Chapter 19, Problem 98A

Interpretation Introduction

Interpretation: In the case of slightly alkaline seawater, whether the concentration of dissolved carbon dioxide will be higher or lower than in pure water needs to be explained.

Concept Introduction: For any reversible reaction, if the concentration of any species increases at equilibrium, the reaction moves in the direction of neutral the effect of an increase in the concentration.

Explanation of Solution

The four different reversible reactions showing the solubility of carbon dioxide in water are represented as follows:

  $\begin{array}{l}{\text{CO}}_{\text{2}}\left(g\right)\rightleftharpoons {\text{CO}}_{\text{2}}\left(aq\right)\\ {\text{CO}}_{\text{2}}\left(aq\right)+{\text{H}}_{\text{2}}\text{O}\left(l\right)\rightleftharpoons {\text{H}}_{\text{2}}{\text{CO}}_{\text{3}}\left(aq\right)\\ {\text{H}}_{\text{2}}{\text{CO}}_{\text{3}}\left(aq\right)\rightleftharpoons {\text{H}}^{+}\left(aq\right){\text{+HCO}}_{\text{3}}{}^{-}\left(aq\right)\\ {\text{HCO}}_{\text{3}}{}^{-}\left(aq\right)\rightleftharpoons {\text{H}}^{+}\left(aq\right){\text{+CO}}_{\text{3}}{}^{2-}\left(aq\right)\end{array}$

Here, if water is slightly alkaline, the concentration of hydroxide ions will be more and the formation of hydrogen carbonate will form at higher rates. Here, the sign of a reversible reaction will be more towards a product that is more concentrated of hydrogen carbonate takes place. Here, hydrogen carbonate is a dissolved form of carbon dioxide thus, this results in a higher concentration of dissolved carbon dioxide as compared to pure water.