Hardware Models: Limiting
Reagents and Theoretical
Yields
Lab 6
Outline
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Reactions in Chemistry
Moles
Limiting Reagents
Theoretical Yield
Using Analytical Balances
Points of Interest
Next Assignment
Reactions in Chemistry
Reactions are complex
 Gases, solids and liquids all react
differently
 What you will be learning today are the
basics only
 Always work with balanced reactions
 Balanced reactions provide us with molar
ratios of reagents to products
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Moles
We cannot make direct comparisons in
chemistry using concentration or mass we use moles instead.
 A mole is 6.022 x 1023 of anything.
 This concept is similar to that of a dozen.
 We will be using the concept of a dozen
today since 6.022 x 1023 are too many
items to count out.
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Limiting Reagent
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A limiting reagent is the reagent you run out of
first in a reaction.
The reagent that is in excess is called, excess
reagent.
You must determine the limiting reagent of a
reaction before you can determine the
theoretical yield of product.
You will be limited by mass and number of items
in some of your questions today to demonstrate
this point.
Theoretical Yield
Theoretical yield is calculated to predict
how much product can be produced based
on the limiting reagent calculation.
 You will use your predicted masses
(theoretical values) to do your ratio
calculations today.
 After the theoretical yield is established,
and the actual yield obtained, one can
calculate percent yield.
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Using Analytical Balances
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Each balance auto-calibrates
Carefully open a door and make sure the basket is
fully hinged
Place a blue weigh boat on the basket
Close the door completely and without slamming it
Tare the boat
Add the hardware and close the door carefully
Record the mass to the closest 0.1 mg (0.0001 g)
Remove your hardware, close the door(s) carefully
and push the zero button
Points of Interest
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Collect the required pieces of hardware from
their containers.
Place these in a white plastic weigh boat.
The hardware may contain some oil. Wear
gloves if you don’t want oil on your hands.
Use the plastic weigh boat to carry your
hardware. It does not fit in the balance.
Use a blue plastic weigh boat in the balance to
weigh your hardware.
Small pieces get lost easily. Please keep track
of ALL your equipment.
Lab 7 Reminder
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Read the required reading sections in your textbook
and lab manual as you prepare for Lab 7.
 Go through the significant figure molar mass
tutorial in Blackboard before attempting the prelab questions.
 Use the periodic table in your lab manual.
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Complete and submit your pre-lab questions by the
deadline.
Study for the quiz.
Submit your Lab 6 Report at the start of next week’s
lab.
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