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Chapter 13: Problem 62

Ascorbic acid, \(\mathrm{H}_{2} \mathrm{C}_{6} \mathrm{H}_{6} \mathrm{O}_{6}\), also known as vitamin \(\mathrm{C}\), is present in many citrus fruits. It is a diprotic acid with the following \(K_{\mathrm{a}}\) values: \(K_{\mathrm{al}}=7.9 \times 10^{-5}\); \(K_{\mathrm{a} 2}=1.6 \times 10^{-12}\). What is the \(\mathrm{pH}\) of a \(0.63 \mathrm{M}\) solution of ascorbic acid? Estimate \(\left[\mathrm{HC}_{6} \mathrm{H}_{6} \mathrm{O}_{6}^{-}\right]\) and \(\left[\mathrm{C}_{6} \mathrm{H}_{6} \mathrm{O}_{6}{ }^{2-}\right]\).

Short Answer

Expert verified
Question: Calculate the pH of a 0.63 M solution of ascorbic acid and estimate the concentrations of HC6H6O6- and C6H6O6²⁻, given Ka1 = 7.9 x 10⁻⁵ and Ka2 = 1.6 x 10⁻¹².

Step by step solution

01

Write the ionization steps and the corresponding Ka expressions for ascorbic acid#

The ionization process for ascorbic acid can be described in two steps: 1st ionization step: H2C6H6O6 (aq) <=> H+ (aq) + HC6H6O6⁻ (aq) Ka1 = [H+][HC6H6O6⁻]/[H2C6H6O6] 2nd ionization step: HC6H6O6⁻ (aq) <=> H+ (aq) + C6H6O6²⁻ (aq) Ka2 = [H+][C6H6O6²⁻]/[HC6H6O6⁻] Given that Ka1 = 7.9 x 10⁻⁵ and Ka2 = 1.6 x 10⁻¹².

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Most popular questions from this chapter

WEB The pH of a \(2.642 M\) solution of a weak acid, \(\mathrm{HB}\), is \(5.32\). What is \(K_{\mathrm{a}}\) for the weak acid?

Consider these acids $$\begin{array}{lllll}\hline \text { Acid } & \mathrm{A} & \mathrm{B} & \mathrm{C} & \mathrm{D} \\\K_{\mathrm{a}} & 1.6 \times 10^{-3} & 9 \times 10^{-4} & 2 \times 10^{-6} & 3 \times 10^{-4} \\\\\hline\end{array}$$ (a) Arrange the acids in order of increasing acid strength from weakest to strongest. (b) Which acid has the smallest \(\mathrm{pK}_{\mathrm{a}}\) value?

Find the value of \(K_{\mathrm{a}}\) for the conjugate acid of the following bases. (a) pyridine, a pesticide; \(K_{\mathrm{b}}=1.5 \times 10^{-9}\) (b) aniline, an important dye intermediate; \(K_{\mathrm{b}}=3.8 \times 10^{-10}\)

A student prepares \(455 \mathrm{~mL}\) of a KOH solution, but neglects to write down the mass of KOH added. His TA suggests that he take the \(\mathrm{pH}\) of the solution. The \(\mathrm{pH}\) is \(13.33 .\) How many grams of KOH were added?

According to the Brønsted-Lowry theory, which of the following would you expect to act as an acid? Which as a base? (a) \(\mathrm{CHO}_{2}^{-}\) (b) \(\mathrm{NH}_{4}^{+}\) (c) \(\mathrm{HSO}_{3}^{-}\)
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