Chemistry 2e · 14.5 Polyprotic Acids

Polyprotic Acids: practice problems

3 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

1. Exercises 72

   Which of the following concentrations would be practically equal in a calculation of the equilibrium concentrations in a 0.134-M solution of H₂CO₃, a diprotic acid: $[{\text{H}}_3{\text{O}}^{\text{+}}],$ [OH⁻], [H₂CO₃], $[{\text{HCO}}_3{}^{\text{-}}],$ $[{\text{CO}}_3{}^{2-}]?$ No calculations are needed to answer this question.

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2. Exercises 74

   Calculate the concentration of each species present in a 0.010-M solution of phthalic acid, C₆H₄(CO₂H)₂.

   $\begin{array}{l}\\ {\text{C}}_6{\text{H}}_4{({\text{CO}}_2\text{H})}_2(aq)+{\text{H}}_2\text{O}(l)\rightleftharpoons {\text{H}}_3{\text{O}}^{\text{+}}(aq)+{\text{C}}_6{\text{H}}_4({\text{CO}}_2\text{H}){({\text{CO}}_2)}^{\text{-}}(aq)K_{\text{a}}=1.1\times {10}^{-3}\\ {\text{C}}_6{\text{H}}_4({\text{CO}}_2\text{H})({\text{CO}}_2){}^{-}(aq)+{\text{H}}_2\text{O}(l)\rightleftharpoons {\text{H}}_3{\text{O}}^{\text{+}}(aq)+{\text{C}}_6{\text{H}}_4{({\text{CO}}_2)}_2{}^{2-}(aq)K_{\text{a}}=3.9\times {10}^{-6}\end{array}$

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3. Exercises 76

   The ion HTe⁻ is an amphiprotic species; it can act as either an acid or a base.

   (a) What is K${}_a$ for the acid reaction of HTe⁻ with H₂O?

   (b) What is K${}_b$ for the reaction in which HTe⁻ functions as a base in water?

   (c) Demonstrate whether or not the second ionization of H₂Te can be neglected in the calculation of [HTe⁻] in a 0.10 M solution of H₂Te.

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