Question

What happens when (i) magnesium is burnt in air (ii) quick lime is heated with silica (iii) chlorine reacts with slaked lime (iv) calcium nitrate is heated ?

Short answer

(i) Magnesium forms magnesium oxide; (ii) quick lime and silica form calcium silicate; (iii) chlorine with slaked lime produces bleaching powder; (iv) calcium nitrate decomposes to calcium oxide, nitrogen dioxide, and oxygen.

Step-by-step solution

Understand Magnesium Burning in Air

When magnesium burns in air, it reacts with oxygen to form magnesium oxide. This is represented by the chemical equation: \[ 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \] This is an exothermic reaction, releasing a bright white flame.

Analyze Reaction of Quick Lime with Silica

Quick lime, or calcium oxide (CaO), reacts with silica, or silicon dioxide (SiO₂), to form calcium silicate. This reaction can be represented as: \[ \text{CaO} + \text{SiO}_2 \rightarrow \text{CaSiO}_3 \] Calcium silicate is often used in construction materials.

Explore Chlorine Reacting with Slaked Lime

When chlorine gas reacts with slaked lime or calcium hydroxide \((\text{Ca(OH)}_2)\), bleaching powder is produced along with water. The reaction is: \[ 2\text{Ca(OH)}_2 + 2\text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{CaCl}_2 + 2\text{H}_2\text{O} \] This forms a mixture that is used as a disinfectant.

Detail Heating of Calcium Nitrate

When calcium nitrate \((\text{Ca(NO}_3)_2)\) is heated, it decomposes to form calcium oxide, nitrogen dioxide, and oxygen gas. The reaction can be represented as: \[ 2\text{Ca(NO}_3)_2 \rightarrow 2\text{CaO} + 4\text{NO}_2 + \text{O}_2 \] The brown gas \(\text{NO}_2\) is released during this decomposition.

Key concepts

Magnesium Oxide Formation

Magnesium oxide formation occurs when magnesium metal is combusted in air. During this reaction, magnesium reacts vigorously with oxygen to form magnesium oxide \(\text{MgO}\). This chemical process is both exothermic and spectacular, characterized by a bright white flame and considerable heat release.
When you represent it as a chemical equation, it looks like this: \[ 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \]
Magnesium oxide has useful properties, such as high thermal stability and insulating abilities, making it valuable in industries like ceramics and electrical insulation. However, it's important to handle magnesium carefully due to its reactive nature, especially when burning, to ensure safety.

Calcium Silicate Production

Calcium silicate is formed when quick lime (calcium oxide) reacts with silica. This kind of transformation is a chemical reaction that yields calcium silicate \(\text{CaSiO}_3\), a compound commonly used in building materials.
Here's the chemical equation for better understanding: \[ \text{CaO} + \text{SiO}_2 \rightarrow \text{CaSiO}_3 \]
Calcium silicate is well-regarded for its fire-resistant properties and is often utilized in insulation material for its ability to withstand high temperatures.

• Fire-resistant qualities make it ideal for construction.
• High thermal insulation helps in energy efficiency.

Such properties contribute to its widespread use in industries seeking durable and heat-tolerant materials.

Bleaching Powder Reaction

The bleaching powder reaction involves chlorine gas \(\text{Cl}_2\) and slaked lime \(\text{Ca(OH)}_2\). This reaction produces bleaching powder \(\text{Ca(OCl)}_2\), a potent disinfectant and whitening agent, along with calcium chloride \(\text{CaCl}_2\) and water.
The chemical equation is as follows: \[ 2\text{Ca(OH)}_2 + 2\text{Cl}_2 \rightarrow \text{Ca(OCl)}_2 + \text{CaCl}_2 + 2\text{H}_2\text{O} \]
Bleaching powder is essential for water purification and sanitizing surfaces because of its strong oxidizing properties. It helps to:

• Disinfect water, making it safe for consumption.
• Sanitize public spaces and households effectively.

It’s a staple in many cleaning and disinfection processes due to its efficiency.

Decomposition of Calcium Nitrate

When calcium nitrate \(\text{Ca(NO}_3)_2\) is heated, it undergoes thermal decomposition. This breakdown results in calcium oxide \(\text{CaO}\), nitrogen dioxide \(\text{NO}_2\), and oxygen \(\text{O}_2\). The brown gas released during this reaction is nitrogen dioxide, known for its characteristic color.
The decomposition equation is represented as: \[ 2\text{Ca(NO}_3)_2 \rightarrow 2\text{CaO} + 4\text{NO}_2 + \text{O}_2 \]
Calcium oxide produced is another form of lime used in various applications, while nitrogen dioxide highlights the hazards of handling such reactions due to its toxicity and environmental impact.

• Calcium oxide serves multi-purpose uses, including soil treatment.
• Nitrogen dioxide needs careful management due to health concerns.

Understanding this decomposition helps in safe practical application and environmental management.