3/24/2014

Today:
◦ Types of Chemical Reactions:

 Double Replacements:
 Precipitations: Electrolytes vs.
NONelectrolytes
 Acid-Base Neutralizations
 Solution Stoichiometry & Titrations
EXAM 2 Next Meeting:
◦ Bring GREEN SCANTRON
◦ Check out study guide, practice
problems & answer keys on
Canvas
 Redox Reactions:




Combustions
Single Replacement Reactions
Decompositions
Synthesis Reactions
iClicker Participation Question:
Calculating Percent Yield BASED ON LIMITING REAGENT
20 moles of iron (III) oxide is mixed with 15 moles of
aluminum metal but only 10 moles of iron
metal is produced as a product.
A. 75 %
What is the percent yield of the reaction?
B. 67 %
Fe2O3 + 2 Al
2 Fe + Al2O3
C. 50 %
D. 25 %
E. 12.5 %
Chemical Reactions
“The water a cow drinks turns to milk;
the water a snake drinks turns to poison.”
—Basho, Poet of Japan (1694)
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"It’s amazing that the body feeds the
brain sugar and amino acids and what
comes out is poetry and pirouettes.“
--Neurologist Robert Collins
Double Replacements:
Types of Reactions
Neutralizations & Precipitations
Redox Reactions:
Combustions
Single Replacements
Decompositions
Reactions can be grouped
into general categories.
Each category follows a
pattern that can be used
to predict the possible
products & outcomes of
the chemical reaction in
question.
Synthesis
Double Replacement Reactions
Double Replacement: a reaction where two SIMILAR groups
switch positions.
This most often occurs when two ionic compounds react to
form two new compounds by simply trading cations.
In order for a double replacement reaction to actually occur,
one of the products must NOT be aqueous – a PRECIPITATE
must form for the reaction to occur.
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1. PREDICT the products of the double replacement reaction.
2. BALANCE the equation.
3. Use the SOLUBILITY GUIDELINES to predict the phase of each
component in the reaction.
3. Use the SOLUBILITY GUIDELINES to predict the phase of each
component in the reaction.
3. Use the SOLUBILITY CHART to predict the phase of each
component in the reaction.
AFTER mixing the solutions,
but BEFORE any reaction occurs
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3. Use the SOLUBILITY CHART to predict the phase of each
component in the reaction.
AFTER reaction occurs &
PRECIPITATE FORMS
Strong Electrolytes: CONDUCT ELECTRICITY
due to the presence of dissolved ions
NONElectrolytes: DO NOT conduct
electricity → No dissolved ions present
Water treatment
plants often use
precipitate reactions
to remove toxic
heavy metals from a
water supply.
This reduces the level
of dissolved metal
ions to an acceptable
levels by converting
most of the metal to
its insoluble form.
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iClicker Participation Question:
General Solubility Guidelines
A. AgOH(s)
Based on the observations below, what is the likely
identity of the precipitate in the first reaction?
AgNO3(aq) + K2Cr2O7(aq) → PRECIPITATE FORMS
HNO3(aq) + KOH(aq) → NO PRECIPITATE FORMS
B. Ag2Cr2O7(s)
C. KNO3(s)
D. H2Cr2O7(s)
E. NO3Cr2O7(s)
Solution Stoichiometry
Instead of using grams to find the moles of a component:
Volume and Molarity can be used to determine MOLES
& this information can be worked into stoichiometry
problems.
2 AgNO3 + K2Cr2O7 → Ag2Cr2O7 + KNO3
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iClicker Participation Question:
Solutions & Concentration: Volume x Molarity = Moles of Solute
A. 12.5 mL
B. 25 mL
C. 50 mL
D. 125 mL
Consider an aqueous solution of sodium carbonate
with a concentration of 5 M. What volume of solution
would be needed to supply 0.25 moles of Na2CO3?
Concentration ALONE
does not specify how
much solute is present.
1M=
𝟏 𝒎𝒐𝒍𝒆 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆
𝟏 𝑳𝒊𝒕𝒆𝒓 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏
Small Volume → Small Amount of Solute
E. 250 mL
LARGE Volume → LARGE Amount of Solute
(Molarity)∙(Volume) = Moles of Solute
Solution Stoichiometry: Acid-Base Neutralizations
Consider the Double Replacement reaction of HNO3 with KOH:
HNO3(aq) + KOH(aq) → KNO3(aq) + HOH(l)
0.0592 MOLES
0.359 M
Volume = ?
What volume (in mL) of nitric
acid solution would be needed to
react with 0.0592 moles of KOH?
Assume the concentration of
nitric acid is 0.359 M (moles/L).
iClicker Participation Question
Acid-Base Titrations and Electrical Conductivity
For the titration of sulfuric acid with barium hydroxide, which
plot would best represent the change in conductivity versus
volume of barium hydroxide added?
H2SO4(aq) + Ba(OH)2(aq) → 2 H2O(l) + BaSO4(s)
A.
Volume of Ba(OH)2
B.
Volume of Ba(OH)2
C.
Volume of Ba(OH)2
D. The conductivity would NOT change
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Double Replacements:
Redox Reactions:
Combustions
Single Replacements
Decompositions
Types of Reactions
Reactions can be grouped
into general categories.
Each category follows a
pattern that can be used
to predict the possible
products & outcomes of
the chemical reaction in
question.
Synthesis
SINGLE Replacement Reactions
Single Replacement: a reaction where one type of element is
replaced with another.
This most often occurs when an ionic compound reacts with
a substance composed of a single element.
Single replacement reactions are a type of of REDOX
reaction (involving an exchange of electrons)
Batteries make use of Redox reactions: Write the balanced equation
for Zinc metal reacting with copper (II) sulfate to produce zinc (II) sulfate
and copper metal.
SINGLE Replacement Reactions
Magnesium metal can burn with carbon dioxide in a single
replacement reaction. Write the balanced equation for this
reaction.
If 30 g of Mg was mixed with 30 g of carbon dioxide, what is the
theoretical yield of MgO? What is the theoretical yield of
carbon?
FIRST: calculate the limiting reagent by finding the
maximum amount of product (MgO) that could form IF each
reactant was fully consumed.
THEN: compare the amount of product that could form in
each case. The reactant that produces less product is the
limiting reagent & LIMITS the formation of product.
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Galvanized Steel
Iron metal corrodes in the presences of oxygen and water to produce rust
(Fe2O3), which compromises the strength of the metal. Galvanized steel
uses a barrier of zinc or magnesium metal to protect the iron from
corrosion.
Write the balanced equation for magnesium
metal reacting with Iron (III) Oxide (aka “rust”)
to produce Iron metal & magnesium oxide.
In the course of history, the discovery of single reactions has repeatedly
revolutionized human civilizations. The start of the Iron Age around 1300 B.C.
marked the moment we learned to transform brittle iron ores to iron metal.
This affected everything from how we grew food to how we waged wars.
Write the balanced chemical equation describing
iron (III) oxide reacting with carbon atoms to form
iron metal and carbon dioxide.
• How much iron metal could be produced from 100.0 grams of Fe2O3
& 30. grams of Carbon? What if only 10.3 grams of iron metal were
obtained? What would be the percent yield?
Combustions: Reactions with Oxygen (O2)

Combustion often occurs with hydrocarbons (CxHy) to produce
CO2 & H2O:
Balance Carbon first, Hydrogen second, and Oxygen last.

Other substances can also combust (“burn”) in oxygen.
◦ Write the combustion of Iron metal to product Iron (III) Oxide (aka “rust”)
◦ Write the combustion of Phosphorus (as P4) to form P4O10
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iClicker Participation Question:
Combustion of Gasoline
How many oxygen molecules (O2) are needed to
completely react with one molecule of C7H16
(a component of gasoline) to form
A. 7
carbon dioxide and water?
B. 8
C. 11
D. 14
E. 22
Decomposition: From One to Many

A single substance breaks into multiple simpler substances
◦ Some decompositions are SPONTANEOUS.
 Example: Hydrogen peroxide decomposes to oxygen gas and water
 Example: Carbonic acid (H2CO3) decomposes
to carbon dioxide gas & water
◦ Others decompositions require heat, light
or electrical current to occur.
 Example: Water can be forced to break into its
component elements through electrolysis
(decomposition from electricity)
Thermal Decomposition:
Breaking a substance down with thermal energy
Write the balanced equation for the decomposition of mercury (II)
oxide to produce mercury metal & oxygen gas
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SYNTHESIS
Simple substances combine to form more complex compounds.
Example: Tungesten (IV) carbide can be made by heating Tungsten
metal with Carbon to 1400 oC. Write the balanced chemical equation for
this process.
Example: Write the balanced equation for forming Chlorine Trifluoride
from Chlorine & Fluorine gas.
In an industrial accident, a spill of 900 kg of chlorine trifluoride BURNED
through 12 inches of concrete & almost 3 feet of gravel beneath!
How many grams of oxygen would be needed to fully burn
1.00 gram of Magnesium metal?
Molar Masses (g/mol):
2 Mg + O2
24.31 32.00
2 MgO
40.31
Remember: the stoichiometric coefficients are only
used to relate one substance to another. They are NOT
used to calculate mole quantities.
Consider the reaction of 20.0 mL of a sulfuric acid solution
with a 0.127 M solution of sodium hydroxide:
H2SO4(aq) + 2 NaOH(aq) → Na2SO4(aq) + 2 HOH(l)
20.0 mL
Concentration = ?
32.66 mL
0.127 M
If 32.66 mL of NaOH is required to
fully react with the H2SO4 solution,
what is the concentration (in mol/L) of
the original H2SO4 solution?
Concentration =
𝒎𝒐𝒍𝒆𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆
𝒗𝒐𝒍𝒖𝒎𝒆 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 (𝑳)
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The Limiting Reagent is used to
calculate the Theoretical Yield.
If 30 g of Mg was mixed with 30 g of carbon dioxide, what is the
maximum amount of magnesium oxide that could form? In
other words, calculate the theoretical yield.
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