Stony corals secrete thin layers of calcium carbonate (CaCO3) to build the foundation of coral reefs. The relationship between calcium carbonate, carbonic acid, and calcium bicarbonate (Ca(HCO3)2) is shown below:

CH2O3(𝑎𝑞)+CaCO3(𝑠) ⇌ Ca(HCO3)2(𝑎𝑞)

Predict what will happen to the calcium carbonate foundation of reefs as CO2 levels rise in the oceans.

Verified step by step guidance

Understand the chemical reaction: The reaction CH2O3(aq) + CaCO3(s) ⇌ Ca(HCO3)2(aq) shows that carbonic acid (CH2O3) reacts with calcium carbonate (CaCO3) to form calcium bicarbonate (Ca(HCO3)2).

Recognize the source of carbonic acid: Carbonic acid forms when carbon dioxide (CO2) dissolves in water. As CO2 levels in the ocean increase, more CO2 dissolves, forming more carbonic acid.

Analyze the effect on the reaction: With more carbonic acid in the ocean, the reaction is pushed to the right, according to Le Chatelier's Principle, which states that a system at equilibrium will adjust to counteract a change in conditions.

Predict the impact on calcium carbonate: As the reaction shifts to the right, more calcium carbonate (CaCO3) is converted into calcium bicarbonate (Ca(HCO3)2).

Consider the ecological consequences: The dissolution of calcium carbonate weakens the structural integrity of coral reefs, potentially leading to their degradation as CO2 levels continue to rise.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Calcium Carbonate Chemistry

Calcium carbonate (CaCO3) is a key component of coral reefs, providing structural integrity. It can dissolve in acidic conditions, which occurs when carbon dioxide (CO2) reacts with water to form carbonic acid (H2CO3). This process can lead to the formation of bicarbonate ions (Ca(HCO3)2), impacting the availability of calcium carbonate for coral growth.

Ocean Acidification

Ocean acidification refers to the decrease in pH levels of ocean water due to increased CO2 absorption. As CO2 levels rise, more carbonic acid is formed, which lowers the pH and increases the acidity of seawater. This change in acidity can hinder the ability of corals to secrete calcium carbonate, ultimately threatening the stability of coral reef ecosystems.

Coral Reef Ecosystem Dynamics

Coral reefs are complex ecosystems that rely on the balance between calcium carbonate deposition and dissolution. Healthy reefs depend on the ability of corals to build their structures through calcium carbonate secretion. Disruptions in this balance, such as those caused by rising CO2 levels, can lead to reef degradation, affecting biodiversity and the services reefs provide to marine life and human communities.

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Coral Reefs

Related Practice

Textbook Question

From what you have learned about water, why do coastal regions tend to have milder climates with cooler summers and warmer winters than do inland areas at the same latitude?

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Textbook Question

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?

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Open Question

The current average pH of our oceans is 8.1. What is the concentration of protons in the oceans? How has the proton concentration changed in our oceans when compared to before the industrial revolution, when the average pH was 8.2? Express this change as a percentage increase.

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Open Question

Data from the preceding experiment were collected at different times throughout each day over a period of one year under both present-day and estimated year 2100 conditions. Averages from these samples are provided in the following graph

Using the equation in Question 13, what do the positive and negative values indicate in terms of the directionality of this reaction? What implications do these data have on reef stability in the year 2100 if there is no intervention?

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