Exam W 10/28

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Exam W 10/28

• Review T 10/27 1 pm

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Some Compounds with Empirical Formula CH2O
(Composition by Mass 40.0 C, 6.71 H, 53.3O)
Molecular M Formula
(g/mol) Name Use or Function
CH2O 30.03 Formaldehyde
Disinfectant Biological

preservative C2H4O2 60.05
Acetic acid Acetate polymers vinegar

( 5 solution) C3H6O3
90.08 Lactic acid Causes milk
to sour forms
in muscle
during exercise C4H8O4 120.10
Erythrose Forms during sugar

metabolism C5H10O5
150.13 Ribose Component of
many nucleic
acids and
vitamin B2 C6H12O6 180.16
Glucose Major nutrient for energy

in cells
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Two Compounds with Molecular Formula C2H6O
Property Ethanol
Dimethyl Ether
M (g/mol) 46.07
46.07 Color
Colorless
Colorless Melting point - 117oC
- 138.5oC Boiling point
78.5oC -
25oC Density (at 20oC) 0.789 g/mL
0.00195 g/mL Use
Intoxicant in In
refrigeration
alcoholic beverages
H H
H H H C C O
H H C O C H
H
H H
H
Table 3.4
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Molecular Formula
Molecules
Atoms
Avogadros Number
6.022 x 1023
Moles
Moles
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Chemical Equations
Qualitative Information
Reactants
Products
States of Matter (s) solid (l)
liquid (g) gaseous (aq) aqueous
2 H2 (g) O2 (g) 2 H2O (g)
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Chemical Equation Calculation - I
Atoms (Molecules)
Avogadros Number
6.02 x 1023
Molecules
Reactants
Products
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Chemical Equation Calculation - II
Mass
Atoms (Molecules)
Molecular Weight
Avogadros Number
g/mol
6.02 x 1023
Molecules
Reactants
Products
Moles
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• Stoichiometry
• The calculation of the quantities of reactants
  and products involved in a chemical reaction
• Interpreting a Chemical Equation
• The coefficients of the balanced chemical
  equation may be interpreted in terms of either
  (1) numbers of molecules (or ions or formula
  units) or (2) numbers of moles, depending on your
  needs.

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Information Contained in a Balanced Equation
Viewed in Reactants
Products terms of 2 C2H6 (g)
7 O2 (g) 4 CO2 (g) 6 H2O(g) Energy
Molecules 2 molecules of C2H6 7 molecules of
O2
4 molecules of CO2 6 molecules of
H2O Amount (mol) 2 mol C2H6 7 mol O2
4 mol CO2 6 mol H2O Mass (amu) 60.14 amu
C2H6 224.00 amu O2
176.04 amu CO2
108.10 amu H2O Mass (g) 60.14 g C2H6
224.00 g O2 176.04 g CO2 108.10 g H2O Total
Mass (g) 284.14g
284.14g
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• To find the amount of B (one reactant or product)
  given the amount of A (another reactant or
  product)

• 1. Convert grams of A to moles of A
• ? Using the molar mass of A
• 2. Convert moles of A to moles of B
• ? Using the coefficients of the balanced chemical
  equation
• 3. Convert moles of B to grams of B
• ? Using the molar mass of B

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• Propane, C3H8, is normally a gas, but it is sold
  as a fuel compressed as a liquid in steel
  cylinders. The gas burns according to the
  following equation
• C3H8(g) 5O2(g) ? 3CO2(g) 4H2O(g)
• How many grams of CO2 are produced when 20.0 g of
  propane is burned?

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Molar masses C3H8 3(12.01) 8(1.008) 44.094
g CO2 1(12.01) 2(16.00) 44.01 g
59.9 g CO2 (3 significant figures)
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• Limiting Reactant
• The reactant that is entirely consumed when a
  reaction goes to completion
• Once one reactant has been completely consumed,
  the reaction stops.
• Any problem giving the starting amount for more
  than one reactant is a limiting reactant problem.

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Figure 3.14 Limiting reactant analogy using
cheese sandwiches.
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• All amounts produced and reacted are determined
  by the limiting reactant.
• How can we determine the limiting reactant?
• Use each given amount to calculate the amount of
  product produced.
• The limiting reactant will produce the lesser or
  least amount of product.

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• Magnesium metal is used to prepare zirconium
  metal, which is used to make the container for
  nuclear fuel (the nuclear fuel rods)
• ZrCl4(g) 2Mg(s) ? 2MgCl2(s) Zr(s)
• How many moles of zirconium metal can be produced
  from a reaction mixture containing 0.20 mol ZrCl4
  and 0.50 mol Mg?

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ZrCl4 is the limiting reactant. 0.20 mol Zr will
be produced.
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• Urea, CH4N2O, is used as a nitrogen fertilizer.
  It is manufactured from ammonia and carbon
  dioxide at high pressure and high temperature
• 2NH3 CO2(g) ? CH4N2O H2O
• In a laboratory experiment, 10.0 g NH3 and 10.0 g
  CO2 were added to a reaction vessel. What is the
  maximum quantity (in grams) of urea that can be
  obtained? How many grams of the excess reactant
  are left at the end of the reactions?

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Molar masses NH3 1(14.01) 3(1.008) 17.02
g CO2 1(12.01) 2(16.00) 44.01
g CH4N2O 1(12.01) 4(1.008) 2(14.01)
1(16.00) 60.06 g
CO2 is the limiting reactant. 13.6 g CH4N2O will
be produced.
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To find the excess NH3, we find how much NH3
reacted
Now subtract the amount reacted from the starting
amount
10.0 at start -7.73 reacted 2.27 g remains
2.3 g NH3 is left unreacted. (1 decimal place)
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• Theoretical Yield
• The maximum amount of product that can be
  obtained by a reaction from given amounts of
  reactants. This is a calculated amount.

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• Actual Yield
• The amount of product that is actually obtained.
  This is a measured amount.
• Percentage Yield

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• 2NH3 CO2(g) ? CH4N2O H2O
• When 10.0 g NH3 and 10.0 g CO2 are added to a
  reaction vessel, the limiting reactant is CO2.
  The theoretical yield is 13.6 of urea. When this
  reaction was carried out, 9.3 g of urea was
  obtained. What is the percent yield?

Theoretical yield 13.6 g Actual yield 9.3 g
68 yield (2 significant figures)
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Figure 4.1 Reaction of potassium iodide solution
and lead (II) nitrate solution. Photo courtesy of
James Scherer.
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Figure 4.2 Motion of ions in solution.
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Figure 4.3 Testing the electrical conductivity
of a solution water.Photo courtesy of American
Color.
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Figure 4.3 Testing the electrical conductivity
of a solution sodium chloride.Photo courtesy of
American Color.
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Figure 4.4 Comparing strong and weak
electrolytes HCl. Photo courtesy of American
Color.
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Figure 4.4 Comparing strong and weak
electrolytes NH3. Photo courtesy of American
Color.
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Methanol
Li
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The Role of Water as a Solvent The Solubility
of Ionic Compounds
Electrical conductivity - The flow of electrical
current in a solution is a
measure of the solubility of ionic
compounds or a
measurement of the presence of ions in
solution. Electrolyte - A substance that
conducts a current when dissolved in
water. Soluble ionic compound
dissociate completely and
may conduct a large current, and are called
strong Eeectrolytes.
NaCl(s) H2O(l)
Na(aq) Cl -(aq)
When sodium chloride dissolves into water the
ions become solvated, and are surrounded by water
molecules. These ions are called aqueous and
are free to move through out the solution, and
are conducting electricity, or helping electrons
to move through out the solution
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Fig. 4.2
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The Solubility of Ionic Compounds in Water
The solubility of ionic compounds in water
depends upon the relative strengths of the
electrostatic forces between ions in the ionic
compound and the attractive forces between the
ions and water molecules in the solvent. There
is a tremendous range in the solubility of ionic
compounds in water! The solubility of so called
insoluble compounds may be several orders of
magnitude less than ones that are
called soluble in water, for example
Solubility of NaCl in water at 20oC 365
g/L Solubility of MgCl2 in water at 20oC 542.5
g/L Solubility of AlCl3 in water at 20oC 699
g/L Solubility of PbCl2 in water at 20oC 9.9
g/L Solubility of AgCl in water at 20oC 0.009
g/L Solubility of CuCl in water at 20oC 0.0062
g/L
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Precipitation Reactions Will a Precipitate Form?
If we add a solution containing potassium
chloride to a solution containing ammonium
nitrate, will we get a precipitate?
KCl(aq) NH4NO3 (aq) K(aq)
Cl-(aq) NH4(aq) NO3-(aq)
By exchanging cations and anions we see that we
could have potassium chloride and ammonium
nitrate, or potassium nitrate and
ammonium chloride. In looking at the solubility
table it shows all possible products as soluble,
so there is no net reaction!
KCl(aq) NH4NO3 (aq) No Reaction!
If we mix a solution of sodium sulfate with a
solution of barium nitrate, will we get a
precipitate? From the solubility table it shows
that barium sulfate is insoluble, therefore we
will get a precipitate!
Na2SO4 (aq) Ba(NO3)2 (aq)
BaSO4 (s) 2 NaNO3 (aq)
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The Solubility of Ionic Compounds in Water
The solubility of ionic compounds in water
depends upon the relative strengths of the
electrostatic forces between ions in the ionic
compound and the attractive forces between the
ions and water molecules in the solvent. There
is a tremendous range in the solubility of ionic
compounds in water! The solubility of so called
insoluble compounds may be several orders of
magnitude less than ones that are
called soluble in water, for example
Solubility of NaCl in water at 20oC 365
g/L Solubility of MgCl2 in water at 20oC 542.5
g/L Solubility of AlCl3 in water at 20oC 699
g/L Solubility of PbCl2 in water at 20oC 9.9
g/L Solubility of AgCl in water at 20oC 0.009
g/L Solubility of CuCl in water at 20oC 0.0062
g/L
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Precipitation Reactions Will a Precipitate Form?
If we add a solution containing potassium
chloride to a solution containing ammonium
nitrate, will we get a precipitate?
KCl(aq) NH4NO3 (aq) K(aq)
Cl-(aq) NH4(aq) NO3-(aq)
By exchanging cations and anions we see that we
could have potassium chloride and ammonium
nitrate, or potassium nitrate and
ammonium chloride. In looking at the solubility
table it shows all possible products as soluble,
so there is no net reaction!
KCl(aq) NH4NO3 (aq) No Reaction!
If we mix a solution of sodium sulfate with a
solution of barium nitrate, will we get a
precipitate? From the solubility table it shows
that barium sulfate is insoluble, therefore we
will get a precipitate!
Na2SO4 (aq) Ba(NO3)2 (aq)
BaSO4 (s) 2 NaNO3 (aq)
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Types of Chemical Reactions

• Most reactions fall under three basic types
• 1) Precipitation Reactions
• 2) Acid-Base Reactions
• 3) Oxidation-Reduction Reactions (RedOx)

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Precipitation
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Solubility

• Soluble ability to dissolve in a liquid
• Insoluble inability to dissolve in a liquid
• Not all Ionic Compounds are water soluble
• Not all molecular compounds are insoluble!

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Reactions Involving IonsMolecular vs. Ionic
Equations

• Chemical Reaction can be expressed by
• Molecular Equation (balanced chemical equation)
• Complete Ionic Equation (showing all ions in
  reaction)
• Net Ionic Equation (showing only those ions
  directly involved in reaction)
• Consider
• Copper (III) sulfate reacts with sodium hydroxide
  to form copper (III) hydroxide and sodium sulfate
  (all in water).

• Express reaction in molecular, complete ionic,
• and net ionic equations

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8 Simple Rules For Common Ionic Compounds
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Song For Solubility!!
(Taken from Cornell University Adapted by Daley
Sing to Rhythm of 99 Bottles) 
Potassium, sodium, and ammonium salts, 
Whatever they may be, Can always be depended
on For solubility.  Asked about the nitrates
or acetates The answer is always clear, They
each and all are soluble, Is all we want to
hear.  Most every chloride's soluble At least
we've always read Save silver, mercurous
mercury And (slightly) chloride of lead. Take
the Bromide and iodide salts There soluble as
can be Save silver, mercury, and lead That
precipitate as you see Every single sulfate Is
soluble ,  'Tis said 'Cept barium and
strontium And calcium and lead. 
Hydroxides of metals won't dissolve That is, all
but three Potassium, sodium and
ammonium Dissolve quite readily. And then you
must remember That you must not
"forgit" Calcium, barium, strontium Dissolve a
little bit.  The carbonates are insoluble, 
It's lucky that it's so, Or else, our marble
buildings Would melt away like snow.  (Repeat
with feeling)  Only note is that all Lithium
salts are Soluble too!!!
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Predicting Whether a Precipitation Reaction
Occurs Writing Equations
a) Calcium Nitrate and Sodium Sulfate solutions
are added together.
Molecular Equation
Ca(NO3)2 (aq) Na2SO4 (aq)
CaSO4 (s) 2NaNO3 (aq)
Total Ionic Equation
Ca2(aq)2 NO3-(aq) 2 Na(aq) SO4-2(aq)
CaSO4 (s) 2 Na(aq) 2 NO3-(aq)
Net Ionic Equation
Ca2(aq) SO-2(aq)
CaSO4 (s)
Spectator Ions are Na and NO3-
b) Ammonium Sulfate and Magnesium Chloride are
added together.
In exchanging ions, no precipitates will be
formed, so there will be no chemical reactions
occurring! All ions are spectator ions!
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Figure 4.6 Reaction of magnesium chloride and
silver nitrate. Photo courtesy of American Color.
Write molecular and ionic equations for this
reaction.
Ionic equation Ag(aq) Cl-(aq) ?AgCl(s)
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Oxidation-Reduction
2Na (s) Cl2(g)? 2NaCl(s)
Oxidation numbers
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Figure 4.10 Iron nail and copper ( II)
sulfate.Photo courtesy of American Color.
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Figure 4.10 Fe reacts with Cu2(aq) and
makesCu(s).Photo courtesy of American Color.
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Figure 4.10 The copper metal plates out on the
nail.Photo courtesy of American Color.
Write a net ionic equation for this reaction!
Cu2(aq) Fe(s) ? Cu(s) Fe2(aq)
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Acid-Base
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Definition of Acid Base

• Arrhenius
• Acid substance that produces H ions
• Base substance that produces OH- ions
• Bronsted Lowry
• Acid substance that donates a proton to another
  substances
• Base substance that accepts a proton to another
  substances

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Acids - A Group of Covalent Molecules Which Lose
Hydrogen Ions to Water Molecules in
Solution
When gaseous hydrogen iodide dissolves in water,
the attraction of the oxygen atom of the water
molecule for the hydrogen atom in HI is greater
that the attraction of the of the iodide ion for
the hydrogen atom, and it is lost to the water
molecule to form an hydronium ion and an iodide
ion in solution. We can write the hydrogen atom
in solution as either H(aq) or as H3O(aq) they
mean the same thing in solution. The presence of
a hydrogen atom that is easily lost in solution
is an Acid and is called an acidic solution.
The water (H2O) could also be written above the
arrow indicating that the solvent was water in
which the HI was dissolved.
HI(g) H2O(L) H(aq) I
-(aq)
HI(g) H2O(L) H3O(aq) I
-(aq)
H2O
HI(g) H(aq) I
-(aq)
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Figure 4.8B Red cabbage juice added to solutions
in the beakers.Photo courtesy of James Scherer.
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Molecular representation of ammonium hydroxide.
NH3(aq) H2O(l) ? NH4(aq) OH-(aq)
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Reaction of nitric acid with water.
HNO3(aq) H2O(l) ? NO3-(aq) H3O(aq)
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Figure 4.9 Reaction of a carbonate with an
acid.Photo courtesy of American Color.
Write the reaction thats occurring.
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Percent Yield/Limiting Reactant Problem - II
N2 (g) 3 H2 (g)
2 NH3 (g)
Solution Cont.
We have 3.066 moles of Nitrogen, and it is
limiting, therefore the theoretical yield of
ammonia is
2 mol NH3 1 mol N2
3.066 mol N2 x
6.132 mol NH3

(Theoretical Yield) 6.132 mol NH3 x
104.427 g NH3

(Theoretical Yield)
17.03 g NH3 1 mol NH3
Actual Yield Theoretical Yield
Percent Yield x
100
98.67 g NH3 104.427 g NH3
Percent Yield
x 100 94.49
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Molarity (Concentration of Solutions) M
Moles of Solute Moles Liters of
Solution L
M
solute material dissolved into the solvent In
air , Nitrogen is the solvent and oxygen, carbon
dioxide, etc.

are the solutes. In sea water , Water is the
solvent, and salt, magnesium chloride, etc.

are the solutes. In
brass , Copper is the solvent (90), and Zinc is
the solute(10)
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Fig. 3.11
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Preparing a Solution - I

• Prepare a solution of Sodium Phosphate by
  dissolving 3.95g of Sodium Phosphate into water
  and diluting it to 300.0 ml or 0.300 l !
• What is the Molarity of the salt and each of the
  ions?
• Na3PO4 (s) H2O(solvent) 3 Na(aq)
  PO4-3(aq)

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Figure 4.22C Titration of an unknown amount of
HCl with NaOH (3). Photo courtesy of American
Color.
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