Consider the reaction between carbon dioxide and water to form carbonic acid (CH2O3):


CO2(𝑔)+H2O(𝑙)⇌CH2O3(𝑎𝑞)


In the ocean, carbonic acid immediately dissociates to form a proton and bicarbonate ion, as follows:


CH2O3(𝑎𝑞)⇌CHO3−(𝑎𝑞)+H+(𝑎𝑞)


As atmospheric CO2 increases, the ocean absorbs more of the gas. Would this sequence of reactions be driven to the left or the right? How would this affect the pH of the ocean?

Verified step by step guidance

1. Identify the sequence of reactions: First, CO2 reacts with H2O to form carbonic acid (CH2O3). Then, carbonic acid dissociates into bicarbonate ion (CHO3−) and a proton (H+).
2. Understand Le Chatelier's Principle, which states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.
3. Consider the effect of increasing atmospheric CO2: As more CO2 dissolves in the ocean, it shifts the first reaction (CO2 + H2O ⇌ CH2O3) to the right, producing more carbonic acid.
4. Analyze the impact on the second reaction: With more carbonic acid being formed, the reaction (CH2O3 ⇌ CHO3− + H+) is also driven to the right, resulting in increased production of bicarbonate ions and protons.
5. Evaluate the effect on ocean pH: The increase in protons (H+) in the ocean lowers the pH, making the ocean more acidic.

Key Concepts

Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change. In the context of the reaction between carbon dioxide and water, an increase in CO2 concentration will shift the equilibrium to the right, favoring the formation of carbonic acid and its dissociation products.

Acid-Base Chemistry

Acid-base chemistry involves the study of proton donors (acids) and proton acceptors (bases). In the oceanic reaction, carbonic acid (H2CO3) acts as a weak acid, dissociating into bicarbonate (HCO3-) and protons (H+). The increase in H+ concentration from this dissociation leads to a decrease in pH, making the ocean more acidic.

Ocean Acidification

Ocean acidification refers to the process by which the ocean becomes more acidic due to increased levels of CO2 in the atmosphere. As CO2 dissolves in seawater, it forms carbonic acid, which dissociates to release protons, lowering the pH. This phenomenon can have detrimental effects on marine life, particularly organisms that rely on calcium carbonate for their shells and skeletons.