CHM 2046C Module Eleven-Chapter 14 Name:____________
Module
Eleven: Acid/Base Equilibria McMurry Chapter
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C. Determination of Kw from Kc ; Kb from Ka & Kw ; Show Kb x Ka = Kw Lecture |
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D. Determination of pH
& pOH from concentrations Problems
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H. Discussion Questions Chapter 14 |
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I. Determination of pH of polyprotic acids
and/or Buffer Calculation Problem |
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Total:
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Part A: Identification of Acids and Bases 10 points
Label the acid and the base and their corresponding conjugate pairs for the following reactions:
(1) NH4 + + Cl 1- <=====> NH3 + HCl
(2) CH3OH + Cl1- <======> HCl + CH3O1-
(3) C5H5NH+1 + H2O <=======> C5H5N + H3O+1
(4) HSeO4 1- + NH3 <=======> NH4 1+ + SeO4 2-
(5) HCO3 1- + OH 1- <==========> CO3 2- + H2O
Reference: McMurry Section
14.1
Answers: http://www.fccj.us/chm2046/SampleTest/46M11abAnswer.htm
CHM 2046C Module 11 Homework Packet
Part B: Equilibrium Constant Expressions of Acids and Bases 5 points
Write the appropriate equilibrium constant expressions for the following reactions they represent:
a. C5H5NH+1 + H2O çè C5H5N + H3O+1
Ka =
b. NH3 + H2O çè NH4 1+ + OH 1-
Kb =
c. H2CO3 + H2O ç=è HCO3 1- + H3O+1
Ka =
d. HCO3 1- + H2O ç==è CO3 2- + H3O+1
Ka2 =
e. C5H5N + H2O ç====è + OH 1- + C5H5N+1
Kb =
f. H2O +
H2O ç==è H3O 1+ +
OH 1-
Kw =
Reference: Lecture Answers: See
Part A
CHM 2046C Module 11 Chapter 14 Homework Packet
Part C: Derivation of Kw Kh Kb and Ka Chapter 14 5 points
Write the ionization reaction of water, then develop the special K for water: Kw from the Kc
Write the hydrolysis reaction for Sodium acetate, NaC2H3O2 , when it is dissolved in water. Write the Kb expression for this reaction:
Write the ionization equilibrium expression for the Ka of acetic acid: HC2H3O2 and the Kw expression for water.
Derive the Kb expression from the Ka and the Kw expressions.
There is the following connection:
Ka x Kb = Kw
Using the ionization reaction of HCN in water, demonstrate
the development of the above formula from the Ka of HCN and its
conjugate base Kb of CN-
Reference: Section 14.3 McMurry
Answers: http://www.fccj.us/chm2046/SampleTest/46M11cAnswer.htm
CHM 2046C Module 11 Homework
Packet
Part D: pH Scale Calculations 5 points
What is the pH and
pOH of the following solutions:
(1) 0.000675 M HCl
(2) 0.0025 M Ca(OH)2
(3) The pH of a cup of coffee is 4.32, calculate
the [H3O+1
]:
(4) A detergent solution
has a pH of 11.45. What is the [OH 1- ]?
Reference: Section 14.5
Answers: http://www.fccj.us/chm2046/SampleTest/46M11dAnswer.htm
CHM 2046C Module 11 –
Chapter 14 Homework Packer
Part E: Equilibria of Acids and Bases Calculations 5 points
Write the appropriate equilibrium constant expression for the following reaction::
E-1 (Determine Ka from Eq Concentrations_: A solution prepared from 0.055 mol of butanoic acid dissolved in sufficient water to give 1.0 L of solution has a pH of 2.72. Determine Ka for butanoic acid. The acid ionizes at according to the balanced equation.
CH3CH2CH2CO2H(aq) + H2O ó H3O+1 + CH3CH2
CH2CO2-1(aq)
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CH3CH2 CH2CO2H |
H3O+1 |
CH3CH2 CH2CO2-1 |
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Equilibrium |
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Reference: Section 14.8
E-2: Calaulate Eq Concentrations from Ka and in8itial concentrations: What are the equilibrium concentrations of acetic acid, the acetate ion, and hydronium ion for a 0.10 M solution of acetic acid (Ka = 1.8 x 10-5)? What is the pH of the solution?
Ionization Reaction(you write):
Write the equilibrium Reactions:
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CH3CO2H |
H3O+1 |
CH3CO2-1 |
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Change |
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Equilibrium |
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Reference: Section 14.9
(Acids) 14.12 (Bases)
Answers: http://www.fccj.us/chm2046/SampleTest/46M11efAnswer.htm
Part F: Hydrolysis Calculations 5 points
What is the pH of the bleach solution which is 5.25% by weight Sodium hypochlorite, NaClO?
The Ka of Hypochlorous acid is 3.5 x 10-8
Write Hydrolysis reactions:
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ClO 1- |
OH+1 |
HClO |
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Change |
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Equilibrium |
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Reference: Section 14.14
Answers on Part E web Page:
http://www.fccj.us/chm2046/SampleTest/46M11efAnswer.htm
CHM 2046C Module 11
Homework Packet
Part G: Common Ion Solution Calculations 5 points
A solution is prepared that is 1.50M HCOOH formic acid and 2.0 M Sodium formate. The Ka for formic acids is: 1.8 x 10-4
HCOOH + HOH <=====> H3O 1+ (aq) + HCOO 1- (aq)
HCOONa + HOH <=====> Na 1+ (aq) + HCOO 1- (aq)
What is the pH of the formic acid before adding the Sodium formate?
What is the pH of Sodium format solution before mixing?
What is the pH of the solution of formic acid and the sodium formate if in each case the volumes of the separate solutions are the same as the volume of the mixture with the concentrations that are listed above.
Reference: Section 15.2
Answers: http://www.fccj.us/chm2046/SampleTest/46M11gAnswer.htm
CHM 2046C Module 11
Homework Packet
Part H: Discussion Questions Chapter 14 5 points
Explain the difference between an Arrhenius, Bronsted-Lowry, and Lewis Acid or Arrhenius, Bronsted-Lowry, and Lewis Bases?
Arrhenius Acid
Bronsted-Lowry Acid
Lewis Acid
Write equations to show how the HCO3 1- ion can act either as an acid or a base (likewise for HPO4 2- , HSO4 1- or H2PO4 1-):
HCO3 1-
HPO4 2-
H2PO4 1-
HSO4 1-
In ionization reactions of an
acid, base, or water one of the reactant molecules is water. But in the Ka,
Kb, and Kw expressions, the concentration of water is not
included in the calculation. Why?
What is the approximate molar
concentration of water at room temperature?
Why are salts from the
neutralization of a strong acid and a weak base test acidic with litmus paper
(Likewise a salt from the neutralization a weak acid and strong base test basic
with litmus paper)?
Why are salts from the
neutralization of a strong acid and a strong base test neutral (or a pH of 7.0)
with a pH meter?
Answers: http://www.fccj.us/chm2046/SampleTest/46M11hAnswer.htm
CHM 2046C Module 11 Homework Packet
Part I: pH Polyprotic acid 5 points
Sulfurous acid, H2SO3,
is a weak acid capable of providing two hydrogen ions.
Ka1 = 1.2 x 10 -2 Ka2 = 6.2 x 10 -8
(a) Show both ionization reactions,
(b)write the equilibrium expressions for both)
(c) What is the pH of a 0.45 M solution of H2SO3
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(d) What is the equilibrium concentration of the sulfite ion, SO3 2- in the 0.45 M solution of H2SO3
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Reference 14.11 and 15.9
Answers: http://www.fccj.us/chm2046/SampleTest/46M11iAnswer.htm
CHM 2046C Module 11
Homework Packet
Part J: pH of Salts 5 points
Predict whether the following salts will test
A. acidic,
B. basic,
N neutral,
Not Enough Information to Predict
when dissolved in water.
Then show the hydrolysis reaction, if any
_____1. KCN(s) + HOH à
_____2. KNO3(s) + HOH à
_____3. NH4NO3(s) + HOH à
_____4. KC2H3O2 (s) + HOH à
_____ 5. NH4C2H3O2
(s) + HOH à
Reference: Section 14.14
Answers: http://www.fccj.us/chm2046/SampleTest/46M11iAnswer.htm