Problem 69 - A Complete Resource Book in Chemistry for JEE Main

Question

One of the elements present in carnalite shows flame colouration. The colour of the flame is (a) green (b) lilac (c) yellow (d) orange

Step-by-Step Solution

Answer

The flame color is lilac.

Step 1: Identifying the Elements

Carnallite is a mineral that has the chemical formula \( KCl \cdot MgCl_2 \cdot 6H_2O \). This means it contains potassium (\( K \)), magnesium (\( Mg \)), chlorine (\( Cl \)), and water (\( H_2O \)). Among these, potassium and sometimes chlorine are known for imparting color to a flame.

Step 2: Research Flame Test

In a flame test, different elements emit characteristic colors when heated. Potassium glows with a lilac or light purple color flame, magnesium does not contribute a color noticeable to the human eye, and chlorine and water do not produce distinctive colors in a flame test.

Step 3: Analyzing the Options

The options given are green, lilac, yellow, and orange. From our knowledge of flame tests, potassium is known to show a lilac color when burnt.

Key Concepts

Carnallite

Carnallite is a unique mineral primarily composed of potassium chloride and magnesium chloride, hydrated naturally with water molecules. Its chemical formula, \( KCl \cdot MgCl_2 \cdot 6H_2O \), reveals the combination of these chemicals. Carnallite is important because it serves as a major source of both potassium and magnesium, which are vital elements in many industrial applications.
A key feature of carnalite is its hygroscopic nature, meaning it can absorb moisture from the air. This property makes it useful in various chemical processes where maintaining moisture balance is crucial.

Potassium

Potassium is an alkali metal and one of the most reactive elements in the periodic table. It's characterized by its light, silvery appearance and propensity to react vigorously with water to produce hydrogen gas and potassium hydroxide.
In carnalite, potassium is a significant component, contributing to its properties and uses. Potassium is vital in various biological functions, including muscle function and nerve signal transmission. In agriculture, potassium compounds are extensively used as fertilizers due to their role in plant growth.

Flame Coloration

Flame coloration is a fascinating phenomenon used in chemistry to identify elements based on the color they emit when heated. When an element burns, its electrons become excited and then release energy as they return to their original state.

• Potassium: Lilac flame
• Strontium: Red flame
• Copper: Green flame

These characteristic colors help scientists and educators identify and confirm the presence of specific metals in compounds or materials. Potassium's lilac flame is a distinctive marker that easily distinguishes it from other elements during flame tests.

Chemical Compounds

Chemical compounds are substances formed when two or more elements are chemically bonded together. These compounds often have properties distinctly different from their constituent elements. In the case of carnalite, the combination of potassium, magnesium, and chlorine produces a mineral with unique qualities that don't reflect the individual elements alone.
Understanding chemical compounds is key to harnessing their uses, such as how carnalite's composition makes it particularly valuable as a source of potassium in commercial applications.

Minerals

Minerals are naturally occurring, inorganic solids with a specific chemical composition and a crystalline structure. They form through geological processes and have distinct physical properties, such as color, hardness, and crystal form.
Carnallite, being a mineral, is valued for its chemical components. It is extracted and processed from evaporite deposits found in salt mines. Minerals like carnalite play an essential role in various industries, including agriculture and manufacturing, providing essential elements and compounds that are further utilized in production and nutrient supply.