Introduction to General, Organic and Biochemistry
Introduction to General, Organic and Biochemistry
11th Edition
ISBN: 9781285869759
Author: Frederick A. Bettelheim, William H. Brown, Mary K. Campbell, Shawn O. Farrell, Omar Torres
Publisher: Cengage Learning
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Chapter 8, Problem 8.91P
Interpretation Introduction

Interpretation:

Why the setup for Kb values for bases and in a similar manner the Ka values for acids is considered unnecessary should be explained.

Concept Introduction:

There are associated scales within the chemistry utilized to find out how basic and acidic a solution is, as well as the strength of bases and acids. Though most familiar is pH scale, Ka, pKa, Kb and pKb are the common calculation which offer understanding into acid-base reactions.

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Answer to Problem 8.91P

Scale of Kb values for bases is unnecessary because the strength of two bases can be compared from the strength of their conjugate acids.

Explanation of Solution

The acid ionization constant, Ka, is the equilibrium constant for acid’s ionization. For the ionization of an acid, say HA, in an aqueous solution we get.

HA + H2 H3O+ + A-Ka = [H3O+][A][HA]

The square brackets denote the concentration. The concentration of water is not considered as water is exist in excess.

The Ka equation displays that the greater the dissociation of acid, the greater the value of Ka.

If there is a stringer acid, it will dissociate to a greater extent. Therefore, the numerator within the equation of Ka is larger, and thus, Ka will have the greater value.

Therefore, the weak acid’s strength is expressed in terms of Ka.

As per the Bronsted-Lowry concept of bases and acids, an acid is known as the proton donor, and a base is the proton acceptor.

When an acid donates a proton to another ion or molecule, it is converted to the conjugate base. For illustration,

CH3COOH(aq) + H2O(l CH3COO(aq) + H3O+(aq)Acetic acid                                 Acetate ion       Hydronium ion   (acid)                                      (Conjugate base                                                     of acid) 

When a base accepts a proton, it is converted to the conjugate acid. For illustration.

NH3(aq) + H2O(l)     NH4+(aq)      +    OH(aq)Ammonia    water        Ammomium ion      Hydroxide ion   (base)                        (Conjugate acid                                        of base) 

As per the Bronsted-Lowry definitions any molecules or ions pairs which might be interconverted by the transfer of proton is known as conjugate acid-base pair. Therefore, CH3 COOH and CH3 COO- is a conjugate acid-base pair and NH3 andNH4 + is a conjugate acid-base pair.

There is an inverse relationship amid the strength of acid and its conjugate base. The stronger the acid, the weaker is the conjugate base. The acid ionization constant, Ka, expresses the weak acid’s strength.

The below table shows values of ka for weak acids:

Ka values of weak acids.

Formula Name Ka
H3 PO4 Phosphoric acid 7.5×103
HCOOH Formic acid 1.8×104
CH3 CH(OH)COOH Lactic acid 1.4×104
CH3 COOH Acetic acid 1.8×105
H2 CO3 Carbonic acid 4.3×107
H2 PO4 - Dihydrogen phosphate ion 6.2×108
H3 BO3 Boric acid 7.3×1010
NH4 + Ammonium ion 5.6×1010
HCN Hydrocyanic acid 4.9×1010
C6 H5 OH Phenol 1.3×1010
HCO3 - Bicarbonate ion 5.6×1011
HPO42 - Hydrogen phosphate ion 2.2×1013

If we want to compare the strength of two bases, we can compare the strength of their conjugate acids.

For illustration, let us compare the strength of two bases, phenoxide ion C6 H5 O- and bicarbonate ion HCO3-.

The conjugate acid of phenoxide ion i.e. C6 H5 O- is phenol C6 H5 OH.

Ka of phenol = 1.3×1010

The conjugate acid of bicarbonate ion HCO3 - is carbonic acid H2 CO3.

Ka of carbonic acid = 4.3×107

Therefore, Ka of the carbonic acid is greater than Ka of phenol. Hence, the carbonic acid is stronger than phenol. The stronger the acid, the weaker is the conjugate base. Therefore, a phenoxide ion is stronger base than a bicarbonate ion.

Therefore, we could compare the strength of weak bases from the Ka scale of acids. Hence, a scale of Kb values for bases is unncessary.

Conclusion

Since, the strength of two bases can be compared from the strength of their conjugate acids thus, scale of Kb values for bases is unnecessary.

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Chapter 8 Solutions

Introduction to General, Organic and Biochemistry

Ch. 8.11 - Problem 8-11 What is the pH of a boric acid buffer...Ch. 8.12 - Prob. 8.12PCh. 8 - 8-13 Define (a) an Arrhenius acid and (b) an...Ch. 8 - 8-14 Write an equation for the reaction that takes...Ch. 8 - 8-15 Write an equation for the reaction that takes...Ch. 8 - 8-16 For each of the following, tell whether the...Ch. 8 - 8-17 For each of the following, tell whether the...Ch. 8 - 8-18 Which of these acids are monoprotic, which...Ch. 8 - 8-19 Define (a) a Brønsted—Lowry acid and (b) a...Ch. 8 - 8-20 Write the formula for the conjugate base of...Ch. 8 - 8-21 Write the formula for the conjugate base of...Ch. 8 - Prob. 8.22PCh. 8 - Prob. 8.23PCh. 8 - Prob. 8.24PCh. 8 - 8-25 Draw the acid and base reactions for the...Ch. 8 - Prob. 8.26PCh. 8 - Prob. 8.27PCh. 8 - 8-28 Will carbon dioxide be evolved as a gas when...Ch. 8 - Prob. 8.29PCh. 8 - Prob. 8.30PCh. 8 - Prob. 8.31PCh. 8 - Prob. 8.32PCh. 8 - 8-33 Write an equation for the reaction of HCI...Ch. 8 - 8-34 When a solution of sodium hydroxide is added...Ch. 8 - 8-35 Given the following values of [H3O+),...Ch. 8 - 8-36 Given the following values of [OH-],...Ch. 8 - 8-37 What is the pH of each solution given the...Ch. 8 - 8-38 What is the pH and pOH of each solution given...Ch. 8 - 8-39 What is the pH of each solution given the...Ch. 8 - Prob. 8.40PCh. 8 - 8-41 What is the [OH-] and pOH of each solution?...Ch. 8 - Prob. 8.42PCh. 8 - 8-43 What is the molarity of a solution made by...Ch. 8 - 8-44 What is the molarity of a solution made by...Ch. 8 - 8-45 Describe how you would prepare each of the...Ch. 8 - 8-46 If 25.0 mL of an aqueous solution of H2SO4...Ch. 8 - 8-47 A sample of 27.0 mL of 0.310 M NaOH is...Ch. 8 - 8-48 A 0.300 M solution of H2SO4 was used to...Ch. 8 - 8-49 A solution of NaOH base was titrated with...Ch. 8 - 8-50 The usual concentration of HCO3- ions in...Ch. 8 - 8-51 What is the end point of a titration?Ch. 8 - Prob. 8.52PCh. 8 - 8-53 Write equations to show what happens when, to...Ch. 8 - 8-54 Write equations to show what happens when, to...Ch. 8 - 8-55 We commonly refer to a buffer as consisting...Ch. 8 - Prob. 8.56PCh. 8 - Prob. 8.57PCh. 8 - 8-58 What is the connection between buffer action...Ch. 8 - Prob. 8.59PCh. 8 - 8-60 How is the buffer capacity affected by the...Ch. 8 - 8-61 Can 100 of 0.1 M phosphate buffer at pH 7.2...Ch. 8 - 8-62 What is the pH of a buffer solution made by...Ch. 8 - 8-63 The pH of a solution made by dissolving 1.0...Ch. 8 - Prob. 8.64PCh. 8 - Prob. 8.65PCh. 8 - 8-66 Calculate the pH of an aqueous solution...Ch. 8 - Prob. 8.67PCh. 8 - 8-68 If you have 100 mL of a 0.1 M buffer made of...Ch. 8 - Prob. 8.69PCh. 8 - Prob. 8.70PCh. 8 - 8-71 Explain why you do not need to know the...Ch. 8 - Prob. 8.72PCh. 8 - Prob. 8.73PCh. 8 - Prob. 8.74PCh. 8 - Prob. 8.75PCh. 8 - 8-76 (Chemical Connections 8B) Name the most...Ch. 8 - Prob. 8.77PCh. 8 - Prob. 8.78PCh. 8 - 8-79 (Chemical Connections 8D) Another form of the...Ch. 8 - Prob. 8.80PCh. 8 - Prob. 8.81PCh. 8 - 8-82 Assume that you have a dilute solution of HCI...Ch. 8 - Prob. 8.83PCh. 8 - Prob. 8.84PCh. 8 - Prob. 8.85PCh. 8 - 8-86 Following are three organic acids and the...Ch. 8 - 8-87 The pKavalue of barbituric acid is 5.0. If...Ch. 8 - Prob. 8.88PCh. 8 - Prob. 8.89PCh. 8 - Prob. 8.90PCh. 8 - Prob. 8.91PCh. 8 - Prob. 8.92PCh. 8 - 8-93 Do a 1.0 M CH3COOH solution and a 1.0 M HCI...Ch. 8 - 8-94 Suppose you wish to make a buffer whose pH is...Ch. 8 - Prob. 8.95PCh. 8 - 8-96 Suppose you want to make a CH3COOH/CH3COO-...Ch. 8 - Prob. 8.97PCh. 8 - 8-98 When a solution prepared by dissolving 4.00 g...Ch. 8 - Prob. 8.99PCh. 8 - Prob. 8.100PCh. 8 - 8-101 Suppose you have an aqueous solution...Ch. 8 - Prob. 8.102PCh. 8 - 8-103 Suppose you have a phosphate buffer...Ch. 8 - Prob. 8.104PCh. 8 - Prob. 8.105PCh. 8 - Prob. 8.106PCh. 8 - 8-107 Following are pH ranges for several human...Ch. 8 - 8-108 What is the ratio of HPO42-/H2PO4- in a...Ch. 8 - Prob. 8.109PCh. 8 - 8-110 A concentrated hydrochloric acid solution...Ch. 8 - 8-111 The volume of an adult's stomach ranges from...Ch. 8 - 8-112 Consider an initial 0.040 M hypobromous acid...Ch. 8 - Prob. 8.113PCh. 8 - Prob. 8.114PCh. 8 - 8-115 When a solution prepared by dissolving 0.125...Ch. 8 - 8-116 A railroad tank car derails and spills 26...Ch. 8 - Prob. 8.117P
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