H o n o r r s s C h e m i i s s t t r r y
U n i i t t 1 1
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1

At the conclusion of this unit, the student will be able to:
1.
Demonstrate an understanding of stoichiometry conversions (moles to moles, mass to mass, atoms/molecules to atoms/molecules).
2.
Identify the limiting reactant and use the limiting reactant to predict the amount of product produced.
3.
Demonstrate an understanding of %mass (%composition).
4.
Demonstrate an understanding of empirical/molecular formulas.
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.
3a. Calculate the %mass (%composition) for each element in a compound.
4a. Use %composition to calculate the empirical formula for a compound given the elements present.
4b. Use the molar mass of the compound and the empirical formula to determine the molecular formula.
2

Stoichiometry
From 2 greek words:
Stoicheion = element Metron = measure
1792 – German Chemist Jeremias Benjamin Richter
Is concerned with the amount of substances involved in a reaction
Composition stoichiometry = mass relationships between elements in compounds
Ex: Na
2
SO
4
2 Na / 1 SO
4
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.
2H
2
+ 1O
2
 2H
2
O
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 10 23
602,000,000,000,000,000,000,000
(Named after Amadeo Avogadro – 1776-1856 Italian chemist and physicist)
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
1. NaCl = 22.99 + 35.45 = 58.44 g/mole
2. CuSO
4
 5H
2
O = 63.55 + 32.07 + 4(16.00) + 5(18.00)
= 159.62 + 90
= 249.62 g/mole
4

1. KCl
2. Li
2
SO
4
3. (NH
4
)
2
C
2
O
4

H
2
O
4. Potassium Hydroxide
5. Copper (II) Bromide
6. Magnesium Phosphate
7. Trisilicon Heptoxide
5

6

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. 7.8 moles of Fe
2
O
3
__________ 2. 100.2 moles of Pb(NO
3
)
2
___________3. 1.22 moles of CO
2
to grams
7

__________ 4. 120.8 grams of K
2
SO
4
to moles
__________ 5. 4.6 grams of MgCl
2 to moles
__________ 6. 2.3 grams of Ba
3
(PO
4
)
2
to moles
8

Converting Moles to Molecules (particles)
And Back Again
1. 4.50 Moles = ? Molecules
2.
6.62 x 10 24 Molecules = ? Moles
3.
91.20 Moles = ? Molecules
4.
3.01 x 10 23 Molecules = ? Moles
5.
1345.9 Moles = ? Molecules
9

23
4
28
2
3
2
10

Directions: Write the answer to the problem on the blank provided. The correct set-up must be to the right of the problem.
______________1. .738 moles of Fe
2
O
3
to grams
______________2. 50.5 g of FeBr
3
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 Ce
2
(CO
3
)
3
to grams
______________6. 150.4 g of Ce(CO
3
)
2
to moles
______________7. 7.22 x 10
25
molecules of CuCl
2
· 4 H
2
O to moles
______________8. 1.45 moles of Pb(C
2
H
3
O
2
)
2
to grams
______________9. 1.22 x 10
24
molecules of CO2 to grams
_____________10. 19.3 grams of H2O to molecules
11

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. C
25
H
52
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 CO
2 were produced? g) How many gram of H
2
O were produced? h) How many grams of O
2 were reacted with the wax?
12

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 + ___Cl
2

___AgCl
Type of reaction: ________________________________
If there are 5.0 moles of Ag needed to run this reaction, how many moles of Cl
2
would also be needed?
__________.
This number of moles converts to how many grams of Cl
2
?
2.
___Fe(OH)
3

___Fe
2
O
3
+ ___ H
2
O
Type of reaction: ________________________________
If 6.0 moles of Fe(OH)
3
produce Fe
2
O
3
and water;
How many moles of Fe
2
O
3 would be produced?_________________
How many moles of dihydrogen monoxide would be produced?_________________
How many grams of Fe(OH)
3
were used in this example:
13

3. ___SiO
2
+ ____HF

___SiF
4
+ ___H
2
O
Type of reaction:________________________________________
Molar ratios: SiO
2
to SiF
4
SiF
4
to H
2
O H
2
O to HF SiO
2
to HF
25 moles of SiO
2
converts to how many moles of SiF
4
? _____________________
How many grams of SiO
2
? _________________ How many molecules of SiF
4
?____________
14

Name _____________________________
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.
H.
Clean and dry your test tubes as well as your lab area.
Solution
Lead (II) Nitrate
Sodium Iodide
Ratio of Lead(II)
Nitrate to Sodium
Iodide
Test Tube
#1
1.5 mL
4.5 mL
Test Tube
#2
2 mL
4 mL
Test Tube
#3
3 mL
3 mL
Test Tube
#4
4 mL
2 mL
Test Tube
#5
4.5 mL
1.5 mL
-over-
15

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?
16

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:
___H
2
+ ___ O
2
→ ___H
2
O 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, C 2 H 6 , can undergo combustion:
___C 2 H 6 + ___O 2
→ ___CO 2 + ___ H 2 O 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 H 2 O can be made?
17

3. Sodium chloride is made from the synthesis of sodium and chlorine.
___Na + ___Cl 2
→ ___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:
___Fe 2 O 3 + ___CO → ___Fe + ___ CO 2 a. If 456.2 grams of Fe 2 O 3 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 Fe 2 O 3 , how many moles of each of the products can be made?
18

Grams of A / FW = moles of A x coeff of B = moles of B x FW = Grams of B
------------
1.
____Fe + ___S
8

___FeS coeff of A
How many grams of Iron are required to make 86.7 grams of FeS?
How many moles of S
8
are needed?
2. ___CS
2
+ ___Cl
2

___CCl
4
+ ___S
2
Cl
2
If 17.6 grams of CS
2
are reacted with an excess of Cl
2
, how many grams of S
2
Cl
2
will result?
3.
___P
4
+ ___O
2

___P
4
O
10
White phosphorus (P
4
) is used in military missiles because it ignites spontaneously in air. How many grams of P
4 will react with 25.0 grams of O
2
?
19

4.
The combustion of propane (C
3
H
8
) produced 8.36 x 10 21 molecules of CO
2
. How many moles of CO
2
were produced?
___C
3
H
8
+ ___O
2

___ + ___
5.
What is the molecular weight of Vitamin B12?
The molecular formula = C
63
H
84
N
14
O
14
PCo.
20

Formula weight of H
2
O =
More Gram to Gram conversion problems
___CaH
2
+ ___H
2
O → ___Ca(OH)
2
+ ____H
2
Formula weight of CaH
2
=
1. How many grams of H
2
O will react with 51.7 grams of CaH
2
?
2. How many molecules of H
2
O would react?
3. How many moles of CaH
2
would that be equivalent to (51.7 grams)?
21

Balance the following equation and then answer the following questions.
____CCl
4
+ ____O
2
→ ___CO
2
+ ___ Cl
2
Formula weight of CCl
4
=
Formula weight of O
2
=
1. How many grams of O
2
will react with 25.6 grams of CCl
4
?
2. What is the molar ratio of CCl
4
to Cl
2
?
3. How many moles of O
2
will react?
22

1. Tin (II) Fluoride is used in toothpaste and made using the following reaction:
___Sn + ___HF

___SnF
2
+ ___ H
2 a. What is the molar ratio of: HF to H
2
? _______________________ b.
What type of reaction is this? ______________________________ c.
How many grams of SnF
2
can be produced from 7.42 x10 24 molecules of HF?
2.
Isopropyl alcohol (C
3
H
7
OH) burns in air according to the equation:
___C
3
H
7
OH + ___O
2

___CO
2
+ ___ H
2
O a.
What type of reaction is this?_________________________________ b.
Calculate the number of moles of oxygen needed to react with 3.40 moles of C
3
H
7
OH.
3.
Convert molecules to moles: a.
18.06 x 10 23 molecules = ________moles b.
100.65 x 10 25 molecules = _______moles c.
3.55 x 10 28 molecules = _______moles
23

4.
Convert moles to grams: a. 5.83 moles of Fe
2
O
3
= ________grams b. 6.11 moles of KAl(SO
4
)
2

12H
2
O = _________grams
5.
___Na
3
PO
4
+ ___FeCl
3

___NaCl + ____FePO
4 a. Type of reaction?_____________________________ b. How many molecules of NaCl will result from 1.204 x 10 25 molecules of FeCl
3
?
24

What products will be formed in the following chemical reaction?
NaHCO
3
(s) + HCl (aq)

Can we predict how much product will form (grams) – if we know the grams of starting material?
NaHCO
3
is sodium bicarbonate.
H
2
CO
3
is carbonic acid and it decomposes into CO
2 (g)
and H
2
O
( l )
.

Weigh a clean/dry 150 / 200 ml beaker. Record in table below.

Add 1.5 g of NaHCO
3
to beaker. Reweigh. Record.

Add a couple of drops of HCl to the NaHCO
3
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.
Empty 150 / 200 ml beaker
NaHCO
3
(about 1.5 g)
25

Beaker + product
(must be dry!)
Empty 150 / 200 ml beaker (from other table)
Grams of product only
1.
Based on the grams of starting material, use stoichiometry to calculate how many grams of product should form (theoretical value):
2.
Calculate % Yield:
Actual yield
% 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).
26

3
1.
___NaN
3

___Na + ___N
2 a.
What type of reaction is this? ______________________________ b.
What is the molar ratio of N
2
to NaN
3
? _________________ c.
What is the formula weight of NaN
3
? _____________________ d.
What is the formula weight of N
2
? __________________ e.
94.5 grams of NaN
3
will result in how many grams of N
2
?
2.
What is the greek word for element? ____________________
3.
What is the greek word for measure? ___________________
4.
4.88 x 10 23 molecules convert to how many moles?
5.
10.51 moles of CuSO
4
is equal to how many grams of CuSO
4
?
27

6. ___Cu + ___AgNO
3

___Cu(NO
3
)
2
+ ___ Ag
a. What type of reaction is this? _______________________________ b.
54.30 grams of AgNO
3
will produce how many moles of Ag? c.
54.30 grams of AgNO
3
will produce how many moles of Cu(NO
3
)
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(NO
3
)
2
?
7. What is the formula weight of Na
2
B
4
O
7

10H
2
O?
28

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 (CaC
2
) and water to produce acetylene gas (C
2
H
2
) and calcium hydroxide. You have 1.55 moles of CaC
2 and you need to know how many grams of water to put in the lantern to completely use all the CaC
2
. Note, you are trying to conserve your water to use for drinking.
2) How many grams of potassium chlorate (KClO
3
) 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 (NO
3
)?
4) In a car battery, lead metal, lead (IV) oxide (PbO
2
) and sulfuric acid (H
2
SO
4
) are reacted to produce lead(II) sulfate (PbSO
4
) 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?
29

30

Stoichiometry Review Problems
___H
2
SO
4
+ ___ NaOH  ___Na
2
SO
4
+ ___H
2
O 1.
a. Type of reaction _______________________________________ b. If I want to make 5 moles of Na
2
SO
4
, how many moles of H
2
SO
4
will I need to start
with? c. What is the molar ratio of H
2
SO
4
to NaOH? _________ d. If I make f 5 moles of Na
2
SO
4
, how many grams of Na
2
SO
4
will I have?
2. ___Na + ___Cl
2
 ___NaCl a. Type of reaction ___________________________________ b. What is the formula weight 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?
31

3. ___C
8
H
18
+ ___O
2
 ___ CO
2
+ H
2
O a.
Type of reaction _____________________________________ b.
What is the molar ratio of the reactants? __________________ c.
What is the formula weight of C
8
H
18
? d.
If 27.3 grams of C
8
H
18
(octane) are combusted, how many molecules of CO
2
are
made?
4. ___Ca + ___Al
2
S
3
 ___Al + ___CaS a.
Type of reaction _______________________________ b.
If I have 2.568 x 10 25 molecules of Ca, how many molecules of Al can I make? c.
6.0 moles of Al
2
S
3
will produce how many moles of CaS? d.
How many molecules of CaS are there?
32

Percent Composition Problems
Find the percent composition of all of the elements in the following compounds:
1.
CuBr
2
Cu ________
Br________
2.
NaOH
Na________
O_________
H_________
3.
(NH
4
)
2
S
N_________
H_________
S_________
33

4.
% Barium in Ba(NO
3
)
2
5.
% Li in Li
2
O
6.
In 42.0 grams of MgO, how many grams of magnesium are there?
7.
In 75.5 grams of H
2
O, how many grams of hydrogen are there?
34

Mixed formulas
1.
Find the percentage composition of Cu
2
S
2.
As some salts crystallize from a water solution, they bind water molecules in their crystal structure. Sodium carbonate forms such a hydrate, in which 10 water molecules are present for every formula unit of sodium carbonate. Find the mass percentage of water in sodium carbonate decahydrate, Na
2
CO per mole.
3
•10H
2
O, which has a molar mass of 286.14 grams
3.
Magnesium hydroxide is 54.87% oxygen by mass. How many grams of oxygen are in 175 grams of magnesium hydroxide?
35

4.
Analysis of a 10.150 grams of sample of a compound known to only phosphorus and oxygen indicates a phosphorus content of 4.433 grams. What is the empirical formula of this compound?
5.
If 4.04 grams of Nitrogen combine with 11.46 grams Oxygen to produce a compound with a formula mass of 108.0 amu. What is the molecular formula of this compound?
36

Empirical Formulas from Composition
Example 1:
Determine the empirical formula of methane given that 6.0 g of methane can be decomposed into
4.5 g of carbon and 1.5 g of hydrogen.
Example 2:
Determine the empirical formula of the compound made when 8.65 g of iron combines with 3.72 g of oxygen.
Example 3:
The composition of a compound is 40% sulfur and 60% oxygen by weight. What is its empirical formula?
37

Example 4:
Pure formaldehyde consists of 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen. What is its empirical formula?
Example 5:
Determine the empirical formula of a compound that is 29.0% sodium, 40.5% sulfur, and 30.4 % oxygen by weight.
38

1.
Given the following reaction, balance the equation:
C
3
H
8
+ O
2
 CO
2
+ H
2
O
If you start with 14.8 g of C
3
H
8
and 3.44 g of O
2
, a) determine the limiting reagent b) determine the number of moles of carbon dioxide produced c) determine the number of grams of H
2
O produced d) determine the number of grams of excess reagent left
2.
Given the following reaction, balance the equation:
Al
2
(SO
3
)
3
+ NaOH  Na
2
SO
3
+ Al(OH)
3 a) If 10.0 g of Al
2
(SO
3
)
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 Na
2
SO
3
produced d) Determine the number of grams of excess reagent left over in the reaction
39

3.
Given the following reaction, balance the equation:
Al
2
O
3
+ Fe  Fe
3
O
4
+ Al a) If 25.4 g of Al
2
O
3
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 Fe
3
O
4
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?
40

5.
Which element is in excess when 3.00 grams of Mg is ignited in 2.20 grams of pure oxygen?
What mass is in excess? What mass of MgO is formed?
6.
How many grams of Al
2
S
3
are formed when 5.00 grams of Al is heated with 10.0 grams S?
7.
When MoO
3
and Zn are heated together they react
3 Zn(s) + 2 MoO
3
(s)  Mo
2
O
3
(s) + 3 ZnO(s)
What mass of ZnO is formed when 20.0 grams of MoO3 is reacted with 10.0 grams of Zn?
41

42

Another Limiting Reagent Worksheet
1.
Consider the following reaction:
3 NH
4
NO
3
+ Na
3
PO
4
→ (NH
4
)
3
PO
4
+ 3NaNO
3
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
43

2.
Consider the following reaction:
3 CaCO
3
+ 2 FePO
4
→ Ca
3
(PO
4
)
2
+ Fe
2
(CO
3
)
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?
44

Stoichiometry, L.R., Empirical and Molecular Formula Practice:
1) Ninhydrin is a compound that reacts with amino acids and proteins to produce a dark-colored complex. It is used by forensic chemists and detectives to see fingerprints that might otherwise be invisible. Ninhydrin’s composition is 60.68% carbon, 3.40% hydrogen, and 35.92% oxygen. What is the empirical formula for ninhydrin?
2) A hydrocarbon is found to contain 82.63% C and 17.37% H. It has a molar mass of
58.14 g/mol. a.
Determine the molecular formula of this compound. b.
Write the balance equation for the combustion of this compound (molecular formula). c.
If 23.52g of this compound is combusted with 34.84g of oxygen, what mass of carbon dioxide will be produced? d.
How many moles of water will be produced?
45

46

2
4

If I want to make 5 moles of Na
2
SO
4
:
How many moles of H
2
SO
4
do I need?______
How many moles of NaOH do I need?_____
How many molecules of Na
2
SO
4
can I make if I have:
1 mole of H
2
SO
4
and 2 moles of NaOH _____________mol Na
2
SO
4
1 mole of H
2
SO
4
and 20 moles of NaOH _____________ mol Na
2
SO
4
0.68 mole of NaOH ____________ mol Na
2
SO
4
5 grams of H
2
SO
4
_____________ g Na
2
SO
4
5 grams of NaOH _____________ g Na
2
SO
4
47

According to the following chemical equation (Balance equation.)
2

1) How many moles of chlorine gas (Cl
2
) 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 Cl
2
, which is the limiting reactant?
In the reaction
8
18
2

1.
the ratio of volumes of O
2
to CO
2
is _________________.
2.
If 27.3g of C
8
H
18
are combusted, what mass of water will be produced?
3.
How many molecules of CO
2
will be produced?
4.
How many atoms of H are in 2 mol of C
8
H
18
? What is % mass of H?
48

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 SbI
3 in the experiment you ran. What is the percent yield of SbI
3
?
___Sb + ___I
2
 ___SbI
3
Actual grams of SbI
3
______________
Theoretical grams of SbI
3
______________
% yield = ______________________
2.
___Mg + ___HNO
3
 ___Mg(NO
3
)
2
+ ___H
2
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 = _________________
49

3.
___NaHCO
3
 ___NaOH + ___ CO
2
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 = ________________________________
50

Limiting Reactant & Percent Yield
SHOW ALL WORK including units.
1.) Emily performed a reaction with benzene and its combustion with oxygen. She reacted 15.8
grams of benzene with 31.8 grams of oxygen (O
2
). How many grams of water (H
2
O) could actually be produced? What is the limiting reactant?
2 C
6
H
6
+ 15 O
2
 6 H
2
O + 12 CO
2
Grams of water produced _________________
Limiting reactant _________________________
2.) Jon was performing an unauthorized experiment in the lab decomposing 58.2 grams of
potassium chlorate. Jon determined that there must have been 1.327 x 10 4 mL of oxygen gas produced in order for an explosion of that magnitude to occur. Jon, lying in his hospital bed, wants you to determine the expected amount of oxygen and his percent yield of oxygen?
KClO
3
 KCl + O
2
Grams produced _________________
Percent yield ____________________
51

52

(a L.R. and % yield lab problem)
Two students prepared aspirin according to the following reaction in which salicylic acid, C
7
H
6
O
3
, reacts with acetic anhydride, C
4
H
6
O
3
, to form aspirin, C
9
H
8
O
4
, and acetic acid, HC
2
H
3
O
2
.
C
7
H
6
O
3
+ C
4
H
6
O
3
 C
9
H
8
O
4
+ HC
2
H
3
O
2
Is the reaction balanced?
The reaction occurred in a flask and the aspiring crystals were removed by filtration. The aspirin crystals were transferred to a watch glass to dry and then massed on the watch glass. The students’ grades are partially based on their lab technique to obtain the best possible actual yield. Which student got the better grade and why? Use the information in each of the students’ data tables below to determine who should receive the better grade.
Student #1
Mass of flask
Flask + C
7
H
6
O
3
37.820g
39.961g
Volume of C
4
H
6
O
3
Mass of watch glass
Watch glass + C
9
H
8
O
4
5.01mL
22.744g
24.489g
Student #2
Mass of flask
Flask + C
7
H
6
O
3
Volume of C
4
H
6
O
3
Mass of watch glass
Watch glass + C
9
H
8
O
4
37.979g
40.010g
1.25mL
21.688g
23.236g
1) Determine the molar masses of: a.
salicylic acid, C
7
H
6
O
3
: ____________________ b.
acetic anhydride, C
4
H
6
O
3
:__________________ c.
aspirin, C
9
H
8
O
4
:_________________________
2) Determine the mass of salicylic acid, C
7
H
6
O
3 used by each student:
Student 1____________________ Student 2_____________________
3) Given the density of acetic anhydride is 1.05g/mL, determine the mass of acetic anhydride, C
4
H
6
O
3
used by each student: (Show your work, Watch Sig. Figs.!)
Student 1____________________ Student 2_____________________
53

4) What is the limiting reagent for each student? (Show your work, Watch Sig. Figs.!)
Student1:
Student 2:
5) What is the theoretical yield, in grams, of aspirin, C
9
H
8
O
4
, for each student (Show your work, Watch Sig. Figs.!)
Student 1:
Student 2:
6) What is the actual yield, in grams, of aspirin, C
9
H
8
O
4
, for each student?
Student 1____________________ Student 2_____________________
7) What is the %yield for each student? (Show your work, Watch Sig. Figs.!)
Student 1:
Student 2:
8) Who should get the better grade? Why?
54

3
Introduction
The extent of a chemical reaction is determined by the amount of reacting materials, or reactants, present in the reacting system.
Reagents are generally not mixed in exact amounts needed for the reaction to take place; there is usually one of the reacting materials added in excess. The excess reagent, usually a non-critical reagent or an inexpensive material, is used to insure that the entire critical reagent is used up so that there will be a maximum amount of product formed. Also, an excess of one reactant can cause the overall reaction to take place at a faster rate. Once the critical reactant is used up, the reaction will stop. That critical reactant is called the limiting reagent, that is, it is the reactant in the chemical reaction that is used up first.
Alka Seltzer, and similar over-the-counter combination antacid and pain relief medications, contain aspirin (acetylsalicylic acid), citric acid, and NaHCO
3
as the active ingredients. This medication is designed to be taken by dissolving it in water before ingesting. When the tablet is placed in water, an acid-base reaction involving sodium bicarbonate and the citric acid takes place resulting in the generation of carbon dioxide which is visible by active bubbling of the mixture. The carbon dioxide, from the reaction, escapes into the atmosphere and results in a weight loss from the total mass of the reactants. Using the loss in mass, one can calculate the amount of sodium bicarbonate reacted, and determine the percent by mass of NaHCO
3 contained in Alka Seltzer tablets.
In this experiment, the Alka Seltzer tablets will be reacted with differing amounts of acetic acid,
HC
2
H
3
O
2
, to produce the carbon dioxide. From the data, and graph of the data, the mass of the sodium bicarbonate in the Alka Seltzer tablets can be calculated, and the identity of the limiting reagent can be determined.
SAFETY
Goggles or safety glasses must be worn at all times in the laboratory
The chemicals used in this experiment do not pose any hazards. Vinegar, 5% acetic acid, is not harmful, however, in the event of skin contact, wash the affected area with water.
Do not drink any of the Alka Seltzer solutions or use any of the laboratory supplied tablets for medication.
Even if the tablets are sealed in foil wrappers, they cannot be assumed free of laboratory chemical contamination.
PROCEDURE
1.
Obtain 8 Alka seltzer tablets.
2.
3.
4.
5.
Measure 35 mL of water into a 250 mL beaker using a graduated cylinder and add it to a
250 mL beaker.
Weigh the beaker and water and record the mass.
Weigh and record the mass of an Alka Seltzer tablet.
Place the Alka Seltzer tablet into the water in the 250 mL beaker.
55

6.
7.
8.
9.
When the bubbling has ceased, use stir rod to stir the solution to ensure complete dissolution of the tablet and to remove any visible bubbles of carbon dioxide. Gently tap the stirring rod against the inside of the beaker to remove any drops of liquid before weighing the beaker and its contents.
Weigh the beaker and its contents. Record the mass.
Dispose of the solution in the beaker as instructed. Wash the beaker and rinse it with deionized water.
Repeat the experiment using 5.00 mL of acetic acid (vinegar) and 30.0 mL of water in the
250 mL beaker.
NOTE: once the reaction has started, you may use a second 250-mL beaker to run the next trial in the experiment. You can continue to alternate beakers, running the additional experiments in simultaneous, but staggered trials. Be sure to keep track of the mass of each beaker used, as the exact mass of each beaker is different.
10.
Repeat the experiment a third time using 10 mL acetic acid (vinegar) and 25 mL of water in the 250 mL beaker.
11.
Continue to repeat the experiment 5 more times increasing the volume of the acetic acid by 5 mL and decreasing the volume of water by 5 mL for each new trial as indicated in Table 1.
Things to include in the analysis section of lab report:
 Write the balanced chemical equation for the reaction of NaHCO
3
(Alka Seltzer) and acetic acid.
(Hint: H
2
CO
3
will instantly form H
2
O and CO
2
.)
 Calculate the mass of carbon dioxide generated for each of the trials.
 Use grams of CO
2
to calculate the mass of NaHCO
3
reacted for each of the trials.
 Calculate the percent by mass of NaHCO
3
in each tablet of Alka Seltzer.
 Calculate the average percent of NaHCO
3
in the Alka Seltzer tablets.
 Use Microsoft Excel to plot the percent mass of the reacted NaHCO
3
in each tablet versus the volume of vinegar used. Draw a line-of-best-fit for the increasing points and another line-ofbest-fit for the points that plateau. The point where the lines intersect will correspond to the mass of NaHCO
3
in an average Alka Seltzer tablet. Compare this value to your calculated value.
Things to include in the conclusion section of lab report:
Discuss reasons why your calculated percent of NaHCO
3
and the value from the graph are different.
Discuss any other sources of error and how they might have affected your experiment.
56

8
7
6
5
3
2
4
Experiment
Number
Volume of
Acetic
Acid (mL)
A
1
Volume of
Water
(mL)
B
Mass of
Beaker and
Liquids (g)
C
Mass of
AlkaSeltzer
Tablet (g)
D
Total
Mass before
Rxn (g)
E
Total
Mass after Rxn
(g)
F
Mass of
CO
2
(g)
G
Mass of
NaHCO
3
(g)
H
% of
NaHCO
3
(%)
I
57

58

Completing a Lab Report
The steps to writing a lab report usually correspond to the scientific method.
Each step should be clearly marked.
I.
Problem or Purpose: Write a sentence describing the purpose or problem being addressed by the lab experiment.
II.
Background Information: From your previous knowledge or from class notes or computer research, state 2 or 3 sentences about relevant or helpful information concerning the lab topic.
III.
Hypothesis: In your own words, make an educated guess about what you think is going to happen in the lab exercise.
IV.
Procedure: A detailed list of lab equipment and chemicals should be made. Any special techniques should be explained in this section. Pictures may be used to help clarify assembly instructions. Sentences are not necessary.
V.
Observations: Using sentences make statements of facts obtained from experiment. Don’t use bullets. Can use tables, charts or graphs to show data but they should be labeled appropriately.
VI.
Conclusions:
Answer any questions that were given with the lab. Write a summary paragraph.
Write 4 or 5 sentences commenting on the results of the lab as compared to the results expected from your hypothesis.
59

Alka Seltzer Lab
I.
Problem/Purpose (1 pt):
Name:
II.
III.
Background Information (2 pts):
Hypothesis (1 pt):
IV.
Procedure: a.
Materials list (2 pts): b.
Procedure steps (3 pts):
V.
Data/Analysis: a.
Include balanced chemical equation (1 pt)
NaHCO
3
+ HC
2
H
3
O
2
 H
2
O + CO
2
+ NaC
2
H
3
O
2 b.
Data table including calculated %NaHCO
3
averages (4 pts) c.
Graph (5 pts) d.
Discuss L.R. – discuss what it is, what it means and then specifically on your graph – where and how do we know (3 pts)
VI.
Conclusion: a.
May discuss L.R. here instead of in analysis section b.
Discuss average %NaHCO3 from data table and from the graph and why they are different
(1 pt) c.
Calculate your % yield. Show your work for this – it can be hand written (2 pts) d.
Discuss how your results proved or disproved your hypothesis (1 pt.) e.
Discuss in detail any errors (why your % yield is not 100%) that occurred in the lab. Include
specifically how they have affected your results. (3 pts)
Remember, just saying human error is NOT a valid error! Specifically describe your errors.
Proper format and used headings, typed, font 12 (1 pt)
Total = 30 pts.
60