Question

When exposed to air, calcium first forms calcium oxide, which is then converted to calcium hydroxide, and finally to calcium carbonate. Write a balanced equation for each step.

Short answer

1) \(2 \text{Ca} + \text{O}_2 \rightarrow 2 \text{CaO}\), 2) \(\text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2\), 3) \(\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}\).

Step-by-step solution

Formation of Calcium Oxide

When calcium is exposed to oxygen in the air, it reacts to form calcium oxide. The balanced chemical equation for this reaction is: \[ 2 \text{Ca} + \text{O}_2 \rightarrow 2 \text{CaO} \] This shows that two moles of calcium react with one mole of oxygen gas to form two moles of calcium oxide.

Formation of Calcium Hydroxide

The calcium oxide reacts with water in the air to form calcium hydroxide. The balanced chemical equation for this reaction is: \[ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 \] This equation indicates that one mole of calcium oxide reacts with one mole of water to produce one mole of calcium hydroxide.

Formation of Calcium Carbonate

Finally, calcium hydroxide reacts with carbon dioxide in the air to form calcium carbonate. The balanced chemical equation for this reaction is: \[ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \] This equation shows that one mole of calcium hydroxide reacts with one mole of carbon dioxide to form one mole of calcium carbonate and one mole of water.

Key concepts

Calcium Oxide

Calcium oxide, often called quicklime, is a basic oxide that is highly reactive with water and carbon dioxide. It is formed when calcium reacts with oxygen from the air. The energy released in this reaction makes it a type of exothermic reaction, meaning it produces heat.

The chemical equation is:

• \[ 2 \text{Ca} + \text{O}_2 \rightarrow 2 \text{CaO} \]

This equation shows that two moles of calcium (Ca) react with one mole of oxygen gas (\(\text{O}_2\)) to produce two moles of calcium oxide (\(\text{CaO}\)).

Calcium oxide is an important industrial chemical, widely used in the manufacture of cement, paper, and steel. It's essential to protect it from moisture, as it reacts readily with water, forming calcium hydroxide. That leads us to the next step in the cycle when this oxide meets water molecules.

Calcium Hydroxide

When calcium oxide combines with water, it transforms into a new compound called calcium hydroxide or slaked lime. This reaction is highly exothermic, releasing considerable heat. The balanced equation showcasing this process is:

• \[ \text{CaO} + \text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 \]

One mole of calcium oxide (\(\text{CaO}\)) reacts with one mole of water (\(\text{H}_2\text{O}\)) to yield one mole of calcium hydroxide (\(\text{Ca(OH)}_2\)).

This compound has antiseptic and disinfectant properties, making it a useful substance in a variety of industries, like water purification and plaster production. The creation of calcium hydroxide is a crucial step before converting to calcium carbonate. This transformation occurs when calcium hydroxide interacts with carbon dioxide in the air.

Calcium Carbonate

Finally, calcium hydroxide undergoes a reaction with carbon dioxide in the air to form calcium carbonate. This compound is commonly found in rocks as minerals like calcite and aragonite. The balanced chemical equation for this conversion is:

• \[ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \]

This indicates that one mole of calcium hydroxide (\(\text{Ca(OH)}_2\)) combines with one mole of carbon dioxide (\(\text{CO}_2\)) resulting in one mole of calcium carbonate (\(\text{CaCO}_3\)) and one mole of water (\(\text{H}_2\text{O}\)).

Calcium carbonate is widely used as a building material and is a primary component of limestone, marble, and chalk. It is also used in the pharmaceutical industry as a calcium supplement as well as an antacid. This final stage of reaction demonstrates the natural cycle of how calcium compounds evolve when exposed to environmental elements.