Honors Chemistry
Unit 10
(2015-2016)
 Stoichiometry
 Molar mass
 % Composition
 Empirical and Molecular Formulas
 Molecules, Moles, Grams conversions
 Limiting Reagent
 % Yield
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
Metron = measure
1792 – German Chemist
Jeremias Benjamin Richter
Is concerned with the amount of substances involved in a reaction
Composition stoichiometry = relationships between elements in compounds
Ex: Na2SO4
2 Na / 1 SO4
Reaction stoichiometry = 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 coefficients can
represent moles as well as molecules).
The ratio of hydrogen to oxygen =
2 mole H2
1 mole O2
The ratio of water to hydrogen = 2 mole H2O
2 mole H2
or 1 mole H2O
1 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.
**Report all Molar Masses to 2 Digits After the
Decimal!!**
3
Complete all work for this page on a separate sheet of paper!
Calculate the Molar Mass for each of these compounds.
1. (NH4)2C2O4  H2O (this is a hydrate, you add the mass of the water to the molar mass of the compound)
2. Potassium Hydroxide
4. Magnesium Phosphate
3. Copper (II) Bromide
5. Trisilicon Heptoxide
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 using factor label method. Report all answers to
appropriate sig. figs. using the given moles or mass in the problem.
1) 7.800 moles of Fe2O3 is equivalent to how many grams?
2) What is the mass (in grams) of 100.2 moles of Pb(NO3)2?
3) 120.8 grams of K2SO4 is equivalent to how many moles?
4) Convert 4.6 grams of MgCl2 to moles.
Using Avogadro’s Number (6.02x1023 ): Converting Moles to Molecules (or particles or
atoms) And Back Again
1) 4.50 moles of NaCl is equivalent to how many molecules of NaCl?
2) Convert 6.62 x 1024 molecules of H2O to moles of H2O.
3) How many atoms of oxygen are present in 91.20 moles of CO2?
4) 4.87 x 1035 molecules of H2O contains how many atoms of hydrogen?
5) 2.36 grams of FeCl3 contains how many molecules of FeCl3 ?
Gram, Mole, and Molecule Conversions:
1) 1.806x 1024 atoms or iron is equivalent to how many grams of iron?
2) How many molecules of MgCl2 are present in 380.84 grams MgCl2?
3) 82.81 grams Pb(NO3)2 contains _____________ molecules of Pb(NO3)2
4) 37.6 grams H2SO4 contains how many atoms of oxygen?
25
5) How many moles are present in 7.22 x 10 molecules of CuCl2 · 4 H2O (this is a hydrate, you add the mass
of the water molecules to the molar mass of the compound)?
6) Convert 19.3 grams of Mg to atoms of Mg.
4
Percent Composition
Percent composition is the percent by mass that each element contributes to the entire molar
mass of a compound.
1) Find the molar mass of the compound.
2) Take the mass that the element contributed to the molar mass and divide by the molar
mass; multiply by 100 to get %.
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%
Work the following out on a separate sheet of paper.
#1-3, find the percent composition of for each of the elements in the following
compounds:
1) CuBr2
2) NaOH
3) (NH4)2S
4) % Barium in Ba(NO3)2
5) % Li in Li2O
6) % Phosphorus in Ca3(PO4)2
Using % composition to determine the grams of a particular element in a sample of a compound.
*you must first determine the % of the given element in the compound and then apply
that % to the given mass.
7) In 42.0 grams of MgO, how many grams of magnesium are there?
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?
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 __________
Continued
5
#9-11, determine the empirical formula with the given information in each problem.
9. A compound composed of 10.0% carbon (C), 58.6% chlorine (Cl) and 31.4% fluorine (F).
10. A compound composed of: 70.0% iron (Fe) and 30.0% oxygen (O)
11. A compound composed of: 101.18 g carbon (C) and 11.34 g hydrogen (H)
Empirical Formula Practice
Work the following out on a separate sheet of paper.
1) Determine the empirical formula of the compound made when 8.79 g of cobalt combines with
3.58 g of oxygen.
2) The composition of a compound is 40.0% sulfur and 60.0% oxygen by weight. What is its
empirical formula?
3) Pure formaldehyde consists of 40.00% carbon, 6.70% hydrogen, and 53.30% oxygen. What is
its empirical formula?
4) Determine the empirical formula of a compound that is 29.0% sodium, 40.6% sulfur, and 30.4 %
oxygen by weight.
5) A compound is composed of only nitrogen and oxygen. When 15.00 g of this compound
decomposes, it produces 4.57 g of nitrogen . Determine the empirical formula for this
compound.
6
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
7
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?
8
"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. Make
sure the test tubes are clean before you use them!
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
Continued
9
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 (II) 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?
10
Crossing the Bridge Problems
(converting moles of one substance to moles of another)
Moles of “A” x moles of “B” = moles of “B”
moles of “A”
mole ratio from the balanced
chemical equation (coefficients)
Balance each equation. Calculate the appropriate value (SHOW ALL WORK and Round for Sig. Figs.).
1. . ___SiO2 + ____HF  ___SiF4 + ___H2O
Molar ratios:
SiO2 to SiF4
SiF4 to H2O
Type of reaction:_______________________________
H2O to HF
SiO2 to HF
25 moles of SiO2 converts to:
a) how many moles of SiF4?
b) how many grams of SiO2 ?
c) How many molecules of SiF4?
2. ___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?
Continued 
11
3. ___Fe(OH)3  ___Fe2O3 + ___ H2O
Type of reaction: __________________________________
If 6.0 moles of Fe(OH)3 produce Fe2O3 and water;
a) How many moles of Fe2O3 would be produced?
b) How many moles of dihydrogen monoxide would be produced?
c) How many grams of Fe(OH)3 were used in this example:
More Crossing the Bridge Problems
Moles of A to Moles of B
Work the following out on a separate sheet of paper.
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?
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?
12
Stoichiometry: Intro. to Conversion of Grams of “A” to Grams of “B”
Grams of A x 1 mole of A x moles of B x grams of B
grams of A
moles of A 1 mole of B
molar
mass
mole
ratio
molar
mass
1. ____Fe + ___S8  ___FeS
a. How many grams of Iron are required to make 86.7 grams of FeS?
b. 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?
Continued 
13
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? (this requires 2 separate calculations)
14
More Gram to Gram conversion problems
Work the following out on a separate sheet of paper.
1. Calcium hydride and dihydrogen monoxide react to form calcium hydroxide and hydrogen.
If 51.7 grams of CaH2 react, then…
a. How many moles of calcium hydride would react?
b. How many grams of dihydrogen monoxide would react?
c. How many molecules of dihydrogen monoxide would react?
2. a. Balance the following equation and then answer the questions below the reaction
____CCl4 + ____O2
→
___CO2 + ___ Cl2
b. What is the molar ratio of CCl4 to Cl2?
c. How many grams of O2 will react with 25.6 grams of CCl4?
d. How many moles of O2 will react?
Stoichiometry Continues….
Work the following out on a separate sheet of paper.
1. Tin (II) Fluoride is used in toothpaste and is produced by a single replacement reaction of tin with
hydrofluoric 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. a. Write the balanced chemical equation for the combustion of Isopropyl alcohol (C3H7OH).
b.What type of reaction is this?
c. Calculate the number of moles of oxygen needed to react with 3.40 moles of C3H7OH.
3. Convert the following amount of molecules to moles:
a. 1.473 x 1024 molecules of CO2
b. 1.0065 x 1027 molecules H2O
c. 3.55 x 1028 molecules of NO2
4. Convert the following amount of moles to grams of the substance:
a. 5.83 moles of Fe2O3
b. 6.11 moles of Al2(SO4)3
5. a. Write the balance chemical equation for the double replacement reaction of sodium phosphate with iron
(III) chloride.
c. How many molecules of sodium chloride will be produced from 1.204 x 1025 molecules of iron (III)
chloride?
15
(More)3 Stoichiometry
Work the following out on a separate sheet of paper.
1) ___NaN3  ___Na + ___N2
a.
b.
c.
d.
e.
What type of reaction is this?
What is the molar ratio of N2 to NaN3 ?
What is the formula weight (molar mass) of NaN3?
What is the formula weight (molar mass) of N2?
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?
___Cu + ___AgNO3  ___Cu(NO3)2 + ___ Ag
4)
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 “4b” is equal to how many molecules of Ag?
e. The answer to “4c” is equal to how many grams of Cu(NO3)2?
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. Work the following out on a separate sheet of paper.
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?
16
More Stoichiometry Problems!!
Work the following out on a separate sheet of paper.
1) Sulfuric acid reacts with sodium hydroxide.
a. Write the complete balanced equation for the reaction.
b. What type of reaction is this?
c. What is the molar ratio of sulfuric acid to sodium hydroxide?
d. If I want to make 5.00 moles of sodium sulfate, how many moles of sulfuric acid will
I need to start with?
e. If I make f 5.00 moles of sodium sulfate, how many grams of sodium sulfate will I
have?
2)
___Na + ___Cl2  ___NaCl
a. What type of reaction is this?
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.
b.
c.
d.
What type of reaction is this?
What is the molar ratio of the reactants? __________________
What is the formula weight (molar mass) of C8H18?
If 27.3 grams of C8H18 (octane) are combusted, how many molecules of CO2 are made?
4) Calcium will react with aluminum sulfide.
a. Write the complete balanced equation for this reaction.
b. What type of reaction is this?
c. If I have 2.568 x 1025 molecules of calcium, how many molecules of aluminum can I
make?
d. 6.0 moles of aluminum sulfide will produce how many moles of calcium sulfide?
e. Using your answer from 4d, how many molecules of calcium sulfide would be
produced?
17
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.
18
Limiting Reagents Worksheet
Work the following out on a separate sheet of paper.
1. Balance the following reaction:
Al2(SO3)3 +
NaOH 
Na2SO3
+
Al(OH)3
If 10.0 g of Al2(SO3)3 is reacted with 10.0 g of NaOH, determine
a)
b)
c)
d)
the limiting reagent.
the number of moles of Al(OH)3 produced
the number of grams of Na2SO3 produced
the number of grams of excess reagent left over in the reaction
2. Balance the following reaction:
Al2O3
+
Fe 
Fe3O4
+
Al
If 25.4 g of Al2O3 is reacted with 10.2 g of Fe, determine
a) the limiting reagent
b) the number of moles of Al produced
c) the number of grams of Fe3O4 produced
3. Write the balanced chemical reaction for when zinc and sulfur, S8, react to form zinc
sulfide:
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.
Write the balanced chemical reaction for when magnesium reacts with oxygen to produce
magnesium oxide.
If 3.00 grams of Mg is ignited in 2.20 grams of pure oxygen to produce magnesium oxide
f. Which reactant is in excess?
g. How much excess reactant is left over?
h. What mass of magnesium oxide is formed?
5) How many grams of aluminum sulfide are formed when 5.00 grams of aluminum is heated
with 10.0 grams sulfur (S8)?
6) Using the following balanced chemical reaction: 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?
19
Another Limiting Reagent (reactant) Worksheet
Work the following out on a separate sheet of paper.
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?
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?
Stoichiometry, L.R., Empirical and Molecular Formula Practice:
Work the following out on a separate sheet of paper.
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?
20
Stoichiometry Problems (with L.R.)
Work the following out on a separate sheet of paper.
1) A) Finish and balance the following reaction:
H2SO4 + NaOH 
Using the reaction above,
B) If I want to make 5.00 moles of sodium sulfate, how many moles of sulfuric acid do I need?
C) If I want to make 5.00 moles of sodium sulfate, how many moles of sodium hydroxide do I
need?
D) How many molecules of sodium sulfate can I make if I have 0.68 mole of sodium hydroxide.
E) How many molecules of sodium sulfate can I make if I have 5.00 grams ofsulfuric acid.
F) How many molecules of sodium sulfate can I make if I have 5.00 grams of sodium hydroxide.
G) How many molecules of sodium sulfate can I make if I have 1.00 mole of sulfuric acid and 2.00
moles of sodium hydroxide.
H) How many molecules of sodium sulfate can I make if I have 1.00 mole of sulfuric acid and
20.00 moles of sodium hydroxide.
2) According to the following chemical equation (Finish and balance the synthesis reaction.)
Na
+
Cl2

A) How many moles of chlorine gas would react with 5.00 moles of sodium.
B) Determine the amount in grams and molecules of product that can be produced from
24.7 g of sodium.
C) If there is 35.0 g sodium and 35.0 g of chlorine, which is the limiting reactant?
3) A) Write the balance chemical equation for the complete combustion of octane.
B) What is the ratio of volumes of oxygen gas reacted to carbon dioxide gas produced?
(coefficients also represent volume ratios)
C) If 27.3 g of octane are combusted, what mass of dihydrogen monoxide will be produced?
D) How many molecules of carbon dioxide will be produced from the 27.3 g of octane?
E) What is % mass of H in octane?
21
Percent Yield
Percent yield (% yield) is the actual (experimentally obtained) yield divided by the
theoretical (calculated) yield multiplied by 100.
Work the following problems out on a separate sheet of paper:
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. A) What is the actual yield of SbI3 ? B) What is
the theoretical yield for SbI3 ? C) What is the percent yield of SbI3?
___Sb + ___I2  ___SbI3
2. Bill Nye, the science guy uses 40.00 grams of magnesium and plenty of nitric acid to make
hydrogen gas (in grams). A) What type of reaction is this? B) If 2.10 grams of hydrogen
gas are actually produced, what is his percent yield of hydrogen?
___Mg + ___HNO3  ___Mg(NO3)2 + ___H2
3. Sodium bicarbonate decomposes to produce sodium hydroxide and carbon dioxide.
A) Write the balance chemical equation for this reaction.
B) 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?
4. A) Write the equation for the reaction of iron (III) phosphate with sodium sulfate to
make iron (III) sulfate and sodium phosphate.
B) 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?
Limiting Reactant & Percent Yield
SHOW ALL WORK including units on a separate sheet of paper.
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). A) How many grams of water (H2O) could
actually be produced? B) What is the limiting reactant?
2 C6H6 (l)
+
15 O2 (g)

6 H2O
(g)
+
12 CO2 (g)
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 A) the expected amount of oxygen and B) his percent
yield of oxygen?
KClO3 (s) 
KCl (s) +
O2 (g)
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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.
24
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?
26
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 (mass) – if we know the mass 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. Add just enough until the reaction stops, no more bubbling when a drop is added.







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 (g)
Empty 150 / 200 ml beaker
NaHCO3
Continued
27
Ending Materials
Mass (g)
Beaker + product
(must be dry!)
Empty 150 / 200 ml
beaker (see other data
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). Explain carefully why your actual yield was either
higher or lower than the theoretical yield.
28