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Chapter 16: Problem 19

(a) The hydrogen oxalate ion \(\left(\mathrm{HC}_{2} \mathrm{O}_{4}^{-}\right)\) is amphiprotic. Write a balanced chemical equation showing how it acts as an acid toward water and another equation showing how it acts as a base toward water. (b) What is the conjugate acid of \(\mathrm{HC}_{2} \mathrm{O}_{4}\) ? What is its conjugate base?

Short Answer

Expert verified
The hydrogen oxalate ion (\(\mathrm{HC}_{2} \mathrm{O}_{4}^{-}\)) acts as an acid towards water and forms \(\mathrm{C}_{2}\mathrm{O}_{4}^{2-} + \mathrm{H}_{3}\mathrm{O}^{+}\), with a balanced equation: \(\mathrm{HC}_{2}\mathrm{O}_{4}^{-} + \mathrm{H}_{2}\mathrm{O} \rightleftharpoons \mathrm{C}_{2}\mathrm{O}_{4}^{2-} + \mathrm{H}_{3}\mathrm{O}^{+}\). It also acts as a base towards water and forms \(\mathrm{H}_{2}\mathrm{C}_{2}\mathrm{O}_{4} + \mathrm{OH}^{-}\), with a balanced equation: \(\mathrm{HC}_{2}\mathrm{O}_{4}^{-} + \mathrm{H}_{2}\mathrm{O} \rightleftharpoons \mathrm{H}_{2}\mathrm{C}_{2}\mathrm{O}_{4} + \mathrm{OH}^{-}\). The conjugate acid of \(\mathrm{HC}_{2} \mathrm{O}_{4}^{-}\) is \(\mathrm{H}_{2}\mathrm{C}_{2}\mathrm{O}_{4}\), while its conjugate base is \(\mathrm{C}_{2}\mathrm{O}_{4}^{2-}\).

Step by step solution

01

1. Hydrogen oxalate as an acid

When an amphiprotic substance behaves as an acid, it donates a proton (H\(^{+}\)) to the water molecule. The hydrogen oxalate ion (\(\mathrm{HC}_{2}\mathrm{O}_{4}^{-}\)) will lose a proton, forming \(\mathrm{C}_{2}\mathrm{O}_{4}^{2-}\) ion. The balanced chemical equation for this reaction is given by: \(\mathrm{HC}_{2}\mathrm{O}_{4}^{-} + \mathrm{H}_{2}\mathrm{O} \rightleftharpoons \mathrm{C}_{2}\mathrm{O}_{4}^{2-} + \mathrm{H}_{3}\mathrm{O}^{+}\)
02

2. Hydrogen oxalate as a base

As a base, the amphiprotic hydrogen oxalate ion (\(\mathrm{HC}_{2}\mathrm{O}_{4}^{-}\)) will accept a proton from the water molecule. This results in the formation of the ion \(\mathrm{H}_{2}\mathrm{C}_{2}\mathrm{O}_{4}\). The balanced chemical equation for this reaction is given by: \(\mathrm{HC}_{2}\mathrm{O}_{4}^{-} + \mathrm{H}_{2}\mathrm{O} \rightleftharpoons \mathrm{H}_{2}\mathrm{C}_{2}\mathrm{O}_{4} + \mathrm{OH}^{-}\)
03

3. Conjugate acid of \(\mathrm{HC}_{2}\mathrm{O}_{4}^{-}\)

The conjugate acid of a substance is formed when it accepts a proton. In the case of \(\mathrm{HC}_{2}\mathrm{O}_{4}^{-}\), it becomes \(\mathrm{H}_{2}\mathrm{C}_{2}\mathrm{O}_{4}\) after accepting a proton, according to the reaction in step 2. Therefore, the conjugate acid of \(\mathrm{HC}_{2}\mathrm{O}_{4}^{-}\) is \(\mathrm{H}_{2}\mathrm{C}_{2}\mathrm{O}_{4}\).
04

4. Conjugate base of \(\mathrm{HC}_{2}\mathrm{O}_{4}^{-}\)

The conjugate base of a substance is formed when it donates a proton. In the case of \(\mathrm{HC}_{2}\mathrm{O}_{4}^{-}\), it becomes \(\mathrm{C}_{2}\mathrm{O}_{4}^{2-}\) after donating a proton, according to the reaction in step 1. Therefore, the conjugate base of \(\mathrm{HC}_{2}\mathrm{O}_{4}^{-}\) is \(\mathrm{C}_{2}\mathrm{O}_{4}^{2-}\).

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Most popular questions from this chapter

Identify the Lewis acid and Lewis base among the reactants in each of the following reactions: (a) \(\mathrm{Fe}\left(\mathrm{ClO}_{4}\right)_{3}(s)+6 \mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons\) $$ \begin{array}{l} \mathrm{Fe}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}{ }^{3+}(a q)+3 \mathrm{ClO}_{4}^{-}(a q) \\ \text { (b) } \mathrm{CN}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{HCN}(a q)+\mathrm{OH}^{-}(a q) \end{array} $$ (c) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}(g)+\mathrm{BF}_{3}(g) \rightleftharpoons\left(\mathrm{CH}_{3}\right)_{3} \mathrm{NBF}_{3}(s)\) $$ \text { (d) } \mathrm{HIO}(l q)+\mathrm{NH}_{2}^{-}(l q) \rightleftharpoons \mathrm{NH}_{3}(l q)+\mathrm{IO}^{-}(l q) $$ (lq denotes liquid ammonia as solvent)

Write the chemical equation and the \(K_{a}\) expression for the ionization of each of the following acids in aqueous solution. First show the reaction with \(\mathrm{H}^{+}(a q)\) as a product and then with the hydronium ion: (a) \(\mathrm{HBrO}_{2}\), (b) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{COOH}\).

Deuterium oxide \(\left(\mathrm{D}_{2} \mathrm{O},\right.\) where \(\mathrm{D}\) is deuterium, the hydrogen- 2 isotope) has an ion-product constant, \(K_{w^{+}}\) of \(8.9 \times 10^{-16}\) at \(20^{\circ} \mathrm{C}\). Calculate \(\left[\mathrm{D}^{+}\right]\) and \(\left[\mathrm{OD}^{-}\right]\) for pure (neutral) \(\mathrm{D}_{2} \mathrm{O}\) at this temperature.

(a) Given that \(K_{a}\) for acetic acid is \(1.8 \times 10^{-5}\) and that for hypochlorous acid is \(3.0 \times 10^{-8}\), which is the stronger acid? (b) Which is the stronger base, the acetate ion or the hypochlorite ion? (c) Calculate \(K_{b}\) values for \(\mathrm{CH}_{3} \mathrm{COO}^{-}\) and \(\mathrm{ClO}^{-}\).

Ephedrine, a central nervous system stimulant, is used in nasal sprays as a decongestant. This compound is a weak organic base: \(\mathrm{C}_{10} \mathrm{H}_{15} \mathrm{ON}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{C}_{10} \mathrm{H}_{15} \mathrm{ONH}^{+}(a q)+\mathrm{OH}^{-}(a q)\) (a) What A \(0.035 \mathrm{M}\) solution of ephedrine has a pH of 11.33 . are the equilibrium concentrations of \(\mathrm{C}_{10} \mathrm{H}_{15} \mathrm{ON}\), \(\mathrm{C}_{10} \mathrm{H}_{15} \mathrm{ONH}^{+},\) and \(\mathrm{OH}^{-} ?\) (b) Calculate \(K_{b}\) for ephedrine.
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