Section 6.4

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Section 6.4Solubility Precipitation
How can we make sure everything thats added to
the sports drink will dissolve?
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A Review of Double-Replacement Reactions
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Double Replacement Reactions
The cations from two compounds replace each other.
NaCl AgNO3 ? AgCl NaNO3
Two ionic compounds switch ions
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Double Replacement Reactions
General format of a double replacement reaction
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Products of a Double Replacement
Combine the cation of the first reactant with the
anion of the second reactant
1
Ca
Cl2

Ag
NO3
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Products of a Double Replacement
Combine the cation of the second reactant with
the anion of the first reactant
2
Ca
Cl2

Ag
NO3
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Products of a Double Replacement
Remember to write cations first
3
balance charges with subscripts when writing
formulas
Only leave subscripts that are in the original
compound there if they are a part of a polyatomic
ion!
Ca
Cl2

Ag
NO3


AgCl
Ca(NO3)2
Ca
Cl2
Ag
NO3
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Precipitation Reactions
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Precipitation Reactions

• A precipitation reaction is when 2 soluble
  substances are mixed together and they form an
  insoluble substance. This is called a
  precipitate.
• Reactants
• 2 soluble
• 
  chemicals
• NaOH and
  Cu(NO3)2

NaOH
Cu(NO3)2
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Precipitation Reactions(DR Rxns)
Cu2 NO3 -1
Na1 OH-1
Cu(OH)2(S)
Products 1 soluble chemical NaNO3 1 insoluble
chemical (the precipitate) Cu(OH)2
Na1 NO3 -1
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Solubility Rules
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Solubility Rules Table
Use the table on the reference sheet!
Insoluble Precipitate
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Lets Practice 1
NaNO3 Fe(C2H3O2)2 CaBr2 Ba(OH)2 Cu(OH)2
Example Decide whether each is soluble or not
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Lets Practice 1
Soluble Soluble Soluble Soluble Not Soluble
NaNO3 Fe(C2H3O2)2 CaBr2 Ba(OH)2 Cu(OH)2
Example Decide whether each is soluble or not
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Lets Practice 2
Remember to indicate compounds that dissolve with
aq for aqueous and compounds that dont
dissolve with s for solid
Example Write the products for this reaction
predict the precipitate
AgNO3 (aq) NaCl (aq) ?
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Lets Practice 2
Example Write the products for this reaction
AgNO3 (aq) NaCl (aq) ?
AgCl (s) NaNO3 (aq)
precipitate
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Lets Practice 3
Remember to indicate compounds that dissolve with
aq for aqueous and compounds that dont
dissolve with s for solid
Example Write the products for this reaction
identify the precipitate
BaCl2 (aq) K2CO3 (aq) ?
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Lets Practice 3
Example Write the products for this reaction
BaCl2 (aq) K2CO3 (aq) ?
KCl (aq) BaCO3 (s)
precipitate
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Net Ionic Reactions
Shows the details of aqueous reactions that
involve ions in aqueous solution
Molecular Equation the typical equation you are
use to writing keeping all molecules together

• Complete Ionic Equation shows all the particles
  in a solution as they really exist, as IONS or
  MOLECULES.
• Anything aqueous needs to be split apart into
  the cation and anion
• Anything solid stays intact
• Coefficients need to be multiplied by subscripts
  to determine the exact amount of each cation and
  anion.

Spectator ions ions that do not participate in a
reaction they are identical on both sides of the
equation are crossed out!
Net Ionic Equation the final equation showing
the major players. All spectator ions have been
removed.
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NET IONIC REACTIONS for Precipitation Reactions
Molecular equation KI(aq) AgNO3(aq) ?
AgI(s) KNO3(aq)
Complete Ionic equation K1 I-1 Ag1 NO3-1
? AgI K1 NO3-1
Spectator ions ions that do not participate in a
reaction they are identical on both sides of the
equation are crossed out!
Net Ionic equation
I-1 Ag1 ? AgI
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NET IONIC REACTIONS for Precipitation Reactions
Molecular equation 2 NaOH(aq)
CuCl2(aq) ? 2 NaCl(aq) Cu(OH)2(s)
Complete Ionic equation 2 Na1 2 OH-1 Cu2
2 Cl-1 ? 2 Na1 2 Cl-1 Cu(OH)2
Net Ionic equation
2 OH-1 Cu2 ? Cu(OH)2
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Take Home PracticePredict products and balance
Iron (III) chloride reacts with sodium hydroxide
Molecular equation 1 FeCl3(aq) 3
NaOH(aq) ? 1 Fe(OH)3(s) 3 NaCl(aq)
Complete Ionic equation 3 Na1 3 OH-1 Fe3
3 Cl-1 ? 3 Na1 3 Cl-1 Fe(OH)3
Net Ionic equation
3 OH-1 Fe3 ? Fe(OH)3
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Section 6.5Stoichiometry
How can we determine in a lab the concentration
of electrolytes?
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What do those coefficients really mean?
The coefficient of the balanced chemical equation
tells how many moles of each substance is used in
the reaction.
For every 2 moles of H2
and 2 moles of H2O are produced
2
2
2 H2 O2 ? 2 H2O
No coefficient 1
1 mole of O2 is need to react
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Mole Ratio
Is a conversion factor that relates 2 substances
in moles must use a balanced chemical equation
to create it
2 H2 O2 ? 2 H2O
Examples of Mole Ratios 2mol H2
1 mol O2 2 mol H2O 1 mol O2
2 mol H2O 2 mol H2
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What is stoichiometry?
Stoichiometry Calculations using the mole ratio
from the balanced equation and information about
one compound in the reaction to determine
information about another compound in the
equation.
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Example What is the mole ratio of chlorine to
sodium?
2 Na Cl2 ? 2 NaCl
2mol Na 1 mol Cl2 2 mol
Na 1 mol Cl2 2 mol NaCl 2 mol NaCl
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Stoich (Mole-Mole) 1 step problemusing the
mole ratio
Example If 4.2 mole of H2 reacts completely with
O2, how many moles of O2 are needed? 2 H2 O2 ?
2 H2O
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Stoichiometry with Moles
Example If 4.2 mole of H2 reacts completely with
O2, how many moles of O2 are needed? 2 H2 O2 ?
2 H2O
From balanced equation 2 mole H2 ? 1 mole O2
mole O2
1
4.2 mole H2
________ mole O2
2.1
mole H2
2
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Stoich (Mole-Mole)
Example If 0.67 moles of potassium nitrate
reacts, how many moles of oxygen are produced?
2KNO3 ? 2KNO2 O2
From balanced equation 2 mole KNO3 ? 1 mole O2
mole O2
1
0.67 mole KNO3
________ mole O2
0.34
Mole KNO3
2
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But we cant measure moles in lab!
We cant go to the lab and count or measure
molesso we need a way to work in measurable
units, such as grams and liters!
Molecular mass gives the grams 1 mole of a
compound!
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Stoich( Mole-Mass) 2 step problemuse mole ratio
then molar mass conversion factors
Example How many grams of AgCl will be
precipitated if 0.45 mole AgNO3 is reacted as
follows 2 AgNO3 CaCl2 ? 2 AgCl Ca(NO3)2
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Stoichiometry with Moles Mass
Example How many grams of AgCl will be
precipitated if 0.45 mole AgNO3 is reacted as
follows 2 AgNO3 CaCl2 ? 2 AgCl Ca(NO3)2
From balanced equation 2 mole AgNO3 ? 2 mole
AgCl
Molar Mass of AgCl 1 mole AgCl 143.32 g
0.45 mole AgNO3
2
g AgCl
143.32
mole AgCl
________ g AgCl
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mole AgNO3
2
mole AgCl
1
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Stoich( Mass- Mol) 2 step problemuse molar mass
then mole ratio conversion factors
Example If 4.42 g of H2 reacts, how many moles
of NH3 are produced? N2 3H2 ? 2NH3
From balanced equation 3 mole H2 ? 2 mole N2
Mole H2
1
4.42 g H2
2 mole NH3
1.46 mole NH3
g H2
2.02
3 mole H2
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Stoich( Mass-Mass) 3 step problemuse molar
mass, then mole ratio then molar mass
conversion factors (Honors Only)
Example How many grams Ba(OH)2 are precipitated
from 14.5 g of NaOH in the following reaction 2
NaOH BaCl2 ? Ba(OH)2 2 NaCl
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Stoichiometry with Mass (Honors)
Example How many grams Ba(OH)2 are precipitated
from 14.5 g of NaOH in the following reaction 2
NaOH BaCl2 ? Ba(OH)2 2 NaCl
Molar Mass of NaOH 1 mole NaCl 40.00 g
From balanced equation 2 mole NaOH ? 1 mole
Ba(OH)2
Molar Mass of Ba(OH)2 1 mole Ba(OH)2 171.35 g
14.5 g NaOH
1
mole Ba(OH)2
1
mole NaOH
g Ba(OH)2
171.35
g NaOH
40.00
mole NaOH
2
mole Ba(OH)2
1
31.1
________ g Ba(OH)2
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Stoichiometry with Mass (Honors)
Example How many grams of HCl are needed to
produce 65.0 g of magnesium chloride __Mg
____HCl ? ____MgCl2 __H2
Balance the equation and fill in the missing
information
g HCl
mole HCl
1 mole MgCl2
g HCl
65 g MgCl2
mole MgCl2
mole HCl
g MgCl2
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What about the stoichiometry of gases? Recall
Molar Volume of a Gas at STP 1
mole of any gas 22.4 liters
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Stoichiometry with Gases 1 mol 22.4 L
_at_STP
Example If you need react 1.5 g of zinc
completely, what volume of hydrogen gas will be
produced at STP? 2 HCl (aq) Zn (s) ? ZnCl2 (aq)
H2 (g)
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Stoichiometry with Gases
Example If you need react 1.5 g of zinc
completely, what volume of hydrogen gas will be
produced at STP? 2 HCl (aq) Zn (s) ? ZnCl2 (aq)
H2 (g)
Molar volume of a gas 1 mole H2 22.4 L
From balanced equation 1 mole Zn ? 1 mole H2
Molar Mass of Zn 1 mole Zn 65.39 g
1.5 g Zn
mole Zn
1
mole H2
1
L H2
22.4
g Zn
65.39
mole Zn
1
mole H2
1
0.51
________ L H2
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Stoichiometry with Gases
Example How many moles of water will be produced
from the complete combustion of 7.3 L of oxygen
gas? Assume STP C3H8 5O2 ? 3CO2 4H2O
Molar volume of a gas 1 mole O2 22.4 L
From balanced equation 4 mole H2O ? 5 mole O2
Molar Mass of H 1 mole H2O 18 g
7.3 L O2
1
mole H2 O
4
Mole O2
L O2
22.4 L
Mole O2
5
0.26 mole H2O
_
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Keeping all these equalities straight!
TO GO BETWEEN USE THE EQUALITY
Grams moles Molar mass (g) 1 mole
Particles Moles 1 mol 6.02 x 1023 particles
Moles liters of a gas at STP 1 mole 22.4 L at STP
2 different chemicals in a reaction Coefficient ratio(MOLE RATIO) from balanced equation
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You Try!

• Given the UNBALANCED EQUATION __MgCO3 ? __MgO
  __CO2, how many liters of CO2 gas are produced
  from the reaction of 15 grams of MgCO3? Assume
  STP!
•  

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Section 6.5b

• Percent Yield

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Percent Yield

• A Yield is a product
• Actual Yield(A) the actual amount of product you
  produce in the lab
• Theoretical Yield(T) the amount of product you
  should produce if nothing went wrong use the
  balanced chemical equation to calculate this
  amount.
• Percent Yield ratio of actual yield to
  theoretical yield

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Percent Yield

• yield A x 100
• T
• Lets Practice in steps
• 1a. If 4.20 moles H2 reacts completely with
  oxygen, how many grams of H2O are produced?
  
• 2 H2 O2 ? 2 H2O
• This is a mol-mass problem.
• Your answer is the theoretical yield of water?

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If 4.20 moles H2 react completely with oxygen how
many grams of H2O are produced?
2 H2 O2 ? 2 H2O
From balanced equation 2 mole H2O ? 1 mole O2
Molar Mass of O2 1 mole H2O 18.02g
18.02 grams H2O
2 moleH2O
75.7 g
4.2 mol H2
______g H2O
1 mole H2O
2 mol H2
This is the theoretical yield.
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What is the percent yield if 60.0 grams of H2O
are produced?
A 60.0 g T 75.7 g
yield A x 100 T
yield 60.0x 100 75.7 79.3 yield
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You have precipitated 8.50 g of Ba(OH)2. If you
start with 4.57 grams of NaOH, what is the
yield. 2 NaOH BaCl2 ? Ba(OH)2
2 NaCl
From balanced equation 2 mole NaOH ? 1 mole
Ba(OH)2
Molar Mass of Ba(OH)2 173.25 g
Molar Mass of NaOH 40.00 g
171.35g Ba(OH)2
1 molBa(OH)2
1 molNaOH
4.57 g NaOH
40.00g NaOH
2 mol NaOH
1mol Ba(OH)2
9.79 g Ba(OH)2
This is the theoretical yield.
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If 9.78 grams are obtained in the experiment,
what is the percent yield?
A 8.50 g T 9.79 g
yield A x 100 T
yield 8.50 x 100 9.79
86.8 yield
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Section 6.5c

• Titrations

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TitrationsUsing Stoichiometry

• Titration A technique where the addition of a
  known volume of a known concentration solution to
  a known volume of unknown concentration solution
  to determine the concentration.
• Use a buret to titrate unknown concentration of
  solutions.

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TitrationsUsing Stoichiometry
The titrant is the known concentration in the
buret and the analyte is the unknown
concentration in the flask. Formula nMaVa
nMbVb na number of H in the acid nb number
of OH- in the base Ma molarity of acid Mb
molarity of base V volume
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End Point vs. Equivalence Point

• Equivalence Point (or Stoichiometric Point)
• When there are no reactants left overthey have
  all been reacted and the solution contains only
  products
• the point where the acid and the base are equal
  in equal moles
• moles acid moles base

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Importance of Indicators

• Indicators Paper or liquid that change color
  based on pH level.
• End Point point at which the indicator in the
  solution changes color
• It signals the equivalence point and the stop of
  the titration

• Always select an indicator that has a pH value
  close to that of the pH of the equivalence point
  of the titration.

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Titration Process
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Titration Problem 1

• How many liters of 0.10 M NaOH is needed to react
  with 0.125 L of 0.25 M HCl?
• NaOH HCl ? H2O NaCl

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Titration Problem 2

• What is the molarity of a Ca(OH)2 solution if
  30.0 ml of the solution is neutralized by 20.0 ml
  of a 0.50 M solution of HCl?
•   Ca(OH) 2 2HCl ? 2H2O CaCl2

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Titration Problem 3

• What volume of 2.0M solution of NH4OH is needed
  to neutralize 50.0 ml of a 0.50M solution of
  H2SO4?
• 2 NH4OH H2SO4 ? 2H2O (NH4) 2SO4

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Titration Curves
Strong Base - Strong Acid
Weak Base - Strong Acid

• Shows the changes of pH during a titration
• Identifies the pH of the equivalence point

Weak Base - Weak Acid
Strong Base - Weak Acid
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Titration curve for Titrating a strong acid with
a strong base pH is always 7
The titration curve graph shows the pH of the
equivalence point. Take the vertical region and
cut the length in half and then look to what pH
value aligns to that point.
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Titration curve for Titrating a strong base with
an strong acid pH is always 7
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Titration curve for Titrating a weak acid with
an strong base pH is gt7