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

Short answer

The flame coloration of Carnalite is lilac due to potassium.

Step-by-step solution

Identify the Elements Present in Carnalite

Carnalite, also known as carnallite, is a mineral composed of hydrated potassium-magnesium chloride, with the formula KCl·MgCl2·6H2O. It comprises three main elements: potassium (K), magnesium (Mg), and chlorine (Cl).

Determine Which Element Causes Flame Colouration

In chemistry, certain elements are known to produce characteristic flame colors when heated. These colors assist in identifying the element. Potassium (K) is known to emit a lilac or pale violet flame in flame tests.

Match the Element with Flame Color Options

Based on the flame test knowledge, potassium causes a lilac flame color. Among the options given (a) Green, (b) Lilac, (c) Yellow, (d) Orange, the color 'Lilac' matches the flame colouration caused by potassium.

Key concepts

Carnalite composition

Carnalite is a fascinating mineral with a unique chemical makeup. It's often referred to in its mineral form as *carnallite*. The scientific formula for carnalite is \( \text{KCl} \cdot \text{MgCl}_2 \cdot 6\text{H}_2\text{O} \). Its composition includes three primary elements:

• Potassium (K): A significant component which plays a crucial role in its mineral structure.
• Magnesium (Mg): This element is also present and contributes to the chemical and physical properties of carnalite.
• Chlorine (Cl): Present as part of both the potassium and magnesium chloride components.

Overall, this combination of elements forms a mineral that is not only important industrially but also has interesting chemical properties. Carnalite is often mined for its potassium content, which is essential in agricultural fertilizers. The hydration aspect, indicated by the \( 6\text{H}_2\text{O} \), means that each formula unit of carnalite is associated with six water molecules, giving it the distinct nature of being a hydrated mineral.

Potassium flame color

When heated, certain elements emit distinct flame colors which can be used for their identification. Potassium is one such element, widely known for its characteristic flame coloration. Understanding the Flame Test for Potassium:
When potassium is burned, it emits a "lilac" or pale violet color. This is due to the electron transitions within the potassium atom. In a flame, electrons in potassium atoms gain energy and move to a higher energy level. When they return to their original state, they release this energy in the form of light, which we observe as a lilac flame. This unique lilac hue is essential for distinguishing potassium from other elements during a flame test, making it a reliable method in educational and professional settings alike. Flame tests offer a quick way to identify the presence of specific elements based on their flame colors, with potassium’s lilac being one of the most distinctive.

Chemical identification methods

Chemical identification often involves simple, yet effective, techniques such as flame tests to discern the presence of certain elements. These methods provide visual cues that help distinguish between different chemical substances. Flame Test Basics:
The flame test is a qualitative analysis technique used to identify elements, especially metals. When a sample of an element is vaporized in a flame, the electrons become excited and then drop back to lower energy levels, emitting light of specific colors. Each element emits a color unique to the transition of its electrons. Some common flame colors are:

• Lilac: Characteristic of potassium.
• Green: Often associated with copper.
• Yellow: Indicative of sodium.
• Red: Calcium and strontium can emit this color.

Flame tests are just one of many chemical identification methods. Others include spectroscopy, chromatography, and chemical reactivity tests. However, for quick and straightforward detection, flame tests remain a favorite in educational laboratories due to their simplicity and visual appeal. In practice, this technique helps in confirming the identity of elements with minimal equipment and is a staple in teaching the basics of chemical analysis.