CHM 2046C Module Eleven-Chapter 14 Name:____________

 

Module Eleven: Acid/Base Equilibria McMurry Chapter 14

Possible

Actual

A. Idenification of Bronsted-Lowry/Lewis acids&bases

5

 

B. Writing Equilibrium Constant Expressions

5

 

C. Determination of Kw from Kc ; Kb from Ka & Kw ; Show Kb x Ka = Kw Lecture

5

 

D. Determination of pH & pOH from concentrations Problems

5

 

E. Determination of pH of weak acids/bases Problems

5

 

F. Hydrolysis Reactions 

5

 

G. Common Ion Effect Problem

5

 

H. Discussion Questions Chapter 14

5

 

I. Determination of pH of polyprotic acids and/or Buffer Calculation Problem

5

 

J. Acid-Base Properties of Salts

5

 

Total: 50

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 C5H5N + H3O+1

 

 

 

Ka =

 

 

b. NH3 + H2O NH4 1+ + OH 1-

 

 

 

Kb =

 

 

c.                   H2CO3 + H2O = HCO3 1- + H3O+1

 

 

 

Ka =

 

 

 

d. HCO3 1- + H2O == CO3 2- + H3O+1

 

 

 

Ka2 =

 

 

 

 

 

e. C5H5N + H2O ==== + OH 1- + C5H5N+1

 

 

Kb =

 

 

 

f. H2O + H2O == 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 H3O+1 + CH3CH2 CH2CO2-1(aq)

 

 

CH3CH2 CH2CO2H

H3O+1

CH3CH2 CH2CO2-1

Initial

 

 

 

Change

 

 

 

Equilibrium

 

 

 

 

 

 

 

 

 

 

 

 

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:

 

 

 

CH3CO2H

H3O+1

CH3CO2-1

Initial

 

 

 

Change

 

 

 

Equilibrium

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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:

 

 

 

 

 

 

 

 

 

ClO 1-

OH+1

HClO

Initial

 

 

 

Change

 

 

 

Equilibrium

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(d) What is the equilibrium concentration of the sulfite ion, SO3 2- in the 0.45 M solution of H2SO3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

 

 

 

 

 

 

_____2. KNO3(s) + HOH

 

 

 

 

 

 

_____3. NH4NO3(s) + HOH

 

 

 

 

 

 

_____4. KC2H3O2 (s) + HOH

 

 

 

 

 

 

_____ 5. NH4C2H3O2 (s) + HOH

 

 

 

 

Reference: Section 14.14

Answers: http://www.fccj.us/chm2046/SampleTest/46M11iAnswer.htm