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Chapter 4: Problem 27

Benzoic acid, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\left(\mathrm{p} K_{\mathrm{a}} 4.19\right)\), is only slightly soluble in water, but its sodium salt, \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COO}^{-} \mathrm{Na}^{+}\), is quite soluble in water. In which solution(s) will benzoic acid dissolve? (a) Aqueous \(\mathrm{NaOH}\) (b) Aqueous \(\mathrm{NaHCO}_{3}\) (c) Aqueous \(\mathrm{Na}_{2} \mathrm{CO}_{3}\)

Short Answer

Expert verified
Answer: Benzoic acid will dissolve in aqueous NaOH, NaHCO3, and Na2CO3 solutions.

Step by step solution

01

Reaction between benzoic acid and NaOH

NaOH is a strong base, and its pKa value is much higher than that of benzoic acid (4.19). The reaction between benzoic acid (C6H5COOH) and NaOH will produce a soluble salt (C6H5COO⁻ Na⁺). C6H5COOH + NaOH → C6H5COO⁻ Na⁺ + H2O Since NaOH has a much higher pKa value than benzoic acid, benzoic acid will dissolve in the NaOH solution.
02

Reaction between benzoic acid and NaHCO3

NaHCO3 is a weak base, and its pKa value is 10.33. However, since this is still significantly higher than the pKa of benzoic acid (4.19), a reaction will occur, and the soluble salt will form: C6H5COOH + NaHCO3 → C6H5COO⁻ Na⁺ + H2CO3 Therefore, benzoic acid will dissolve in NaHCO3 solution.
03

Reaction between benzoic acid and Na2CO3

Na2CO3 is a weak base, with a first pKa value of 6.35 and a second pKa value of 10.33. Since its first pKa value is higher than benzoic acid's pKa value (4.19), a reaction will occur, and a soluble salt will form: C6H5COOH + Na2CO3 → C6H5COO⁻ Na⁺ + NaHCO3 Therefore, benzoic acid will dissolve in Na2CO3 solution. In conclusion, benzoic acid will dissolve in all three solutions, as each base reacts with benzoic acid to form a soluble salt (C6H5COO⁻ Na⁺), and the solution's pKa value is greater than that of benzoic acid.

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Most popular questions from this chapter

Each molecule or ion can function as a base. Write a structural formula of the conjugate acid formed by reaction of each with \(\mathrm{HCl}\). (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}\) (b) \(\mathrm{HCH}\) (c) \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{NH}\) (d) \(\mathrm{HCO}_{3}{ }^{-}\)

Write an equation for the reaction between each Lewis acid-base pair, showing electron flow by means of curved arrows. (a) \(\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{3} \mathrm{~B}+\mathrm{OH}^{-} \longrightarrow\) (b) \(\mathrm{CH}_{3} \mathrm{Cl}+\mathrm{AlCl}_{3} \longrightarrow\)

Offer an explanation for the following observations. (a) \(\mathrm{H}_{3} \mathrm{O}^{+}\)is a stronger acid than \(\mathrm{NH}_{4}^{+}\). (b) Nitric acid, \(\mathrm{HNO}_{3}\), is a stronger acid than nitrous acid, \(\mathrm{HNO}_{2}\). (c) Ethanol and water have approximately the same acidity. (d) Trifluoroacetic acid, \(\mathrm{CF}_{3} \mathrm{COOH}\), is a stronger acid than trichloroacetic acid, \(\mathrm{CCl}_{g} \mathrm{COOH}\).

Following is a structural formula for the tert-butyl cation. (We discuss the formation, stability, and reactions of cations such as this one in Chapter 6 .) C[C+](C)C tert-Butyl cation (a carbocation) (a) Predict all \(\mathrm{C}-\mathrm{C}-\mathrm{C}\) bond angles in this cation. (b) What is the hybridization of the carbon bearing the positive charge? (c) Write a balanced equation to show its reaction as a Lewis acid with water. (d) Write a balanced equation to show its reaction as a Brønsted-Lowry acid with water.

In acetic acid, \(\mathrm{CH}_{3} \mathrm{COOH}\), the \(\mathrm{OH}\) hydrogen is more acidic than the \(\mathrm{CH}_{3}\) hydrogens. Explain.
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