Transcript Stoichiometry Presentation (1)

Curriculum 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]
• D2.3 solve problems related to quantities in chemical reactions
by performing calculations involving quantities in moles,
number of particles, and atomic mass [AI]
• 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]
• D2.7 conduct an inquiry to determine the actual yield,
theoretical yield, and percentage yield of the products of a
chemical reaction (e.g., a chemical reaction between steel wool
and copper(II) sulfate solution), assess the effectiveness of the
procedure, and suggest sources of experimental error [PR, AI]
Lesson Sequence
Lesson 1: Introduction of the Mole Concept
Avogadro’s number
Lesson 2: Balancing Chemical Reactions
Lesson 3: Types of Stoichiometric Problems
 mass-mass, mass-volume, volume-volume
Lesson 4: The Limiting Reactant
Lesson 5: Percent Yield
 Calculate Actual and Theoretical Yields
Stoichiometry
Students will be able to :
Understand moles, mass, representative particles (atoms, molecules,
formula units), molar mass, and Avogadro’s number.
Determine the percent composition of an element in a compound.
Write balanced chemical equations: for example, for a given mass of
a reactant, calculate the amount of product produced.
Determine the limiting reactants: calculate the amount of product
formed when given the amounts of all the reactants present.
Calculate the percent yield of a reaction.
Introduction to Stoichiometry
Stoichiometry is the chemical term used to describe calculations
that allow us to find the amounts of chemicals involved in a given
reaction.
MINDS ON - Making S’mores
 In this “Minds On” activity students will be introduced to simple
stoichiometry.
 Each student will be given a small bag containing either gram
crackers, marshmallows or chocolate pieces
 Students will form groups of three and determine how many
s’mores can be made when they combine their bags of ingredients,
which ingredient is the limiting reactant, and which are in excess.
 Students will use a balanced recipe (equation):
2 Gc + 1 M + 4 Cp =
Gc2MCp4 ( or 1Sm)
Where: Gc = gram cracker
M = marshmallow
Cp = chocolate pieces
Sm = S’more
Balancing Equations and the Limiting Reactant
MINDS ON - Making S’mores continued:
 Students will complete this exercise that provides an
additional example of a balanced equation and a limiting
reagent using common materials.
 Students will be required to make-up their own example
of a balance equation and share it with a partner.
A balanced equation for making a S’more is:
2 Gc + 1 M + 4Cp
Gc2MCp4
…one can
make…
With…
…and…
30 M
excess Gc and
excess Cp
? Gc2MCp4
excess M and
excess Cp
30 Gc and
excess M
? Gc2MCp4
30 Gc
12 Cp
? Gc2MCp4
Unbalanced and Balanced Equations
 Students then apply the concept of balanced reactions to real
chemical equations.
H2 + Cl2  HCl
H2 + Cl2  2 HCl
H
Cl
Cl
H
H
H
H
Cl
(unbalanced)
reactants
H
Cl
2
2
H
H
Cl
Cl
Cl
(balanced)
products
1
1
Cl
reactants
H
Cl
2
2
products
2
2
Avogadro’s Number
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•
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A MOLE of any substance contains as many elementary units (atoms and
molecules) as the number of atoms in 12 g of the isotope of carbon-12.
This number is called AVOGADRO’s number NA = 6.02 x 1023 particles/mol
The mass of one mole of a substance is called MOLAR MASS symbolized by
MM, which can be found on the periodic table.
Units of MM are g/mol
Examples
H2
He
N2
O2
CO2
hydrogen
helium
nitrogen
oxygen
carbon dioxide
2.02
4.0
28.0
32.0
44.0
Consider a mole to be a collection
of atoms/molecules.
Here are some common collections
we use everyday and the numbers
of items in them.
g/mol
g/mol
g/mol
g/mol
g/mol
How Big is a Mole?
?
quadrillions
thousands
trillions
billions
millions
1 mole = 602213673600000000000000
or 6.022 x 1023
One mole of marbles would cover the entire Earth
(oceans included) for a depth of three miles.
One mole of $100 bills stacked one on top of another would
reach from the Sun to Pluto and back 7.5 million times.
It would take light 9500 years to travel from the
bottom to the top of a stack of 1 mole of $10 bills.
Stoichiometry Steps
1. Write a balanced equation.
2. Identify known & unknown.
3. Line up conversion factors and determine the:
Mole ratio moles  moles
Molar mass moles  grams
Molarity moles  liters soln
Molar volume moles  liters gas
Core step in all stoichiometry
problems!!
4. Use the mole ratio to calculate moles
5. Use molar mass to calculate grams
6. Check answer.
Stoichiometry - Problem Solving
 Students will apply their knowledge while working
in groups to solve a variety of questions involving
mole ratios and molar mass.
How many moles of KClO3 must decompose in
order to produce 9 moles of oxygen gas?
2KClO3  2KCl + 3O2
? mol
9 mol
x mol KClO3 = 9 mol O2
Mole
Ratio
2 mol KClO3
3 mol O2
= 6 mol KClO3
Stoichiometry Experiment
 Labs Experiment

Students will have the opportunity to perform a small experiment involving
Stoichiometry and Baking Soda(NaHCO3)
Students will:

calculate theoretical mass of NaCl based on a known mass of NaHCO3.

Experimentally determine the actual mass of NaCl produced.

Calculate the percent yield of the product.
Assessment

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
Students will write-up and submit lab report
Students will complete a worksheet with follow-up exercises
designed to assess their understanding of the concepts.
Assessed according to K/U, T/I, C achievement chart
Safety Consideration
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Remember to always wear safety goggles.
Tie back long hair
Wear gloves when dispensing acid
Follow established guidelines when working with Bunsen burners
Stoichiometry using Gizmo Activities

These interactive activities will allow students to learn how to balancing
chemical equations and determine the limiting reactant.

Students will simulate different types of chemical reactions. i.e.
combination, double displacement, decomposition.

Students will complete worksheet and submit for assessment
 Students will solve a variety of
stoichiometric problems that deal with real
world examples.
 Students will understand the importance of
stoichiometry in related areas such as
medicine, agriculture and space exploration.
Airbags

For an airbag to deploy an exact quantity of
nitrogen gas must be produced in an instant
2 NaN3(s)  2 Na(s) + 3 N2(g)
Fuels

How many grams of liquid oxygen would a rocket have to carry to
burn 10 kg of rocket fuel diborane completely?
Differentiated Assessment
 Prior to introducing stoichiometry, a diagnostic quiz will be administered testing
student knowledge on chemical bonding (both ionic and molecular) and chemical
reactions, as well as calculating percent, using ratios and applying algebra
(rearranging formulas, manipulating variables, solving for unknowns etc.)
 The students will be expected to hand in the Student Exploration Worksheet
associated with the Stoichiometry/Balancing Equations Gizmos Lab, which will be
marked for Knowledge and Understanding, and Thinking and Inquiry.
 Students will be assessed during the Stoichiometry and Baking Soda lab based on
their performance for communication. The follow-up worksheets based on this lab
will be marked for Knowledge and Understanding, as well as Application.
 Students will write one or two quizzes assessing the progress of their
understanding, including definitions, balancing equations and solving
stoichiometric problems.
 Students will be assessed daily on their oral responses during in class discussions.
 For summative assessment, students will write a unit test which will assess all
the learning skills and will include various definitions, lab results and all types of
stoichiometric problems (some with already balanced chemical equations, some
without), including determining empirical formulas, percent yield etc.
Potential Student Difficulties and Solutions
 Students may experience difficulty with the mathematics involved,
specifically with balancing equations and knowing how and when to
use stoichiometric formulas. Students will need to apply knowledge
of ratios to balance equations and algebra to solve stoichiometric
formulas.

Time should be spent reviewing these math concepts, as well as working
through various applicable problems to clarify the methodology, including
tips and tricks. Another method, particularly with solving stoichiometric
problems, is to teach students to not rely on formulas, but rather use
logic. The method of dimensional analysis can be taught to students
 Students may have problems understanding the concept of a mole and
Avogadro’s number.
 Explain the concept through the baker’s dozen analogy. A dozen is
to 12 units the same way a mole is to 6.022 x 1023 units, except that
a dozen is often a numerical term used to describe quantities of food,
such as muffins or eggs, while a mole is a numerical term used to
describe quantities in chemistry, such as atoms or molecules.
Potential Student Difficulties and Solutions cont.
 Students may also find the law of conservation of mass and balancing
equations challenging.
 Students may have difficulty with assigning coefficients to the chemical
compounds particularly when compound have more than one of the
same element (i.e. use subscripts).
 The Balancing Equations Gizmos Lab and the S’Mores and weightbalance analogies along with clear definitions and examples may
help clarify any misunderstandings as well as clarify various other
questions that may arise. Various methods for solving balancing
equation problems may also be introduced like trial and error, or
mathematical ratios and charts.
Annotated References
 Mortimer, C.E. (1978). Chemistry: A Conceptual Approach. D. Van Nostrand Company,
New York.
This book was used primarily as a source of background information on stoichiometry, the
law of conservation of mass, moles, chemical equations etc. Although the material
presented in this textbook is a brief and not well-explained, it is an excellent resource to
refresh a teacher’s understanding of general chemistry, as well as offers some excellent,
systematically and clearly solved examples, as well as an abundance of practice questions for
students.
 We found these websites useful:
 Balancing Chemical Equations Gizmo.
http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=
408
 Chemistry: Stoichiometry lesson plans/ideas.
http://www.unit5.org/chemistry/stoichiometry.html