Question

Seashells are mostly calcium carbonate, which reacts with $\left[{\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\right]$according to the equation

${\mathbf{\text{CaCO}}}_{\mathbf{\text{3}}}{\mathbf{\text{(s) +H}}}_{\mathbf{\text{3}}}{\mathbf{\text{O}}}^{\mathbf{\text{+}}}\mathbf{\text{(aq)}}\mathbf{\rightleftharpoons }{\mathbf{\text{Ca}}}^{\mathbf{\text{2 +}}}{\mathbf{\text{(aq) + HCO}}}_{\mathbf{\text{3}}}^{\mathbf{\text{-}}}{\mathbf{\text{(aq) +H}}}_{\mathbf{\text{2}}}\mathbf{\text{O(l)}}$

If${\mathbf{\text{K}}}_{\mathbf{\text{w}}}$ increases at higher pressure, will seashells dissolve more rapidly near the surface of the ocean or at great depths? Explain.

Short answer

The${\text{CaCO}}_3$will dissolve more rapidly at great depths.

Step-by-step solution

To explain

${\text{CaCO}}_{\text{3}}{\text{+H}}_{\text{3}}{\text{O}}^{\text{+}}\rightleftharpoons {\text{Ca}}^{\text{2 +}}{\text{+ HCO}}_{\text{3}}^{\text{-}}{\text{+H}}_{\text{2}}\text{O}$

Note that the equation of${\text{K}}_{\text{w}}$is${\text{K}}_{\text{w}}\text{=}\left[{\text{OH}}^{\text{-}}\right]\left[{\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\right].$

One can observe that the${\text{K}}_{\text{w}}$is directly proportional to the$\left[{\text{H}}_3{\text{O}}^{+}\right]$. So, when the${\text{K}}_{\text{w}}$increases, the$\left[{\text{H}}_3{\text{O}}^{+}\right]$also increases, and an increase will drive the reaction to the right, consuming/dissolving more${\text{CaCO}}_3$. Weknow that pressure in water increases with depth. Therefore, seashells will dissolve more rapidly at great depths. Hence, the${\text{CaCO}}_3$ will also dissolve more rapidly at great depths.