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Chapter 4: Problem 28

4-Methylphenol, \(\mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{OH}\left(\mathrm{p} K_{\mathrm{a}} 10.26\right.\) ), is only slightly soluble in water, but its sodium salt, \(\mathrm{CH}_{3} \mathrm{C}_{6} \mathrm{H}_{4} \mathrm{O}^{-} \mathrm{Na}^{+}\), is quite soluble in water. In which solution(s) will 4-methylphenol dissolve? (a) Aqueous \(\mathrm{NaOH}\) (b) Aqueous \(\mathrm{NaHCO}_{3}\) (c) Aqueous \(\mathrm{Na}_{2} \mathrm{CO}_{3}\)

Short Answer

Expert verified
(b) Aqueous NaHCO3 So, 4-methylphenol will dissolve in aqueous NaOH and aqueous NaHCO3 solutions.

Step by step solution

01

Identify the conjugate acids of the anions in the solutions

We will first list the conjugate acids of the anions in the given solutions and their pKa values. - In aqueous NaOH, the anion is \(\mathrm{OH}^{-}\), and its conjugate acid is water (\(\mathrm{H}_{2}\mathrm{O}\)) with a pKa value of 15.7. - In aqueous NaHCO3, the anion is \(\mathrm{HCO}_{3}^{-}\), and its conjugate acid is carbonic acid (\(\mathrm{H}_{2}\mathrm{CO}_{3}\)) with a pKa value of 6.35 for the first dissociation. - In aqueous Na2CO3, the anion is \(\mathrm{CO}_{3}^{2-}\), and its conjugate acid is bicarbonate (\(\mathrm{HCO}_{3}^{-}\)) with a pKa value of 10.33 for the second dissociation.
02

Compare the pKa values of the conjugate acids and 4-methylphenol

Now, we will compare the pKa values of the conjugate acids of the anions in the given solutions with the pKa value of 4-methylphenol (10.26). - For aqueous NaOH, the pKa of the conjugate acid (15.7) > pKa of 4-methylphenol (10.26) - For aqueous NaHCO3, the pKa of the conjugate acid (6.35) < pKa of 4-methylphenol (10.26) - For aqueous Na2CO3, the pKa of the conjugate acid (10.33) > pKa of 4-methylphenol (10.26)
03

Determine in which solution(s) 4-methylphenol will dissolve

According to the comparisons made in Step 2, in order for 4-methylphenol to dissolve in a solution, the pKa value of the conjugate acid of the anion present in the solution should be lower than the pKa value of 4-methylphenol. Therefore, 4-methylphenol will dissolve in: (a) Aqueous NaOH

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Most popular questions from this chapter

Complete a net ionic equation for each proton-transfer reaction using curved arrows to show the flow of electron pairs in each reaction. In addition, write Lewis structures for all starting materials and products. Label the original acid and its conjugate base; label the original base and its conjugate acid. If you are uncertain about which substance in each equation is the proton donor, refer to Table \(4.1\) for the relative strengths of proton acids. (a) \(\mathrm{NH}_{3}+\mathrm{HCl} \rightleftharpoons\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{O}^{-}+\mathrm{HCl} \rightleftharpoons\) (c) \(\mathrm{HCO}_{3}^{-}+\mathrm{OH}^{-} \rightleftharpoons\) (d) \(\mathrm{CH}_{3} \mathrm{COO}^{-}+\mathrm{NH}_{4}{ }^{+} \rightleftharpoons\)

Offer an explanation for the following observations. (a) \(\mathrm{H}_{3} \mathrm{O}^{+}\)is a stronger acid than \(\mathrm{NH}_{4}^{+}\). (b) \(\mathrm{Nitric}^{2}\) 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, \(\mathrm{CCl}_{3} \mathrm{COOH}\).

The acid-base chemistry reaction of barium hydroxide \(\left(\mathrm{Ba}(\mathrm{OH})_{2}\right)\) with ammonium thiocyanate \(\left(\mathrm{NH}_{4} \mathrm{SCN}\right)\) in water creates barium thiocyanate, ammonia, and water. The reaction is highly favorable, but is also so endothermic that the solutions cools to such an extent that a layer of frost forms on the reaction vessel. Explain how an endothermic reaction can be favorable.

For each equation, label the Lewis acid and the Lewis base. In addition, show all unshared pairs of electrons on the reacting atoms and use curved arrows to show the flow of electrons in each reaction. (a) \(\mathrm{F}^{-}+\mathrm{BF}_{3} \longrightarrow \mathrm{BF}_{4}^{-}\) (b) C=C[C+]C=[OH+]

Acetic acid, \(\mathrm{CH}_{3} \mathrm{COOH}\), is a weak organic acid, \(\mathrm{p} K_{\mathrm{a}} 4.76\). Write an equation for the equilibrium reaction of acetic acid with each base. Which equilibria lie considerably toward the left? Which lie considerably toward the right? (a) \(\mathrm{NaHCO}_{3}\) (b) \(\mathrm{NH}_{3}\) (c) \(\mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{NaOH}\)
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