Problem 146 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following elements occur as their chlorides in earth crust ? (a) \(\mathrm{Na}\) (b) \(\mathrm{Cu}\) (c) \(\mathrm{Ag}\) (d) \(\mathrm{K}\)

Step-by-Step Solution

Answer

Elements (a) Na and (d) K occur as their chlorides in the earth's crust.

Step 1: Identifying Common Chloride Compounds

First, recall that common chloride compounds are often found with alkali metals or similar reactive metals. For example, sodium chloride (NaCl) is well-known as table salt, and potassium chloride (KCl) is another prominent compound.

Step 2: Analyzing Each Element

- **Sodium (Na):** Forms sodium chloride (NaCl), commonly found in the earth's crust. - **Copper (Cu):** Usually found as various sulfide ores, but its chloride forms are not as common in the earth's crust. - **Silver (Ag):** Usually found in pure form or as sulfide compounds, not notably as chlorides in the earth's crust. - **Potassium (K):** Forms potassium chloride (KCl), another salt found commonly.

Step 3: Concluding Based on Analysis

Based on the common occurrence of chlorides in the earth's crust, sodium (Na) and potassium (K) primarily form stable chloride compounds that are prevalent. Copper (Cu) and silver (Ag) do not typically occur as chlorides in nature.

Key Concepts

Sodium Chloride

Sodium chloride, commonly known as table salt, is one of the most prevalent compounds in nature. It occurs naturally and plays a significant role in various geological and biological processes.
This compound is a product of sodium (Na), a highly reactive alkali metal, and chlorine (Cl), a halogen element. Sodium chloride is abundantly found in:

• Oceans and seas, where it comprises about 3% of their total weight
• Various layers of the earth's crust, particularly in salt mines
• Salt flats and salt pans, which are the remnants of evaporated bodies of water

The wide occurrence of sodium chloride is due to its solubility in water and its ability to precipitate out of solution during evaporation.
This natural recycling makes it an essential element for life on Earth, playing a vital role in maintaining cell health and balance in both humans and animals.

Potassium Chloride

Potassium chloride (KCl) is another major chloride compound found in the earth's crust, closely related to sodium chloride. Potassium, like sodium, is an alkali metal and reacts with chloride to form this stable compound, which is significantly important for both plant and animal life. Potassium chloride is typically found in:

• Mineral deposits such as sylvite (KCl) and carnallite, both of which are mined for potassium fertilizers
• Natural salt deposits, often alongside sodium chloride
• Evaporite rocks, formed from dissolved minerals left behind when bodies of water evaporate

Potassium chloride is a critical nutrient in agriculture, providing essential potassium for plant growth.
This compound helps in regulating various vital plant functions, including water regulation and enzyme activation, emphasizing its importance in nature and our food supply.

Element Occurrence in Nature

Elements such as sodium and potassium naturally form stable chloride compounds that are abundantly present in the earth’s crust. Their occurrence is tied to their chemical properties and reactivity. In nature, chlorides of elements are formed primarily due to:

• The reactivity of alkali metals, which readily combine with chlorine
• The widespread presence of chlorine, making chloride formation a natural outcome
• The solubility of chlorides in water, facilitating their movement and deposition in various environmental contexts

Unlike sodium and potassium, metals like copper and silver typically do not occur as chlorides in nature.
They are more often found as sulfides or in their native states due to their lower reactivity with chlorine. The composition and distribution of these elements and their compounds illustrate the diversity and complexity of geological formations on Earth.