General Chemistry
Unit 12
(2013 – 2014)
 Stoichiometry
 Molar mass
 Molecules, Moles, Grams conversions
 Limiting Reagent
 % Yield
1
We are learning to:
1.
2.
Demonstrate an understanding of stoichiometry conversions (moles to moles, mass to mass, atoms/molecules to
atoms/molecules).
Identify the limiting reactant and use the limiting reactant to predict the amount of product produced.
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.
2
Stoichiometry
From 2 greek words:
Stoicheion = element
1792 – German Chemist
Metron = measure
Jeremias Benjamin Richter
Is concerned with the amount of substances involved in a reaction
Composition stoichiometry = mass relationships between elements in compounds
Ex: Na2SO4
2 Na / 1 SO4
Reaction stoichiometry = mass 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 ratio of hydrogen to oxygen =
2/1 or 2:1
The ratio of water to hydrogen =
2/2 or 1:1
3
Avogadro’s Number = Number of particles 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
or
the sum of all the atomic weights in the formula
Molar Mass Examples (to 2 decimal places)
1. NaCl = 22.99 + 35.45 = 58.44 g/mole
2. CuSO4  5H2O = 63.55 + 32.07 + 4(16.00) + 5(18.02)
= 159.62 + 90.10
= 249.72 g/mole
4
Calculate the Molar Mass for each of these compounds.
1.
KCl
2.
Li2SO4
3.
(NH4)2C2O4  H2O
4.
Potassium Hydroxide
5.
Copper (II) Bromide
6.
Magnesium Phosphate
7.
Trisilicon Heptoxide
5
Converting Moles to Grams
and
Converting Grams to Moles
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 in the space on the right. Report all answers to 2 decimal
places.
Work Space
__________ 1. 7.800 moles of Fe2O3
__________ 2. 100.2 moles of Pb(NO3)2
___________3. 1.22 moles of CO2 to grams
__________ 4. 120.8 grams of K2SO4 to moles
__________ 5. 4.60 grams of MgCl2 to moles
__________ 6. 2.300 grams of Ba3(PO4)2 to moles
6
Converting Moles to Molecules (particles or atoms)
And Back Again
1. 4.50 Moles of copper = ? Molecules of copper
2. 7.62 x 1024 Molecules of vanadium= ? Moles of vanadium
3. 91.20 Moles of sodium = ? Molecules of sodium
4. 3.01 x 1023 Molecules of fluorine= ? Moles of fluorine
5. 1345.9 Moles of iron = ? Molecules of iron
7
More Converting…
1.
1.806x 1024 molecules of Iron = ? grams
2.
1.20 x 1028 molecules of CuSO4 = ? grams
3.
380.84 grams of MgCl2 = ? molecules
4.
82.81 grams of Pb(NO3)2 = ? molecules
8
Moles And Compounds Worksheet
Directions: Write the answer to the problem on the blank provided. The correct setup must be to the right of the problem.
______________1. .738 moles of Fe2O3 to grams
______________2. 50.5 g of FeBr3 to moles
______________3. 1.51 x 10
23
molecules of Lead(II) iodide to moles
______________4. .445 moles of Carbon tetrachloride to molecules
______________5. .538 moles of Ce2(CO3)3 to grams
______________6. 150.4 g of Ce2(CO3)2 to moles
______________7. 7.22 x 10
25
molecules of CuCl2 · 4 H2O to moles
______________8. 1.45 moles of Pb(C2H3O2)2 to grams
______________9. 1.22 x 10
24
molecules of CO2 to grams
_____________10. 19.3 grams of H2O to molecules
9
Lab: Determining the Number of Moles and Molecules Used Up in a Burning
Candle
Purpose: to burn candle wax and to determine the number of moles and molecules of wax converted to
carbon dioxide and water.
Mass of plate____________g
Mass of candle and plate before burning:______________g
Mass of candle before burning:_____________________g
Light the candle and allow it to burn for 5 minutes. While it is burning, complete a-c below. Do NOT
play with the wax!
After 5 minutes, carefully blow out the candle.
Reweigh the candle
Mass of candle and plate after burning:________________g
Calculate the mass of candle wax burned:_______________g
Wax is a mixture of hydrocarbons. C25H52 can be used as a representative hydrocarbon in the mixture.
a) Write the equation for the burning (combustion) of wax below:
b) What 2 resources are used up as the candle burns?
c) What has happened to the atoms in these resources?
d) What is the molar mass of wax?_________________
e) How many molecules of wax were reacted during the burning?
f) How many moles of CO2 were produced?
g) How many gram of H2O were produced?
h) How many grams of O2 were reacted with the wax?
10
Crossing the Bridge Problems
Balance each equation. Calculate the appropriate value (SHOW ALL WORK).
Moles of A x
coeff of B = moles of B
------------coeff of A
1. ___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?
2.
___Fe(OH)3  ___Fe2O3 + ___ H2O
Type of reaction: ________________________________
If 6.0 moles of Fe(OH)3 produce Fe2O3 and water;
How many moles of Fe2O3 would be produced?_________________
How many moles of dihydrogen monoxide would be produced?_________________
How many grams of Fe(OH)3 were used in this example:
11
3. ___SiO2 + ____HF  ___SiF4 + ___H2O
Type of reaction:________________________________________
Molar ratios:
SiO2 to SiF4
SiF4 to H2O H2O to HF SiO2 to HF
25 moles of SiO2 converts to how many moles of SiF4? _____________________
How many grams of SiO2 ? _________________ How many molecules of SiF4?____________
12
Name _____________________________
"Mole Relationships” Lab
I. Problem: Will lead (II) nitrate combine 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:
IV. Procedure:
A. Place 5 small test tubes (all the same size) in a test tube rack and label them 1-5.
B. Using the labeled pipet and pipetor 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.
A. 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
1.5 mL
2 mL
3 mL
4 mL
4.5 mL
Sodium Iodide
4.5 mL
4 mL
3 mL
2 mL
1.5 mL
Ratio of Lead(II)
Nitrate to Sodium
Iodide
-over13
VI. Analysis & Conclusions:
1) Write the balanced reaction for this experiment:
2) Complete table 1 by identifying the ratios of the solutions in each tube.
3) Which of your test tubes had the largest amount of
precipitate?______________
4) What was the lead nitrate to sodium iodide ratio for this well?_______________
5) How does the balanced equation and its mole ratios compare to the ratio that you
found by experimentation? If there were differing result, why were the
results different? Do you accept or reject your hypothesis?
14
More Crossing the Bridge Problems
Moles of A to Moles of B
Show all work
1. Hydrogen and oxygen react under certain conditions to product water:
___H2 + ___ O2 → ___H2O
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:
___C2H6 + ___O2 → ___CO2 + ___ H2O
a. If 4.50 moles of ethane are available how many moles of CO2 can be produced?
b. If 4.50 moles of ethane are available how many moles of H2O can be made?
15
3. Sodium chloride is made from the synthesis of sodium and chlorine.
___Na + ___Cl2 → ___NaCl
a. How many moles of sodium would it take to make 25.0 moles of NaCl?
b. How many moles of chlorine would it take to make 25.0 moles of NaCl?
4. Iron is generally produced from iron are through this reaction in a blast furnace:
___Fe2O3 + ___CO → ___Fe + ___ CO2
a. If 456.2 grams of Fe2O3 are available to react , how many moles of CO are
needed? (Hint – grams of A to moles of B)
b. Using the 456.2 grams of Fe2O3 , how many moles of each of the product s can
be made?
16
Stoichiometry Intro
Conversion of Grams to Grams
Grams of A = moles of A x
coeff of B =
_________
------------
Molar Mass A
coeff of A
moles of B x Molar Mass B = Grams of B
1. ____Fe + ___S8  ___FeS
How many grams of Iron are required to make 86.7 grams of FeS?
How many moles of S8 are needed?
2. ___CS2 + ___Cl2  ___CCl4 + ___S2Cl2
If 17.6 grams of CS2 are reacted with an excess of Cl2, how many grams of S2Cl2 will result?
3.
___P4 + ___O2  ___P4O10
White phosphorus (P4) is used in military missiles because it ignites spontaneously in air. How many grams
of P4 will react with 25.0 grams of O2?
17
4. The combustion of propane (C3H8) produced 8.36 x 1021 molecules of CO2. How many moles of CO2
were produced?
___C3H8 + ___O2  ___
+ ___
5. What is the molecular weight of Vitamin B12?
The molecular formula = C63H84N14O14PCo.
18
More Gram to Gram conversion problems
___CaH2 + ___H2O
→
___Ca(OH)2 + ____H2
Molar Mass of H2O =
Molar Mass of CaH2 =
1. How many grams of H2O will react with 51.7 grams of CaH2?
2. How many molecules of H2O would react?
3. How many moles of CaH2 would that be equivalent to (51.7 grams)?
Balance the following equation and then answer the following questions.
____CCl4 + ____O2
→
___CO2 + ___ Cl2
Molar Mass of CCl4 =
Molar Mass of O2 =
1. How many grams of O2 will react with 25.6 grams of CCl4?
2. What is the molar ratio of CCl4 to Cl2?
3. How many moles of O2 will react?
19
Stoichiometry Continues….
1. Tin (II) Fluoride is used in toothpaste and made using the following reaction:
___Sn + ___HF  ___SnF2 + ___ H2
a. What is the molar ratio of: HF to H2 ? _______________________
b. What type of reaction is this? ______________________________
c. How many grams of SnF2 can be produced from 7.42 x1024 molecules of HF?
2. Isopropyl alcohol (C3H7OH) burns in air according to the equation:
___C3H7OH + ___O2  ___CO2 + ___ H2O
a. What type of reaction is this?_________________________________
b. Calculate the number of moles of oxygen needed to react with 3.40 moles of C3H7OH.
3. Convert molecules to moles:
a. 18.06 x 1023 molecules = ________moles
b. 100.65 x 1025 molecules = _______moles
c. 3.55 x 1028 molecules = _______moles
20
4. Convert moles to grams:
a. 5.83 moles of Fe2O3 = ________grams
b. 6.11 moles of KAl(SO4)2 12H2O = _________grams
5. ___Na3PO4 + ___FeCl3  ___NaCl + ____FePO4
a. Type of reaction?_____________________________
b. How many molecules of NaCl will result from 1.204 x 1025 molecules of FeCl3?
21
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 (grams) – if we know the grams 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.
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
grams
Empty 150 / 200 ml beaker
NaHCO3 (about 1.5 g)
-over22
Ending Materials
Mass
grams
Beaker + product
(must be dry!)
Empty 150 / 200 ml
beaker (from other 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 use Human Error).
23
(More)3 Stoichiometry
1. ___NaN3  ___Na + ___N2
a. What type of reaction is this? ______________________________
b. What is the molar ratio of N2 to NaN3 ? _________________
c. What is the Molar Mass of NaN3? _____________________
d. What is the Molar Mass of N2? __________________
e. 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?
24
4. ___Cu + ___AgNO3  ___Cu(NO3)2 + ___ Ag
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 “6b” is equal to how many molecules of Ag?
e. The answer to “6c” is equal to how many grams of Cu(NO3)2?
5. What is the Molar Mass of Na2B4O710H2O?
25
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.
1) A camping lantern uses the reaction of calcium carbide (CaC2) and water to produce acetylene gas
(C2H2) and calcium hydroxide. You have 1.55 moles of CaC2 and you need to know how many grams
of water to put in the lantern to completely use all the CaC2. Note, you are trying to conserve your
water to use for drinking.
2) How many grams of potassium chlorate (KClO3) must decompose to produce potassium chloride
(KCl) 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 (NO3-)?
4) In a car battery, lead metal, lead (IV) oxide (PbO2) and sulfuric acid (H2SO4) are reacted to produce
lead(II) sulfate (PbSO4) and water. You decide to try to make you own battery. You find that you
have 45.2 grams of Pb. How many moles of lead oxide and sulfuric acid will you need?
26
Stoichiometry Review Problems
1.
___H2SO4 + ___ NaOH  ___Na2SO4 + ___H2O
a. Type of reaction _______________________________________
b. If I want to make 5 moles of Na2SO4, how many moles of H2SO4 will I need to start
with?
c. What is the molar ratio of H2SO4 to NaOH? _________
d. If I make f 5 moles of Na2SO4, how many grams of Na2SO4 will I have?
2.
___Na + ___Cl2  ___NaCl
a. Type of reaction ___________________________________
b. What is the 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?
27
3.
___C8H18 + ___O2  ___ CO2 + H2O
a. Type of reaction _____________________________________
b. What is the molar ratio of the reactants? __________________
c. What is the Molar Mass of C8H18?
d. If 27.3 grams of C8H18 (octane) are combusted, how many molecules of CO2 are
made?
4.
___Ca +
___Al2S3

___Al
+
___CaS
a. Type of reaction _______________________________
b. If I have 2.568 x 1025 molecules of Ca, how many molecules of Al can I make?
c. 6.0 moles of Al2S3 will produce how many moles of CaS?
d. How many molecules of CaS are there?
28
Limiting Reagents Worksheet
1. Given the following reaction, balance the equation:
C3H8
+
O2
------->
CO2
+
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
2. Given the following reaction, balance the equation:
Al2(SO3)3 +
NaOH ------>
Na2SO3
+
Al(OH)3
a) If 10.0 g of Al2(SO3)3 is reacted with 10.0 g of NaOH, determine the limiting reagent.
b) Determine the number of moles of Al(OH)3 produced
c) Determine the number of grams of Na2SO3 produced
d) Determine the number of grams of excess reagent left over in the reaction
29
3. Given the following reaction, balance the equation:
Al2O3
+ Fe ------> Fe3O4
+
Al
a) If 25.4 g of Al2O3 is reacted with 10.2 g of Fe, determine the limiting reagent
b) Determine the number of moles of Al produced
c) Determine the number of grams of Fe3O4 produced
4. Zinc and sulfur react to form zinc sulfide, write the balanced equation:
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?
30
Another Limiting Reagent Worksheet
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?
Turn over
31
2.
Consider the following reaction:
3 CaCO3 + 2 FePO4
→ Ca3(PO4)2 + Fe2(CO3)3
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?
32
Stoichiometry Problems
Balance the following:
H2SO4
+
NaOH 
If I want to make 5 moles of Na2SO4:
How many moles of H2SO4 do I need?______
How many moles of NaOH do I need?_____
How many molecules of Na2SO4 can I make if I have:
1 mole of H2SO4 and 2 moles of NaOH
_____________mol Na2SO4
1 mole of H2SO4 and 20 moles of NaOH
_____________ mol Na2SO4
0.68 mole of NaOH
____________ mol Na2SO4
5 grams of H2SO4
_____________ g Na2SO4
5 grams of NaOH
_____________ g Na2SO4
33
According to the following chemical equation (Balance equation.)
Na
+
Cl2

1) How many moles of chlorine gas (Cl2) would react with 5 moles of sodium (Na)
2) Determine the amount in grams and molecules of product that can be produced from
24.7 g Na.
3) If there is 35.0 g Na and 35.0 g of Cl2, which is the limiting reactant?
In the reaction
C8H18 +
O2 
1. the ratio of volumes of O2 to CO2 is
_________________.
2. If 27.3g of C8H18 are combusted, what mass of water will be produced?
3. How many molecules of CO2 will be produced?
4. How many atoms of H are in 2 mol of C8H18?
34
Percent Yield
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. What is the percent yield of SbI3?
___Sb + ___I2 
___SbI3
Actual grams of SbI3 ______________
Theoretical grams of SbI3 ______________
% yield = ______________________
2. ___Mg + ___HNO3  ___Mg(NO3)2 + ___H2
Type of reaction _____________________________
Bill Nye, the science guy uses 40.00 grams of magnesium and plenty of nitric acid to make
hydrogen gas (in grams). If 2.10 grams of hydrogen gas are actually produced, what is his
percent yield of hydrogen?
% yield = _________________
35
3. ___NaHCO3  ___NaOH + ___ CO2
Type of reaction _________________________________
If 25.00 grams of carbon dioxide gas are produced in this reaction, how many grams of
sodium hydroxide should be produced? If 21.75 grams of sodium hydroxide were actually
made, what is the percent yield?
% yield = ________________________________
4. Write the equation for the reaction of iron (III) phosphate with sodium sulfate to
make iron (III) sulfate and sodium phosphate.
Type of reaction __________________________________
If this reaction is performed using 65.45 grams of iron (III) phosphate and an excess of
sodium sulfate, how many grams of iron (III) sulfate can be made? What is the percent yield
of iron (III) sulfate, if 66.00 grams of iron (III) sulfate are actually made?
% yield = ________________________________
36