Problem 46 - A Complete Resource Book in Chemistry for JEE Main

Question

Mortar is a mixture of (a) slaked lime + silica \(+\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{CaCO}_{3}+\) silica \(+\mathrm{H}_{2} \mathrm{O}\) (c) slaked lime + plaster of paris \(+\mathrm{H}_{2} \mathrm{O}\) (d) plaster of paris + silica

Step-by-Step Solution

Answer

Mortar is a mixture of (a) slaked lime + silica + water.

Step 1: Identify Mortar Components

Mortar is traditionally known as a combination of slaked lime, which is chemically known as calcium hydroxide \(\text{Ca(OH)}_2\), and sand (silica), combined with water \(\text{H}_2\text{O}\).

Key Concepts

Slaked Lime

Slaked lime is another name for calcium hydroxide, a compound represented by the chemical formula \( \text{Ca(OH)}_2 \). It's created by adding water to quicklime (calcium oxide \( \text{CaO} \)). This process, known as slaking, transforms quicklime into a fine, white powder or a thick slurry. Slaked lime is often used in construction for making mortar and plaster.
Here are some characteristics of slaked lime:

• It's slightly soluble in water, forming a clear, colorless limewater solution.
• It reacts with carbon dioxide in the air to form calcium carbonate, a process essential in hardening mortar.
• It's an alkaline substance, which means it has a high pH. This property helps in neutralizing acids.

Slaked lime plays a critical role in building because when it is mixed with water and sand, it forms a sticky paste that helps bind construction materials together. This mixture gradually hardens due to the reaction with carbon dioxide, providing structural strength.

Calcium Hydroxide

Calcium hydroxide, known as slaked lime, is a white, caustic, and alkaline compound. Chemically denoted as \( \text{Ca(OH)}_2 \), it is produced when calcium oxide is hydrated. There are several important uses for calcium hydroxide, particularly in construction and industrial applications.

**Applications of Calcium Hydroxide:**

• **Mortar and Plaster:** In construction, calcium hydroxide is invaluable for making mortars and plasters. It combines with sand and other materials to form a paste that hardens, providing durability.
• **Water Treatment:** Often used to soften water by removing carbonate hardness. It helps in adjusting the pH of water to prevent corrosion in pipes.
• **Soil Stabilization:** Calcium hydroxide is used to improve soil for agriculture by altering its properties to make it more suitable for growing plants.

These uses highlight how calcium hydroxide's chemical properties make it an essential compound in various fields. Its ability to react with other substances is what makes calcium hydroxide so versatile.

Silica

Silica, or silicon dioxide \( \text{SiO}_2 \), is a common compound found in nature as quartz. It is a major constituent of sand, making it an important component in construction materials, including mortar and concrete. Silica provides structural support and durability to these mixtures.

Here's a look at silica's significant roles and properties:

• **Construction Use:** In masonry and building, silica is crucial for making durable, long-lasting mortars and concretes. It helps to bind components together, providing strength and stability.
• **Chemical Durability:** Silica is well known for its resistance to high temperatures and chemical wear, making it ideal for construction materials that need to endure harsh conditions.
• **Natural Abundance:** As one of the most abundant minerals on earth, silica is readily available, which makes it a cost-effective solution for many industries.

The integration of silica in building materials highlights its importance in providing resilience and longevity, ensuring constructed structures last through time and environmental stresses.