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Chapter 16: Problem 21

Label each of the following as being a strong base, a weak base, or a species with negligible basicity. In each case write the formula of its conjugate acid, and indicate whether the conjugate acid is a strong acid, a weak acid, or a species with negligible acidity: \((\mathbf{a})\mathrm{CH}_{3} \mathrm{COO}^{-},(\mathbf{b}) \mathrm{HCO}_{3}^{-},(\mathbf{c}) \mathrm{O}^{2-},(\mathbf{d}) \mathrm{Cl}^{-},(\mathbf{e}) \mathrm{NH}_{3}\)

Short Answer

Expert verified
a. CH3COO- is a weak base. Its conjugate acid is CH3COOH, which is a weak acid. b. HCO3- is a weak base. Its conjugate acid is H2CO3, which is a weak acid. c. O2- is a strong base. Its conjugate acid is OH-, which is a weak acid. d. Cl- has negligible basicity. Its conjugate acid is HCl, which is a strong acid. e. NH3 is a weak base. Its conjugate acid is NH4+, which is a weak acid.

Step by step solution

01

a. CH3COO-

CH3COO- is acetate ion, which is a weak base because when it reacts with water, it forms a weak acid (acetic acid, CH3COOH) and hydroxide ion (OH-). Its conjugate acid is CH3COOH, which is a weak acid.
02

b. HCO3-

HCO3- is bicarbonate ion, which is a weak base as well because it forms H2CO3 (carbonic acid) and OH- when it reacts with water. Its conjugate acid is H2CO3, which is also a weak acid.
03

c. O2-

O2- is oxide ion, and it is a strong base because when it reacts with water, it forms hydroxide ions (OH-) and water. Its conjugate acid is OH-, which is a weak acid.
04

d. Cl-

Cl- is chloride ion, and it has negligible basicity because it forms a very weak base (HCl, which is a strong acid) when it reacts with water. Hence, there is no significant reaction of Cl- with water. Its conjugate acid is HCl, which is a strong acid.
05

e. NH3

NH3 is ammonia, which is a weak base because it forms NH4+ (ammonium ion) and OH- when it reacts with water. Its conjugate acid is NH4+, which is a weak acid.

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Most popular questions from this chapter

Predict the products of the following acid-base reactions, and predict whether the equilibrium lies to the left or to the right of the reaction arrow: (a) \(\mathrm{NH}_{4}^{+}(a q)+\mathrm{OH}^{-}(a q) \rightleftharpoons\) (b) \(\mathrm{CH}_{3} \mathrm{COO}^{-}(a q)+\mathrm{H}_{3} \mathrm{O}^{+}(a q)\) (c) \(\mathrm{HCO}_{3}^{-}(a q)+\mathrm{F}(a q) \rightleftharpoons\)

Phenylacetic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{COOH}\right)\) is one of the substances that accumulates in the blood of people with phenylketonuria, an inherited disorder that can cause mental retardation or even death. A 0.085\(M\) solution of \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{COOH}\) has a pH of \(2.68 .\) Calculate the \(K_{a}\) value for this acid.

Addition of phenolphthalein to an unknown colorless solution does not cause a color change. The addition of bromthymol blue to the same solution leads to a yellow color. (a) Is the solution acidic, neutral, or basic? (b) Which of the following can you establish about the solution: (i) A minimum pH, (ii) A maximum pH, or (iii) A specific range of pH values? (c) What other indicator or indicators would you want to use to determine the pH of the solution more precisely?

In many reactions, the addition of \(\mathrm{AlCl}_{3}\) produces the same effect as the addition of \(\mathrm{H}^{+} .\) (a) Draw a Lewis structure for \(\mathrm{AlCl}_{3}\) in which no atoms carry formal charges, and determine its structure using the VSEPR method. (b) What characteristic is notable about the structure in part (a) that helps us understand the acidic character of AlCl \(_{3} ?\) (c) Predict the result of the reaction between \(\mathrm{AlCl}_{3}\) and \(\mathrm{NH}_{3}\) in a solvent that does not participate as a reactant. (d) Which acid-base theory is most suitable for discussing the similarities between \(\mathrm{AlCl}_{3}\) and \(\mathrm{H}^{+}\) ?

Which, if any, of the following statements are true? (a) The stronger the base, the smaller the \(\mathrm{pK}_{b}\). (b) The stronger the base, the larger the \(\mathrm{pK}_{b}.\) (c) The stronger the base, the smaller the \(K_{b}\) . (a) The stronger the base, the larger the \(K_{b} .\) (e) The stronger the base, the smaller the \(\mathrm{p} K_{a}\) of its conjugate acid. (f) The stronger the base, the larger the \(\mathrm{p} K_{a}\) of its conjugate acid.
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