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Chapter 16: Problem 107

Oxalic acid \(\left(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\right)\) is a diprotic acid. By using data in Appendix \(\mathrm{D}\) as needed, determine whether each of the following statements is true: (a) \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\) can serve as both a Bronsted-Lowry acid and a Brønsted-Lowry base. (b) $\mathrm{C}_{2} \mathrm{O}_{4}^{2-}\( is the conjugate base of \)\mathrm{HC}_{2} \mathrm{O}_{4}^{-}$. (c) An aqueous solution of the strong electrolyte \(\mathrm{KHC}_{2} \mathrm{O}_{4}\) will have \(\mathrm{pH}<7\).

Short Answer

Expert verified
All three statements (a), (b), and (c) are true. Oxalic acid (H2C2O4) can serve as both a Brønsted-Lowry acid and base. The doubly deprotonated species (C2O42-) is the conjugate base of the singly deprotonated species (HC2O4-). An aqueous solution of KHC2O4 will have a pH less than 7.

Step by step solution

01

Part a: Determine if H2C2O4 is both an acid and base according to Brønsted-Lowry theory

A Brønsted-Lowry acid is a substance that donates a proton (H+) to another substance (the base). A Brønsted-Lowry base is a substance that accepts a proton from another substance (the acid). Oxalic acid (H2C2O4) is a diprotic acid, meaning it can donate two protons. When it donates one proton, it forms the singly deprotonated species HC2O4-: H2C2O4 (acid) + H2O (base) → HC2O4- (conjugate base) + H3O+ (conjugate acid) Since HC2O4- can accept a proton to revert to H2C2O4, it can act as a Brønsted-Lowry base. Hence, oxalic acid can serve as both a Brønsted-Lowry acid and base. The statement is true.
02

Part b: Determine if C2O42- is the conjugate base of HC2O4-

The conjugate base is formed when an acid loses a proton. As discussed in part a, when H2C2O4 loses a proton, it forms HC2O4-: H2C2O4 (acid) + H2O (base) → HC2O4- (conjugate base) + H3O+ (conjugate acid) If HC2O4- loses another proton, it forms the doubly deprotonated species C2O42-: HC2O4- (acid) + H2O (base) → C2O42- (conjugate base) + H3O+ (conjugate acid) Thus, C2O42- is the conjugate base of HC2O4-. The statement is true.
03

Part c: Determine if an aqueous solution of KHC2O4 will have pH < 7

When KHC2O4 is added to water, it dissociates into its constituent ions: KHC2O4 → K+ + HC2O4- Since K+ is a cation from a strong base (KOH), it does not affect the pH of the solution. However, HC2O4- is a weak acid formed by the deprotonation of the oxalic acid and will dissociate as follows: HC2O4- (acid) + H2O (base) ↔ C2O42- (conjugate base) + H3O+ (conjugate acid) This reaction produces H3O+ ions, which increase the hydronium ion concentration in the solution, resulting in a pH value that is less than 7. The statement is true. In summary, all three statements (a), (b), and (c) are true based on the Brønsted-Lowry theory and properties of oxalic acid.

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Most popular questions from this chapter

The hypochlorite ion, \(\mathrm{ClO}^{-}\), acts as a weak base. (a) Is ClO a stronger or weaker base than hydroxylamine? (b) When \(\mathrm{ClO}^{-}\) acts as a base, which atom, \(\mathrm{Cl}\) or \(\mathrm{O}\), acts as the proton acceptor? (c) Can you use formal charges to rationalize your answer to part (b)?

At \(50^{\circ} \mathrm{C}\), the ion-product constant for $\mathrm{H}_{2} \mathrm{O}\( has the value \)K_{w}=5.48 \times 10^{-14} \cdot(\mathbf{a})$ What is the \(\mathrm{pH}\) of pure water at \(50^{\circ} \mathrm{C} ?\) (b) Based on the change in \(K_{w}\) with temperature, predict whether \(\Delta H\) is positive, negative, or zero for the autoionization reaction of water: $$ 2 \mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{OH}^{-}(a q) $$

Based on their compositions and structures and on conjugate acid-base relationships, select the stronger base in each of the following pairs: (a) \(\mathrm{NO}_{3}^{-}\) or \(\mathrm{NO}_{2}^{-},\) (b) \(\mathrm{PO}_{4}^{3-}\) or \(\mathrm{AsO}_{4}^{3-}\), (c) \(\mathrm{HCO}_{3}^{-}\) or \(\mathrm{CO}_{3}^{2-}\).

\(\mathrm{NH}_{3}(g)\) and \(\mathrm{HCl}(g)\) react to form the ionic solid \(\mathrm{NH}_{4} \mathrm{Cl}(s) .\) Which substance is the Brønsted-Lowry acid in this reaction? Which is the Brønsted-Lowry base?

A solution is made by adding $1.000 \mathrm{~g} \mathrm{Ca}(\mathrm{OH})_{2}(s), 100.0 \mathrm{~mL}$ of \(0.10 \mathrm{M} \mathrm{H}_{2} \mathrm{SO}_{4}\), and enough water to make a final volume of \(350.0 \mathrm{~mL}\). Assuming that all of the solid dissolves, what is the \(\mathrm{pH}\) of the final solution?
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