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The Earth’s oceans contain significant amounts of dissolved carbon dioxide - VCE - SSCE Chemistry - Question 6 - 2003 - Paper 1
Question 6
The Earth’s oceans contain significant amounts of dissolved carbon dioxide. The dissolving process can be described by the following chemical equilibria. CO2(g) ⇌ C... show full transcript
Worked Solution & Example Answer:The Earth’s oceans contain significant amounts of dissolved carbon dioxide - VCE - SSCE Chemistry - Question 6 - 2003 - Paper 1
Step 1
Use this information to explain the likely effect of the increasing concentration of atmospheric CO2 on the pH of seawater at the ocean surface.
Answer
As the concentration of atmospheric CO2 increases, the concentration of CO2(aq) in seawater will also increase. According to Le Chatelier's principle, this will push the equilibrium of the reaction
CO2(aq) + H2O(l) ⇌ H+(aq) + HCO3−(aq)
to the right, generating more H⁺ ions. As the concentration of H⁺ ions increases, the pH of seawater will decrease, making it more acidic. Thus, rising CO2 levels lead to lower pH levels in ocean water.
Step 2
Step 3
ii. Calculate the concentration of the hydrogen carbonate ion, HCO3−, in fresh blood.
Answer
Using the acid dissociation constant provided:
K_a = rac{[H^+][HCO3^-]}{[CO2]}
We know that:
- =
- = .
Substituting into the equation:
7.9 imes 10^{-7} = rac{(3.98 imes 10^{-8})[HCO3^-]}{(1.3 imes 10^{-5})}
Rearranging to solve for gives:
[HCO3^-] = rac{(7.9 imes 10^{-7}) imes (1.3 imes 10^{-5})}{3.98 imes 10^{-8}}
Calculating results in approximately: