 60.68% carbon, 3.40% hydrogen, and 35.92%
oxygen. What is the empirical formula for ninhydrin?
2) A hydrocarbon is found to contain 82.63% C and 17.37% H. It has a molar mass of 58.14g/mol.
a. Determine the molecular formula of this compound.
b. Write the balance equation for the combustion of this compound (molecular formula).
c. If 23.52g of this compound is combusted with 34.84g of oxygen, what mass of carbon
dioxide will be produced?
d. How many moles of water will be produced?
43
44
Stoichiometry Problems
Finish and balance the following reaction:
H2SO4
+
NaOH 
1) If I want to make 5.00 moles of sodium sulfate….
a) How many moles of sulfuric acid do I need?______
b) How many moles of sodium hydroxide do I need?_____
2) How many molecules of sodium sulfate can I make if I have:
a) 0.68 mole of sodium hydroxide.
b) 5.00 grams ofsulfuric acid.
c) 5.00 grams of sodium hydroxide.
d) 1.00 mole of sulfuric acid and 2.00 moles of sodium hydroxide.
e) 1.00 mole of sulfuric acid and 20.00 moles of sodium hydroxide.
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According to the following chemical equation (Finish and balance the synthesis reaction.)
Na
+
Cl2

1) How many moles of chlorine gas would react with 5.00 moles of sodium.
2) Determine the amount in grams and molecules of product that can be produced from
24.7 g sodium.
3) If there is 35.0 g sodium and 35.0 g of chlorine, which is the limiting reactant?
Write the balance chemical equation for the complete combustion of octane.
1) The ratio of volumes of oxygen gas reacted to carbon dioxide gas produced
is _________________. (coefficients also represent volume ratios)
2) If 27.3 g of octane are combusted, what mass of dihydrogen monoxide will be produced?
3) How many molecules of carbon dioxide will be produced from the 27.3 g of octane?
4) What is % mass of H in octane?
46
Percent Yield
Percent yield (% yield) is the actual (experimentally obtained) yield divided by the
theoretical (calculated) yield multiplied by 100.
1. An experiment was done in the lab reacting antimony and 98.60 grams of iodine. How many
grams of antimony (III) iodide would be expected to be produced? You collected 118.00
grams of SbI3 in the experiment you ran. What is the percent yield of SbI3?
___Sb + ___I2 
___SbI3
Actual grams of SbI3 ______________
Theoretical grams of SbI3 ______________
% yield = ______________________
2. ___Mg + ___HNO3  ___Mg(NO3)2 + ___H2
Type of reaction _____________________________
Bill Nye, the science guy uses 40.00 grams of magnesium and plenty of nitric acid to make
hydrogen gas (in grams). If 2.10 grams of hydrogen gas are actually produced, what is his percent
yield of hydrogen?
% yield = _________________
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3. Sodium bicarbonate decomposes to produce sodium hydroxide and carbon dioxide. Write
the balance chemical equation for this reaction.
If 47.72 grams of sodium bicarbonate are decomposed in the lab and 21.75 grams of sodium
hydroxide were actually made, what is the percent yield of sodium hydroxide?
% yield = ________________________________
4. Write the equation for the reaction of iron (III) phosphate with sodium sulfate to make
iron (III) sulfate and sodium phosphate.
If this reaction is performed using 65.45 grams of iron (III) phosphate and an excess of sodium
sulfate, what is the percent yield of iron (III) sulfate, if 66.00 grams of iron (III) sulfate are
actually produced in the lab?
% yield = ________________________________
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Limiting Reactant & Percent Yield
SHOW ALL WORK including units.
1.) Emily performed a reaction with benzene and its combustion with oxygen. She reacted 15.8
grams of benzene with 31.8 grams of oxygen (O2). How many grams of water (H2O) could
actually be produced? What is the limiting reactant?
2 C6H6
+
15 O2

6 H2O
+
12 CO2
Grams of water produced _________________
Limiting reactant _________________________
2.) Jon was performing an unauthorized experiment in the lab decomposing 58.2 grams of
potassium chlorate. Jon determined that there must have been 13.27 L of oxygen gas
produced in order for an explosion of that magnitude to occur. The oxygen gas would have a
density of 1.429 g/L at the temperature and pressure of this explosion. Jon, lying in his
hospital bed, wants you to determine the expected amount of oxygen and his percent yield of
oxygen?
KClO3

KCl +
O2
Expected grams of O2 produced_______________
Percent yield of O2 ____________________
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50
Making Aspirin (a L.R. and % yield lab problem)
Two students prepared aspirin according to the following reaction in which salicylic acid, C7H6O3, reacts with acetic
anhydride, C4H6O3, to form aspirin, C9H8O4, and acetic acid, HC2H3O2.
C7H6O3 + C4H6O3  C9H8O4 + HC2H3O2
Is the reaction balanced?
The reaction occurred in a flask and the aspiring crystals were removed by filtration. The aspirin crystals were transferred
to a watch glass to dry and then massed on the watch glass. The students’ grades are partially based on their lab technique
to obtain the best possible actual yield. Which student got the better grade and why? Use the information in each of the
students’ data tables below to determine who should receive the better grade.
Student #1
Mass of flask
Flask + C7H6O3
Volume of C4H6O3
Mass of watch glass
Watch glass + C9H8O4
37.820g
39.961g
5.01mL
22.744g
24.489g
Mass of flask
Flask + C7H6O3
Volume of C4H6O3
Mass of watch glass
Watch glass + C9H8O4
37.979g
40.010g
1.25mL
21.688g
23.236g
Student #2
1) Determine the molar masses of:
a. salicylic acid, C7H6O3 : ____________________
b. acetic anhydride, C4H6O3 :__________________
c. aspirin, C9H8O4 :_________________________
2) Determine the mass of salicylic acid, C7H6O3 used by each student:
Student 1____________________ Student 2_____________________
3) Given the density of acetic anhydride is 1.05g/mL, determine the mass of acetic anhydride, C4H6O3 used
by each student: (Show your work, Watch Sig. Figs.!)
Student 1____________________ Student 2_____________________
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4) What is the limiting reagent for each student? (Show your work, Watch Sig. Figs.!)
Student1:
Student 2:
5) What is the theoretical yield, in grams, of aspirin, C9H8O4, for each student (Show your work, Watch Sig. Figs.!)
Student 1:
Student 2:
6) What is the actual yield, in grams, of aspirin, C9H8O4, for each student?
Student 1____________________ Student 2_____________________
7) What is the %yield for each student? (Show your work, Watch Sig. Figs.!)
Student 1:
Student 2:
8) Who should get the better grade? Why?
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Limiting Reactant Lab Data Analysis Problem
Iron (III) chloride reacts with sodium hydroxide in solution to form solid iron (III) hydroxide and sodium chloride, which
remains in solution.
FeCl3 (aq) + 3 NaOH (aq) → Fe(OH)3 (s) + NaCl (aq)
If the reaction mixture starts with 50.00 g FeCl3 present and NaOH is added incrementally, the mass of solid Fe(OH)3
produced increases as more reaction occurs. The plot shown here is of mass Fe(OH)3 product as a function of mass of
NaOH added.
Mass Fe(OH)3 produced, grams
35,00
30,00
25,00
20,00
15,00
10,00
5,00
0,00
0,00
10,00
20,00
30,00
40,00
50,00
Mass of NaOH, grams
Answer the following questions in order to analyze this data.
1) Initially, 50.00 grams of iron (III) chloride is present. What amount is this in moles?
2) Consider the point on the plot where 10.00 g of NaOH have been added. What amount, in moles is this
3) a) Can the 10.00 g of NaOH consume all 50.00g of FeCl3 present? Yes or No (SHOW WORK)
b) Which is the limiting reactant at this point in the reaction (when 10.00 g rams of NaOH have been
added)? Explain how your answer.
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Mass Fe(OH)3 produced, grams
35,00
30,00
25,00
20,00
15,00
10,00
5,00
0,00
0,00
10,00
20,00
30,00
40,00
50,00
Mass of NaOH, grams
4) a) Now consider the reaction when 45.00 grams NaOH have been added. What amount of moles of
NaOH is this and what amount of FeCl3 in moles can be consumed by it.
b) Which is the limiting reactant at this stage, when 45.00 grams of NaOH have been added?
The reaction involves 3 moles of NaOH reaction with each mole of FeCl3. Because 0.3083 moles of FeCl3 are present,
three time that, 0.9249 moles are needed to consume all 50.00 grams of the FeCl3.
0.9249 moles is about 37 g of NaoH. So, when less than 37 grams of NaOH have been added, it is the limiting reactant.
When more than 37 grams of NaOH have been added, FeCl3 is the limiting reactant.
Mass Fe(OH)3 produced, grams
Limiting reactant is ____________
Limiting reactant is ____________
35,00
30,00
25,00
20,00
15,00
10,00
5,00
0,00
0,00
10,00
20,00
30,00
40,00
50,00
Mass of NaOH, grams
Explain how the trend line shows the L.R. and how you know when it changes.
54
Plop, Plop…Fizz, Fizz Lab
Limiting Reagent and Determination of NaHCO3 in Alka Seltzer Tablets
Introduction
The extent of a chemical reaction is determined by the amount of
reacting materials, or reactants, present in the reacting system.
Reagents are generally not mixed in exact amounts needed for the
reaction to take place; there is usually one of the reacting materials
added in excess. The excess reagent, usually a non-critical reagent
or an inexpensive material, is used to insure that the entire critical
reagent is used up so that there will be a maximum amount of
product formed. Also, an excess of one reactant can cause the
overall reaction to take place at a faster rate. Once the critical
reactant is used up, the reaction will stop. That critical reactant is
called the limiting reagent, that is, it is the reactant in the chemical
reaction that is used up first.
Alka Seltzer, and similar over-the-counter combination antacid and
pain relief medications, contain aspirin (acetylsalicylic acid), citric
acid, and NaHCO3 as the active ingredients. This medication is designed to be taken by dissolving it in
water before ingesting. When the tablet is placed in water, an acid-base reaction involving sodium
bicarbonate and the citric acid takes place resulting in the generation of carbon dioxide which is visible
by active bubbling of the mixture. The carbon dioxide, from the reaction, escapes into the atmosphere
and results in a weight loss from the total mass of the reactants. Using the loss in mass, one can
calculate the amount of sodium bicarbonate reacted, and determine the percent by mass of NaHCO3
contained in Alka Seltzer tablets.
In this experiment, the Alka Seltzer tablets will be reacted with differing amounts of acetic acid,
HC2H3O2, to produce the carbon dioxide. From the data, and graph of the data, the mass of the sodium
bicarbonate in the Alka Seltzer tablets can be calculated, and the identity of the limiting reagent can be
determined.
Translate the following word equation into a balanced chemical equation:
acetic acid + sodium bicarbonate
(vinegar)
 dihydrogen monoxide + carbon dioxide + sodium acetate
(in the Alka Seltzer)
Hypothesis (must discuss the L.R. for the experiment):
55
SAFETY
Goggles or safety glasses must be worn at all times in the laboratory
The chemicals used in this experiment do not pose any hazards. Vinegar (5% acetic acid) is not harmful,
however, in the event of skin contact, wash the affected area with water.
Do not drink any of the Alka Seltzer solutions or use any of the laboratory supplied tablets for medication.
Even if the tablets are sealed in foil wrappers, they cannot be assumed free of laboratory chemical
contamination.
PROCEDURE
1.
Obtain 8 Alka seltzer tablets.
2. Measure 35.0 mL of deionized water using a graduated cylinder and add it to a 250 mL beaker.
3. Weigh the beaker and water and record the mass.
4. Weigh and record the mass of an Alka Seltzer tablet.
5. Place the Alka Seltzer tablet into the 250 mL beaker that contains the water.
6. When the bubbling has ceased, use stir rod to stir the solution to ensure complete
dissolution of the tablet and to remove any visible bubbles of carbon dioxide. Gently tap the
stirring rod against the inside of the beaker to remove any drops of liquid before weighing
the beaker and its contents.
7. Weigh the beaker and its contents. Record the mass.
8. Dispose of the solution in the beaker as instructed. Wash the beaker and rinse it with deionized
water.
9. Repeat the experiment using 5.00 mL of acetic acid (vinegar) and 30.0 mL of water in the 250 mL
beaker.
NOTE: once the reaction has started, you may use a second 250-mL beaker to run the next
trial in the experiment. You can continue to alternate beakers, running the additional
experiments in simultaneous, but staggered trials. Be sure to keep track of the mass of each
beaker used, as the exact mass of each beaker is
different.
10. Repeat the experiment a third time using 10.0 mL acetic
acid (vinegar) and 25.0 mL of water in the 250 mL beaker.
11. Continue to repeat the experiment 5 more times increasing
the volume of the acetic acid by 5.0 mL and decreasing the
volume of water by 5.0 mL for each new trial as indicated in
Table 1.
56
Observations/Analysis:
Things to include in the observations/analysis section of lab report:
 Write the balanced chemical equation for the reaction of NaHCO3 (Alka Seltzer) and acetic acid.
 Calculate the mass of carbon dioxide generated for each of the trials (shown in the data table).
 Calculate the mass of acetic acid used for each trial using the density of acetic acid which
is 1.01 g/mL. (shown in the data table)
 Use grams of CO2 to calculate the mass of NaHCO3 reacted for each of the trials (stoichiometry;
show one sample calculation in your report).
 Calculate the average mass of NaHCO3 in the Alka Seltzer tablets and write it at the bottom of
the mass of NaHCO3 column of the data table..
 Use Microsoft Excel (graph instruction are given later in this lab) to plot the mass of reacted
NaHCO3 in each tablet versus the mass of acetic acid used. Remember, the independent variable
belongs on the x-axis. Draw a line-of-best-fit for the increasing points and another line-of-bestfit for the points that plateau. The point where the lines intersect will correspond your
experimental value for the average mass of NaHCO3 in an Alka Seltzer tablet. Compare this value
to your calculated average value from the data table.
 Using the average mass of NaHCO3 from the graph, calculate your % error for NaHCO3 given that
the company says the tablet actually contains 1.916 g in each tablet. (make sure to keep it
negative if your value is lower than the actual value). Show how you calculated this in your
report.
Conclusion:
Things to include in the conclusion section of lab report:
 Discuss your hypothesis and how the results proved or disproved your hypothesis.
 Using your graphed data, discuss the L.R. for the experiment trials and how you know that it is
the L.R..
 Discuss reasons why your calculated average mass of NaHCO3 (bottom of the data table) and the
value from the graph are different.
 Discuss in detail errors that would cause your % error to not be 0%. Be very specific when
describing your errors and why the error would cause your % to be over 0% or under 0%
Just saying human error is NOT a valid reason. You need to be specific as to what your error
actually was and how it would affect your results.
57
58
Experiment Volume of
Volume of
Mass of
Mass of
Total Mass Total Mass
Number
Acetic Acid
Water
Beaker
AlkaSeltzer before
after Rxn
(mL)
(mL)
and
Tablet (g)
(g)
Rxn (g)
Mass of
Mass of
Mass of
CO2 (g)
acetic acid
NaHCO3
added (g)
(g)
Liquids (g)
A
B
C
D
E
F
G
H
I
1
2
3
4
5
6
7
8
59
60
Alka Seltzer Lab Data Analysis:
Input data in Microsoft Excel
**You only need to input the mass of acetic acid and the mass of NaHCO3.
Highlight all the data.
Insert tab; scatter without a line.
Layout



tab will allow you to:
Insert chart and axis titles (include your name in the title)
Turn off legend
Turn on all gridlines (major and minor for both horizontal and vertical)
Chart location:
Design tab will allow you to change the chart location; choose separate sheet.
Change chart parameters
Layout tab:
Axes
Primary horizontal axis, more options (at the bottom)
 Min, fixed = 0
 Max, fixed= 40
 Major, fixed = 10
 Minor, fixed = 2
Primary vertical axis, more options (at the bottom)
 Min, fixed = 30
 Max, fixed = 70
 Major, fixed = 5
 Minor, fixed = 1
Subscripts:
Highlight text to be subscripted, right click, choose font, click on subscript
Add trendlines:
Design tab:
 Click on select data.
 Add new series
o Name it “trendline 1”
o X values: select acetic acid volumes that show an increase in mass of NaHCO3.
 Usually 0, 5, 10, 15ml
o Y values: select the mass of NaHCO3 that correspond to the selected x values.

Add new series
o Name it “trendline 2”
o X values: select the last acetic acid volume from the previous trendline and include all the rest of the
volumes.
 Usually 15, 20, 25, 30, 35 ml
o Y values: select the mass of NaHCO3 that corresponds to the selected x values.

Click o.k.
Two new sets of data points will be on the graph (different colors)
For each set right click on a data point → Add trendline, linear.
 For trendline 2 data series, forecast backward enough to cause the lines to cross (should be about 2 -4
units).
61
Completing a Lab Report
The steps to writing a lab report usually correspond to the scientific method.
Each step should be clearly marked.
I.
Problem or Purpose: Write a sentence describing the purpose or problem being
addressed by the lab experiment.
II.
Background Information: From your previous knowledge or from class notes or
computer research, state 2 or 3 sentences about relevant or helpful information
concerning the lab topic.
III.
Hypothesis: In your own words, make an educated guess about what you think is going
to happen in the lab exercise.
IV.
Procedure: A detailed list of lab equipment and chemicals should be made. Any special
techniques should be explained in this section. Pictures may be used to help clarify
assembly instructions. Sentences are not necessary.
V.
Observations/Analysis: Using sentences make statements of facts obtained from
experiment. Don’t use bullets. Can use tables, charts or graphs to show data but they
should be labeled appropriately.
VI.
Conclusions:
Answer any questions that were given with the lab. Write a summary paragraph. Write
4 or 5 sentences commenting on the results of the lab as compared to the results
expected from your hypothesis.
62
Alka Seltzer Lab Report Grade Sheet.
I.
II.
III.
IV.
V.
Problem/Purpose:
Background Information:
a. 2-3 sentences relevant to the lab topic.
Hypothesis
Procedure
a. Materials list (2)
b. Procedure steps (2)
______ (1)
______ (2)
Data/Analysis
a. Balanced chemical equation (1)
NaHCO3 + HC2H3O2  H2O + CO2 + NaC2H3O2
______(13)
_______(1)
_______(4)
b. Observations/Data table
i. Data table including calculated average mass of NaHCO3 (3)
ii. Include one example of how to calculate mass of NaHCO3 (2)
iii. % error calculation (show your work for this, it can be handwritten) (2)
c. Graph (5)
VI.
Conclusion
_______(8)
a. Discuss the average mass of NaHCO3 from data table and from graph
and why they are different. (1)
b. Discuss limiting reactant for the lab; what it is, when it changes,
and how you know which one is the limiting reactant (3)
c. Discuss hypothesis and if correct and why.(1)
d. Discuss your % error any errors (explain why it is not 0%) that occurred in the lab and why
and specifically how they have affected your experiment results. (3)
Remember, human error is not a valid error! Specifically describe your errors.
Proper format, used headings
_______(1)
Total_______/30
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