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Chapter 16: Problem 26

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) \(\mathrm{HCO}_{3}^{-}(a q)+\mathrm{F}(a q) \rightleftharpoons\)

Short Answer

Expert verified
(a) \(\mathrm{NH}_{3}(a q) + \mathrm{H}_{2}\mathrm{O}(l)\), equilibrium lies to the right. (b) \(\mathrm{CH}_{3}\mathrm{COOH}(a q)+\mathrm{H}_{2}\mathrm{O}(l)\), equilibrium lies to the left. (c) \(\mathrm{HF}(a q) + \mathrm{CO}_{3}^{2-}(a q)\), equilibrium lies to the right.

Step by step solution

01

Identify Acid and Base

In this reaction, we have \(\mathrm{NH}_{4}^{+}(a q)\) and \(\mathrm{OH}^{-}(a q)\). The \(\mathrm{NH}_{4}^{+}\) ion donates a proton and acts as an acid, while the \(\mathrm{OH}^{-}\) ion accepts the proton, functioning as a base.
02

Write the Reaction

Now we can write the reaction: \[ \mathrm{NH}_{4}^{+}(a q) + \mathrm{OH}^{-}(a q) \rightleftharpoons \mathrm{NH}_{3}(a q) + \mathrm{H}_{2}\mathrm{O}(l) \]
03

Compare Ka Values

To determine whether equilibrium favors the left or the right, we will compare the acid dissociation constants (Ka) of the participating acids. In this case, we need the Ka value of \(\mathrm{NH}_{4}^{+}\). The pKa of \(\mathrm{NH}_{4}^{+}\) is 9.25. The pKb of \(\mathrm{OH}^{-}\) is 0.74. Since the pKa of \(\mathrm{NH}_{4}^{+}\) is greater than the pKb of \(\mathrm{OH}^{-}\), equilibrium lies to the right. (b)
04

Identify Acid and Base

In this reaction, we have \(\mathrm{CH}_{3} \mathrm{COO}^{-}(a q)\) and \(\mathrm{H}_{3} \mathrm{O}^{+}(a q)\). The \(\mathrm{CH}_{3} \mathrm{COO}^{-}\) ion functions as a base, receiving a proton, while the \(\mathrm{H}_{3} \mathrm{O}^{+}\) ion donates a proton, functioning as an acid.
05

Write the Reaction

Now we can write the reaction: \[ \mathrm{CH}_{3}\mathrm{COO}^{-}(a q)+\mathrm{H}_{3}\mathrm{O}^{+}(a q)\rightleftharpoons \mathrm{CH}_{3}\mathrm{COOH}(a q)+\mathrm{H}_{2}\mathrm{O}(l) \]
06

Compare Ka Values

To determine whether equilibrium favors the left or the right, we will compare the acid dissociation constants of the acids. We need the Ka value of \(\mathrm{CH}_{3}\mathrm{COOH}\) and the Kb value of \(\mathrm{CH}_{3} \mathrm{COO}^{-}\). The Ka of \(\mathrm{CH}_{3}\mathrm{COOH}\) is \(1.8 \times 10^{-5}\), and the Kb of \(\mathrm{CH}_{3} \mathrm{COO}^{-}\) is \(5.6\times 10^{-10}\). Since the Ka of \(\mathrm{CH}_{3}\mathrm{COOH}\) is greater than the Kb of \(\mathrm{CH}_{3} \mathrm{COO}^{-}\), equilibrium lies to the left. (c)
07

Identify Acid and Base

In this reaction, we have \(\mathrm{HCO}_{3}^{-}(a q)\) and \(\mathrm{F}^{-}(a q)\). The \(\mathrm{HCO}_{3}^{-}\) ion can donate a proton, acting as an acid, while the \(\mathrm{F}^{-}\) ion can accept a proton, functioning as a base.
08

Write the Reaction

Now we can write the reaction: \[ \mathrm{HCO}_{3}^{-}(a q) + \mathrm{F}^{-}(a q) \rightleftharpoons \mathrm{HF}(a q) + \mathrm{CO}_{3}^{2-}(a q) \]
09

Compare Ka Values

To determine whether equilibrium favors the left or the right, we will compare the acid dissociation constants of the participating acids. In this case, we need the Ka value of \(\mathrm{HCO}_{3}^{-}\) and the Ka value of \(\mathrm{HF}\). The pKa of \(\mathrm{HCO}_{3}^{-}\) is 6.37, and the pKa of \(\mathrm{HF}\) is 3.17. Since the pKa of \(\mathrm{HCO}_{3}^{-}\) is greater than the pKa of \(\mathrm{HF}\), equilibrium lies to the right. In conclusion, the equilibria of the given reactions are as follows: (a) Equilibrium lies to the right (b) Equilibrium lies to the left (c) Equilibrium lies to the right

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Most popular questions from this chapter

codeine \(\left(\mathrm{C}_{18} \mathrm{H}_{21} \mathrm{NO}_{3}\right)\) is a weak organic base. \(\mathrm{A} 5.0 \times 10^{-3} \mathrm{M}\) solution of codeine has a pH of \(9.95 .\) Calculate the value of \(K_{b}\) for this substance. What is the \(\mathrm{pK}_{b}\) for this base?

At the freezing point of water \(\left(0^{\circ} \mathrm{C}\right), K_{w}=1.2 \times 10^{-15}\) Calculate \(\left[\mathrm{H}^{+}\right]\) and \(\left[\mathrm{OH}^{-}\right]\) for a neutral solution at this temperature.

Indicate whether each of the following statements is true or false. For each statement that is false, correct the statement to make it true. (a) Acid strength in a series of \(\mathrm{H}-\) A molecules increases with increasing size of \(\mathrm{A} .\) (b) For acids of the same general structure but differing electronegativities of the central atoms, acid strength decreases with increasing electronegativity of the central atom.(c) The strongest acid known is HF because fluorine is the most electronegative element.

Label each of the following as being a strong acid, a weak acid, or a species with negligible acidity. In each case write the formula of its conjugate base, and indicate whether the conjugate base is a strong base, a weak base, or a species with negligible basicity: \((\mathbf{a}) \mathrm{HCOOH}\), \((\mathbf{b})\mathrm{H}_{2},(\mathrm{c}) \mathrm{CH}_{4},(\mathbf{d}) \mathrm{HF},(\mathbf{e}) \mathrm{NH}_{4}^{+}\)

(a) Write a chemical equation that illustrates the auto-ionization of water. (b) Write the expression for the ion-product constant for water \(K_{w}\) . (c) If a solution is described as basic, which of the following is true: (i) \(\left[\mathrm{H}^{+}\right]>\left[\mathrm{OH}^{-}\right],\) (ii) \(\left[\mathrm{H}^{+}\right]=\left[\mathrm{OH}^{-}\right],\) or (iii) \(\left[\mathrm{H}^{+}\right]<\left[\mathrm{OH}^{-}\right] ?\)
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