HS – Chemistry
Instructors: Janine Extavour and Marty Zatzman
Presenter: Namrta Bhardwaj
Limiting Reactants
Background Information
Prerequisite knowledge for this section should include nomenclature and balancing chemical equations.
It is also essential that students understand mole to mole and mass to mole calculation, which
incorporates their knowledge of the relationship between number of particles, moles and mass. It is
important that students understand the law of conservation of mass. Students should also be skilled in
using ratios and conversion factors in calculations.
Curriculum Expectations
Overall expectations:
D2. Investigate quantitative relationships in chemical reactions, and solve related problems
D3. Demonstrate an understanding of the mole concept and its significance to the quantitative analysis
of chemical reactions
Specific expectations:
D2.1 Use appropriate terminology related to quantities in chemical reactions, including, but not limited
to: stoichiometry, percentage yield, limiting reagent, mole, and atomic mass [C]
D2.5 Calculate the corresponding mass, or quantity in moles or molecules, for any given reactant or
product in a balanced chemical equation as well as for any other reactant or product in the chemical
reaction [AI]
D2.6 Solve problems related to quantities in chemical reactions by performing calculations involving
percentage yield and limiting reagents [AI]
D3.4 Explain the quantitative relationships expressed in a balanced chemical equation, using appropriate
units of measure (e.g., moles, grams, atoms, ions, molecules)
Place in the Curriculum
Strand B- Matter, Chemical Trends, And Chemical Bonding
Strand C- Chemical Reactions
Strand D - Quantities in Chemical Reactions
Strand E- Solutions and Solubility
Strand F- Gases and Atmospheric Chemistry
Placement of the Concept Within the Unit Chemical Quantities
Counting Atoms and Molecules:
The Mole
 The Avogadro Constant
and the Mole
 Molar Mass
Chemical Proportions in
Compounds
 Percentage Composition
 Empirical Formula of a
Compound
 Molecular Formula of a
Compound
Quantities in Chemical Reactions
 Stoichiometry
 Limiting Reactant
 Percentage Yield
HS – Chemistry
Instructors: Janine Extavour and Marty Zatzman
Presenter: Namrta Bhardwaj
Misconceptions / Learning Difficulties
1) When the mass of both reactants is given students are required to recognize that one of the
masses is limiting and the other mass is in excess. Students sometimes randomly select one of
the given masses as limiting or excess (or they assume that the masses are in the correct mole
ratios). Also, students assume the smaller mass is the limiting reagent.
Need to point out these are not trick questions
Important to stress the common steps i.e. in converting masses into amounts in moles in order
to relate to mole ratios in balanced equations.
Use demonstrations such as copper chloride reacting with different amounts of aluminum to
illustrate a mass to mole relationship
2) If reactants are in the same physical state the reaction reaches completion when both reactants
are totally converted
Sodium hydroxide solution and copper sulphate solution are combined in a beaker. Copper
hydroxide precipitate is formed. Carry out this reaction in different mole ratios the presence of
copper sulphate can be detected by its blue colour
3) If the reactants are in two different physical states (solid and liquid) the reaction reaches
completion when the entire solid is consumed.
Demonstrate this using different amounts of Mg reacting with HCl. Students will see that as the
amount of Mg is increase it no longer reacts since all of the HCl has been consumed.
4) Students have a limited view of the chemical system since they have been taught to consider a
reaction system as: reactants -> products
Need to rewrite equation so that excess reactants appear on the right hand side of the equation.
Reactants -> Products + excess reactant. Gizmo activity can be used to illustrate this.
Roadblocks:
1. Too much math
2. Ratios are a difficult concept
3. Each problem requires many steps which can be time consuming
Caution: this stuff is
difficult to follow at
first.
Be patient.
HS – Chemistry
Instructors: Janine Extavour and Marty Zatzman
Lesson Sequence
Day 1
Teaching Strategies
Presenter: Namrta Bhardwaj
Learning Styles (MI)
Take up homework
Review mass to mass
calculation
Teacher directed –
student participate
Visual, Auditory
(Logical/ Mathematical)
Use hot dogs and hot
dog bun analogy to
introduce concept of
limiting reactants
Discussion
Auditory
(Verbal/ Linguistic Logical/
Mathematical)
Demo- Na reacting with
large amount of water
Demo
Visual, Auditory (visual/
spatial)
Assessment
For learning
Homework check,
assess student’s
answers as homework
is being taken up
Exit pass: For the
reaction of copper
chloride and aluminum
which of the statements
is true and explain why:
Have students provide
alternative analogies
Think-pair-share
Auditory (Verbal/
Linguistic, Intrapersonal,
Interpersonal)
Equal masses of
reactants will react
completely in a
chemical equation.
Copper chloride and
Aluminum lab
Demo
Visual, Auditory (visual/
spatial, Logical/
Mathematical)
Chemicals react based
on mole ratios found in
a chemical equation.
Have students
brainstorm practical
reasons for having
limiting reactants
Discussion
Auditory
(Verbal/ Linguistic)
Chemicals react based
on mass ratios found in
a chemical equation.
Have students conduct
baking soda and vinegar
lab (or Mg and HCl) lab
Day 2
Solve sample problems
Provide students with a
flow chart to follow
Guided inquiry
Kinesthetic (kinesthetic,
visual/spatial)
Direct instruction
Visual, Auditory
(visual/ spatial, logical/
mathematical)
Start with balanced
chemical reaction that
has reactants in a 1:1
mole ratio
Progress to more
difficult sample
problems
Equal moles of
reactants will react
completely in a
chemical reaction.
For learning
3...2...1
3 things I know about
stoichiometry.....
2 things I am getting
better at......
1 thing I still need help
with......
HS – Chemistry
Instructors: Janine Extavour and Marty Zatzman
Presenter: Namrta Bhardwaj
Day 3
Extra practice
As learning and for
learning
Cooperative
grouping
Have groups display
answers on white
boards – gallery walk
Visual, Auditory
(visual /spatial, logical/
mathematical)
Day 4
Quiz on limiting and
excess reactants
Assess student’s
cooperative skills,
participation skills and
answers to questions
Of learning – mark quiz
Percent Yield
Calculations
Day 5
Direct Instruction
Conduct Limiting and
excess lab with percent
yield calculation
Guided inquiry
Visual, Auditory
(Logical/ Mathematical)
Of learning- collect and
mark lab
Visual, Kinesthetic (visual /
spatial, kinesthetic)
Supporting Diverse Student Needs
Challenge gifted students with questions such as: How many grams of a particular starting material will
remain at the end of a reaction?
Gifted students may figure stoichiometry out for themselves, given some appropriate starter questions.
Encourage them to develop their own methods for solving these problems rather than following a given
format.
ELL students who have difficulty understanding verbal explanations in class may benefit from writing out
the thought process used in solving sample problems.
Students that required more support may be giving more scaffolding and support in questions. Have
students make common sense prediction when solving problems.
HS – Chemistry
Instructors: Janine Extavour and Marty Zatzman
Presenter: Namrta Bhardwaj
Advanced Preparation
Day 1
Refer to Interactive Demonstrations for Mole Ratios and Limiting Reagents (annotated reference 1) and
prepare material for the lab accordingly.
Refer to How Big Is the Balloon? Stoichiometry Using Baking Soda and Vinegar (annotated reference 6)
and prepare material for the lab accordingly.
Day 5
Refer to pg 165 of the Nelson teacher’s resource for percentage yield in a chemical reaction lab and
prepare material for the lab accordingly.
Safety Considerations
 Remember to always wear safety goggles.
Reaction of Copper (II) chloride with Aluminum
 Copper(II) chloride is toxic by ingestion and irritating to skin
 Aluminum will also react with the solution to produce hydrogen gas. Flames should not be used
in this investigation.
Reaction of baking soda with vinegar
 Avoid getting baking soda or vinegar in eyes
Reaction of Na with water demo


Never use a piece of sodium larger than a ½ pea r.
The reaction should be carried out behind a clear safety barrier or at a distance from the
students.
Applications and Societal Implications
Careers in chemistry – Chemical Engineer
Cooking recipes, industrial reactions, prescription drug dosages, manufacturing, construction
The amount of carbon on earth is the ultimate limiting reagent for the number of people the earth
can have and in the sense that carbon is our "food"... the land area of the earth is a "limiting
reagent" that will limit our population before carbon does.....
L. H. Holmes Jr.
HS – Chemistry
Instructors: Janine Extavour and Marty Zatzman
Presenter: Namrta Bhardwaj
Annotated References:
Breyfogle, Bryan. (2006) Interactive Demonstrations for Mole Ratios and Limiting Reagents. Journal of
Chemical Education, 85 (5), 741.
The demonstration of the mole and mass ratios for the reaction of CuCl2 and Al were obtained from this
article.
Clyde, Dillard R. (1972) Two Lecture Experiments Demonstrating Limiting Quantities. Journal of
Chemical Education, 49 (12), A694.
Resource used for conducting limiting reactant experiment using Mg and HCl.
Gauchon, Laure, et al. (2007) Learning About Stoichiometry: From Students’ Preconceptions to the
Concept of Limiting Reactant . Chemistry Education Research and Practice, 8 (4), 362-375.
Article discusses many misconceptions that student encounter with studying limiting reactants.
Holmes, L. H. Jr. (1998) Limiting Reagent and Kinetics: Social Implications and Malthus' Prediction.
Journal of Chemical Education, 75 (8), 1004.
Interesting article that discusses food supply and land area in terms of limiting reagents.
Jenkins, Frank, et al. (2002). Chemistry 11. Toronto: Nelson. (course textbook)
Journal’s Editorial Staff (1997). How Big Is the Balloon? Stoichiometry Using Baking Soda and Vinegar.
Journal of Chemical Education, 74 (2), 1328A-1328B.
Article used for the Baking soda and vinegar lab.
Resource used for conducting limiting reactant experiment using vinegar and baking soda.
Kalanter, A.H. (1985) Limiting Reagent Problems Made Simple for Students. Journal of Chemical
Education, 62 (2), 106.
Article used to for the ICE method for solving limiting reactants.
Mustoe, Frank, et al. (2201). Chemistry 11. Toronto: McGraw-Hill Ryerson. (course textbook)
Websites:
http://www.chalkbored.com/lessons/chemistry-11.htm
good power point presentation on limiting/ excess reactants, also the chart method for solving limiting
reactant problems was taken from this site
http://www.youtube.com/watch?v=xk7PSpFC7NI&feature=related
demonstration of the flaming table and whoosh bottle
http://www.chemprofessor.com/
flow chart method was obtained from this site