𝐻2 + 𝑂2 −−→ 𝐻2 𝑂
How many grams of water will 5
grams of Oxygen produce?
5 grams of Hydrogen?
Tonight's Homework:
Finish Lab Report
pg 259 Numbers 2-10
Lab Report
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Purpose
Procedure
Data
Calculation (mass salt+dish)–(mass dish)
Results
Questions/Conclusion
www.pedagogics.ca
Limiting Reactant
Percent Yield
A Word About Mass
Conversions
• Calculating the mass-mass conversion
between compounds in a chemical
reactions is not something that will
disappear now that we are moving on
A Word About Mass
Conversions
• Calculating the mass-mass conversion
between compounds in a chemical
reactions is not something that will
disappear now that we are moving on
• If you can not calculate conversions from
mass-mass, mass –mole , mole-mole…..
A Word About Mass
Conversions
• Calculating the mass-mass conversion
between compounds in a chemical
reactions is not something that will
disappear now that we are moving on
• If you can not calculate conversions from
mass-mass, mass –mole , mole-mole…..
• You Will Fail
Consider the following reaction
2 H2 + O2  2 H2O
Reactants are combined in
perfect proportions
3 molecules
6 molecules
6 molecules
In reality this never happens
3 molecules
6 molecules
6 molecules
Consider
4 molecules
3 molecules
4 molecules +
leftover oxygen
Consider
LIMITING
REACTANT
EXCESS
REACTANT
Amount of
PRODUCT is
determined
by limiting
reactant
Consider
6 molecules
2 molecules
4 molecules +
leftover
hydrogen
Consider
EXCESS
REACTANT
LIMITING
REACTANT
Amount of
PRODUCT is
determined
by limiting
reactant
Given 24 grams of O2 and 5.0 grams of H2
determine the mass of H2O produced.
2 H2 + O2  2 H2O
the mass of H2O produced will be determined by the
limiting reactant - do TWO calculations
Two Calculations
Two Calculations
• Calculate the amount of product each reactant
would produce
Two Calculations
• Calculate the amount of product each reactant
would produce
• In this case convert grams of O2 to grams of H2O
Two Calculations
• Calculate the amount of product each reactant
would produce
• In this case convert grams of O2 to grams of H2O
• Then convert grams of H2 to grams of H2O
Two Calculations
• Calculate the amount of product each reactant
would produce
• In this case convert grams of O2 to grams of H2O
• Then convert grams of H2 to grams of H2O
• Whichever will produce the least amount
of water will be the limiting reactant
calculation for 24 grams of O2
24 g O2
32.0 g mol-1
2 H2O
1 O2
18.0 g mol-1
= 27 g of H2O
calculation for 24 grams of O2
24 g O2
32.0 g mol-1
2 H2O
1 O2
18.0 g mol-1
= 27 g of H2O
calculation for 5.0 grams of H2
5 g H2
2.0 g mol-1
2 H2O
2 H2
18.0 g mol-1
= 45 g of H2O
calculation for 24 grams of O2
24 g O2
32.0 g mol-1
2 H2O
1 O2
18.0 g mol-1
= 27 g of H2O
O2 is the LIMITING REACTANT and determines the
amount of product
calculation for 5.0 grams of H2
5 g H2
2.0 g mol-1
2 H2O
2 H2
18.0 g mol-1
= 45 g of H2O
H2 is the EXCESS REACTANT (some would be left
over)
How much hydrogen gas would be left over?
To calculate, first determine how much reacts
with all of the oxygen
How much hydrogen gas would be left over?
To calculate, first determine how much reacts
with all of the oxygen
given 24 grams of O2
24 g O2
32.0 g mol-1
2 H2
1 O2
3.0 g of H2 reacts so
2.0 g mol-1
= 3.0 g of H2
How much hydrogen gas would be left over?
To calculate, first determine how much reacts
with all of the oxygen
given 24 grams of O2
24 g O2
32.0 g mol-1
2 H2
1 O2
2.0 g mol-1
= 3.0 g of H2
3.0 g of H2 reacts so
5.0 g – 3.0 g = 2.0 g of hydrogen remains
Re-Cap
• What steps do you
take to convert the
mass of one
substance to the
mass of another in a
chemical reaction?
• What steps do you
take to determine
which substance will
be the limiting
reactant in a
reaction?
Percent Yield
Enoch the Red, an alchemist,
wants to try to turn lead into
gold (which you can’t do
chemically). He finds that
mixing lead with an
unidentified compound (gold
III chloride) actually produces
small amounts of gold. The
reaction is as follows:
2 AuCl3 +3 Pb  3 PbCl2 + 2 Au
Percent Yield
Enoch reacts 14.0 g of gold III
chloride with excess lead
metal. What would be the
maximum, THEORETICAL yield
of this reaction?
2 AuCl3 +3 Pb  3 PbCl2 + 2 Au
Percent Yield
Enoch reacts 14.0 g of gold III
chloride with excess lead
metal. What would be the
maximum, THEORETICAL yield
of this reaction?
2 AuCl3 +3 Pb  3 PbCl2 + 2 Au
Percent Yield
Enoch reacts 14.0 g of gold III
chloride with excess lead
metal. What would be the
maximum, THEORETICAL yield
of this reaction?
2 AuCl3 +3 Pb  3 PbCl2 + 2 Au
given 14.0 g of AuCl3
14.0 g AuCl3
303.5 g mol-1
2 AuCl3
2 Au
196.97 g mol-1
= 9.09 g Au
Percent Yield
Enoch recovers only 1.05 g of
gold from the reaction. This
could be for many different
reasons
some product was lost in the recovery process
the reaction did not go to completion
the AuCl3 is not pure
Percent Yield
the percentage yield expresses
the proportion of the expected
product that was actually
obtained.
actual
% yield=
×100%
theoretical
1.05
% yield=
×100%=11.6%
9.09
Baking Soda Lab
• In the baking soda lab, the formula for the
reaction should be :
• NaHCO3 + HCl ------> NaCl + CO2 + H2O
• Balance the equation
• Find the molar masses of
NaHCO3 & NaCl.
• Use the mass from you lab (mass baking
soda) to calculate theoretical yield of NaCl
• What do we need to calculate
the percent yield now that we
have the theoretical yield?
Lab Reports
• The discussion questions were designed
to have you calculate a theoretical yield
and calculate a percent yield from your
actual result.
Finding Limiting Reactant
• Determine the theoretical yield based on
the masses of each reactant
• Whichever produces the least amount is
your limiting reactant
Finding Theoretical Yield
• Use the mass-mass conversion from the
limiting reactant to the desired product
• The product produced by the mass of the
limiting reactant is the theoretical yield
Finding Percent Yield
• Use theoretical yield from your mass-mass
(gram-gram) calcualtions
• Make sure you have the correct limiting
reactant
• Divide the actual yield (given)
by the theoretical yield (from calculation)