Exam W 1028

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Exam W 10/28

• Review T 10/27 1 pm

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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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Leftover ammonia starting from urea

• 13.6 g urea 1 mol urea 2 mol NH3 17 g NH3
• 60.1 g urea 1 mol urea 1
  mol NH3
• 7.7 g NH3 used to make the 13.6 g urea
• Ammonia left 10.0 g 7.7 g used 2.3 g
  remaining

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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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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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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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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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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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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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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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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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