Question

) pes) Ocean acidification is a result of increaning Poe (partial pressure of CO) in the atmosphere, When CO dissolves into systems, is in tam increasing the amount of in marine systems marine sysem, in forms carbonie acid (a weak acid) This increasing acidity is a formed from CaCO, (K 45E-9). The solubility of Cac00% is and you want to calculabe the change in solubility with a decrease in marine pt Currently, marine plt is- on pH, a (10 points) Write aWl potential chemical reactions that can occur in this multiple equilibria system. 1 changes are specifically causing an increase in CaCO, dissolation 1 (5 points) Write the K expressions for each reaction above (numbering the reactions and corresponding K expressions, and using the appropriate subscript on each type of K, if needed) b.

Answer 1

a)As we know that CO₂ dissolves in marine water to form Carbonic acid, so the very first reaction would be:

1) $\tiny CO_{2} + H_{2}O\rightleftharpoons H_{2}CO_{3}$

Now, the Carbonic acid formed in the system can dissociate to form the bicarbonate ion,

2) $\tiny H_{2}CO_{3} \rightleftharpoons H^{+} + HCO_{3}^{-}$

And, also the bicarbonate can further dissociate into carbonate ions,

3) $\tiny HCO_{3}^{-} \rightleftharpoons H^{+} + CO_{3}^{2-}$

These are the potential chemical reactions occuring in the Multiple equilibria system.

Now to explain the Dissolution of calcium carbonate, we need to study the net direction of the above reactions.As the CO₂ starts to dissolve, the primary reactions that take place are (1) and (2), that too in the forward direction.Now, we see from equation (2), that the dissolution of CO₂ is causing an increase in hydrogen ion concentration or a decrease in pH.This makes the role of Equation (3) very important.As the H⁺ ion conc. increases, it moves in backward direction to form more bicarbonate ions, so as to decrease H⁺ ions.This leads to Dissolution of Carbonate ions from the CaCO₃ in the coral reefs.

b)      
H2CO3]
...................................(1)

Ka H2CO3]
...................................(2)

         
Ka 2 HCO
....................................(3)