The Formation of Calcium Carbonate When Carbon Dioxide is Passed Through Lime Water

When carbon dioxide is passed through lime water, a fascinating chemical reaction occurs, resulting in the formation of a milky white precipitate known as calcium carbonate. Calcium carbonate (CaCO3) has a wide range of industrial applications, from whitewashing walls to the production of cement. In this article, we will explore the science behind this reaction and its practical applications.

Chemical Reaction Overview

The reaction between carbon dioxide and lime water can be broken down into a series of steps. Initially, lime water, which is a saturated solution of calcium hydroxide (Ca(OH)2) in water, reacts with carbon dioxide (CO2) to form calcium carbonate and water:

Step 1: Calcium Carbonate Formation

Ca(OH)2(aq) CO2(g) → CaCO3(s) H2O(l)

This initial reaction results in the precipitation of calcium carbonate as a solid, giving the solution a milky appearance due to the presence of the white precipitate. Calcium carbonate is essentially insoluble in water, with a solubility of only 13 ppm (parts per million).

Step 2: Conversion to Calcium Bicarbonate

As more carbon dioxide is introduced into the solution, the calcium carbonate transforms into calcium bicarbonate (Ca(HCO3)2), which is soluble in water:

CaCO3(s) H2O(l) CO2(g) → Ca(HCO3)2(aq)

This second reaction causes the milky solution to disappear, leaving a clear liquid that is rich in calcium bicarbonate.

Practical Applications

Understanding this chemical reaction is crucial for various industrial and scientific applications:

Whitewashing

One of the most common uses of this reaction is in the whitewashing of walls. Calcium carbonate, due to its white color and high reactivity, can effectively cover walls with a protective and aesthetic layer. This process is simple and cost-effective, making it a popular choice for many households and construction projects.

Cement Production

The formation of calcium carbonate is a critical part of the cement production process. During the manufacturing of cement, a significant amount of calcium carbonate is driven off, which contributes to the overall strength and durability of the cement when it is set. Over time, the calcium carbonate that is part of the soil and rocks mixes back into the environment, completing the natural cycle.

How to Prepare Lime Water

Lime water, which is a saturated solution of calcium hydroxide, can be easily prepared at home for experimental purposes:

Obtain calcium hydroxide (Ca(OH)2) from a reliable source. This can be obtained from common hardware stores or online suppliers.

Fill a clean glass jar (up to 1 gallon) with distilled or filtered water.

Slowly add 1 teaspoon of calcium hydroxide to the water and stir thoroughly.

Shake the jar vigorously for 1 to 2 minutes to ensure the calcium hydroxide is fully dispersed.

Leave the jar standing for 24 hours at room temperature. It is normal to observe sediment at the bottom of the jar, which is a result of the calcium hydroxide that did not dissolve.

Conclusion

The reaction between carbon dioxide and lime water is a prime example of a chemical process that has practical and industrial applications. By understanding the science behind this reaction, we can appreciate the role of chemistry in everyday life and the environment.

References

Limewater - Wikipedia Calcium Hydroxide Solubility (1730 ppm), Calcium Carbonate Solubility (13 ppm) - Various Sources

Note: The provided references and sources can be expanded for a more comprehensive article.