
Concept explainers
(a)
Interpretation: The pH of 0.12 M solution of KNO2 needs to be determined.
Concept Introduction: A base is the substance that gives OH- ions in its aqueous solution. On the basis of base dissociation, they can be classified as strong and weak base. On the contrary, a weak base ionized partially and reaches to equilibrium.
BOH(aq)⇌OH-(aq)+B-(aq)
An acid is the substance that gives H+ ions in its aqueous solution. On the basis of acid dissociation, acids can be classified as strong and weak acid. On the contrary, a weak acid ionized partially and reaches to equilibrium.
HA(aq)+ H2O(l)⇌H3O+(aq)+ A-(aq)
(a)

Answer to Problem 109E
pH = 8.24
Explanation of Solution
[ KNO2 ] = 0.12 M
KNO2 is a basic salt. The ionization of KNO2 forms respective ions:
KNO2→K++NO2-
Here NO2- can act as string conjugate base of weak acid HNO2 therefore the salt is slightly basic in nature as K+ is neither acidic nor basic.
The reaction of NO2- ions with water can be written as:
NO2-(aq)+ H2O(l)⇌HNO2(aq)+ OH-(aq)
Initial concentration of NO2- = 0.12 M
Kb for NO2- = 2.5× 10-11
Make ICE table:
Concentration | NO2- | OH- | HNO2 |
Initial | 0.12 | 0 | 0 |
Change | -x | x | x |
Equilibrium | 0.12−x | x | x |
Calculate H3O+ :
NO2-(aq)+ H2O(l)⇌HNO2(aq)+ OH-(aq)Kb=[OH-][HNO2][NO2-]2.5× 10-11 = [x] [x][0.12-x](0.12>>x)2.5× 10-11 = [x] [x][0.12][x]2 =2.5× 10-11 ×0.12[x]= 1.73×10-6 =[OH−]
Calculate pOH and pH:
pOH = -log[OH−] pOH = -log[1.73×10-6 ]pOH = 5.76pH = 14 - pOH = 14- 5.76 = 8.24
(b)
Interpretation: The pH of 0.45 M solution of NaOCl needs to be determined.
Concept Introduction: A base is the substance that gives OH- ions in its aqueous solution. On the basis of base dissociation, they can be classified as strong and weak base. On the contrary, a weak base ionized partially and reaches to equilibrium.
BOH(aq)⇌OH-(aq)+B-(aq)
An acid is the substance that gives H+ ions in its aqueous solution. On the basis of acid dissociation, acids can be classified as strong and weak acid. On the contrary, a weak acid ionized partially and reaches to equilibrium.
HA(aq)+ H2O(l)⇌H3O+(aq)+ A-(aq)
(b)

Answer to Problem 109E
pH = 10.5
Explanation of Solution
[ NaOCl ] = 0.45 M
NaOCl is a basic salt. The ionization of NaOCl forms respective ions:
NaOCl→Na++OCl-
Here OCl- can act as strong conjugate base of weak acid HClO therefore the salt is slightly basic in nature as Na+ is neither acidic nor basic.
The reaction of OCl- ions with water can be written as:
OCl-(aq)+ H2O(l)⇌HClO(aq)+ OH-(aq)
Initial concentration of OCl- = 0.45 M
Kb for OCl- = 2.8× 10-7
Make ICE table:
Concentration | OCl- | OH- | HClO |
Initial | 0.45 | 0 | 0 |
Change | -x | x | x |
Equilibrium | 0.45−x | x | x |
Calculate H3O+ :
OCl-(aq)+ H2O(l)⇌HClO(aq)+ OH-(aq)Kb=[OH-][HClO][OCl-]2.8× 10-7 = [x] [x][0.45-x](0.45>>x)2.8× 10-7 = [x] [x][0.45][x]2 =2.8× 10-7 ×0.45[x]= 3.55×10-4 =[OH−]
Calculate pOH and pH:
pOH = -log[OH−] pOH = -log[3.55×10-4 ]pOH = 3.45pH = 14 - pOH = 14- 3.45 = 10.5
(c)
Interpretation: The pH of 0.40 M solution of NH4ClO4 needs to be determined.
Concept Introduction: A base is the substance that gives OH- ions in its aqueous solution. On the basis of base dissociation, they can be classified as strong and weak base. On the contrary, a weak base ionized partially and reaches to equilibrium.
BOH(aq)⇌OH-(aq)+B-(aq)
An acid is the substance that gives H+ ions in its aqueous solution. On the basis of acid dissociation, acids can be classified as strong and weak acid. On the contrary, a weak acid ionized partially and reaches to equilibrium.
HA(aq)+ H2O(l)⇌H3O+(aq)+ A-(aq)
(c)

Answer to Problem 109E
pH = 4.8
Explanation of Solution
[ NH4ClO4 ] = 0.40 M
NH4ClO4 is aacidic salt. The ionization of NH4ClO4 forms respective ions:
NH4ClO4→NH4++ClO4-
Here ClO4- can act as weak conjugate base of strong acid HClO4 therefore the salt is slightly acidic in nature as NH4+ is strong conjugate acid of weak base NH3.
The reaction of NH4+ ions with water can be written as:
NH4+(aq)+ H2O(l)⇌NH3(aq)+ H3O+(aq)
Initial concentration of OCl- = 0.40 M
Ka for NH4+ = 5.6× 10-10
Make ICE table:
Concentration | NH4+ | NH3 | H3O+ |
Initial | 0.40 | 0 | 0 |
Change | -x | x | x |
Equilibrium | 0.40−x | x | x |
Calculate H3O+ :
NH4+(aq)+ H2O(l)⇌NH3(aq)+ H3O+(aq)Ka=[NH3][H3O+][NH4+]5.6× 10-10 = [x] [x][0.40-x](0.40>>x)5.6× 10-10 = [x] [x][0.40][x]2 =5.6× 10-10×0.40[x]= 1.49×10-5 =[H3O+]
Calculate pH:
pH = -log[H3O+] pH = -log[1.49×10-5]pH = 4.8
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Chapter 7 Solutions
Chemical Principles
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