Problem 27 - A Complete Resource Book in Chemistry for JEE Main

Question

Chromite ore can be given as (a) \(\mathrm{FeCr}_{2} \mathrm{O}_{7}\) (b) \(\mathrm{Cr}_{2} \mathrm{O}_{3}\) (c) \(\mathrm{FeCr}_{2} \mathrm{O}_{4}\) (d) \(\mathrm{Fe}_{3} \mathrm{O}_{4}\)

Step-by-Step Solution

Answer

Chromite ore is represented by option (c) \(\mathrm{FeCr}_2 \mathrm{O}_4\).

Step 1: Identify Chromite Ore

The chemical composition of chromite ore is generally represented as ext{FeCr}_2 ext{O}_4. This is known as chromite, where iron (II) and chromium (III) are combined with oxygen.

Step 2: Match Given Options

Examine the given options to find the one that matches ext{FeCr}_2 ext{O}_4. Option (c) is ext{FeCr}_2 ext{O}_4, which is the correct representation of chromite ore.

Step 3: Verify Other Options

Check the other options to confirm that they do not match chromite: \((a) \text{FeCr}_2\text{O}_7\) is incorrect, \((b) \text{Cr}_2\text{O}_3\) is chromium (III) oxide, not chromite, and \((d) \text{Fe}_3\text{O}_4\) is magnetite, another iron oxide, not chromite.

Key Concepts

Chemical Composition

The chemical composition of chromite ore is most commonly represented by the formula \(\mathrm{FeCr}_2 \mathrm{O}_4\). This formula is a critical identifier for the mineral known as chromite, which is an iron chromium oxide. In this compound:

• Fe stands for iron, which exists in a +2 oxidation state.
• Cr is chromium, taking on a +3 oxidation state, an expression of its stable form in this compound.
• O represents oxygen, which typically has a -2 oxidation state.

Together, these elements form a stable lattice structure, balancing charge overall and forming a unique crystal system. Understanding the chemical composition is vital as it determines the mineral's properties and potential uses, especially in industrial processes.

Chromium Compounds

Chromium compounds are diverse and play substantial roles in various chemical processes and industries. The chromium found in chromite (\(\mathrm{FeCr}_2 \mathrm{O}_4\)) is primarily in the +3 oxidation state, which is the most stable and commonly found in nature.Here’s a breakdown of a few key chromium compounds:

• Chromium (III) Oxide \(\mathrm{Cr}_2 \mathrm{O}_3\): This is a green pigment and a compound used in refractory materials. It's important to note that though related, it is not chromite.
• Chromium (VI) Compounds: Unlike the stable +3 state, +6 compounds like chromates and dichromates are more reactive and often utilized in metal plating and as oxidizing agents, though they are less stable.

These variations demonstrate the versatile nature of chromium and explain why chromite is such a valuable source of this metal, linking its chemistry to its applications.

Mineral Identification

Identifying minerals like chromite relies heavily on their unique physical and chemical properties. Chromite, dominated by the \(\mathrm{FeCr}_2\mathrm{O}_4\) formula, is distinguished from other minerals through various techniques.Some methods of identification include:

• Color and Streak: Chromite typically appears with a dark brown to a black color, providing a definitive black streak on unglazed porcelain tiles.
• Density: It has a relatively high density for a mineral, due to its iron content.
• Magnetism: Chromite is weakly magnetic, a feature that helps differentiate it from strongly magnetic minerals like magnetite \(\mathrm{Fe_3O_4}\).

By examining such properties, geologists and chemists can accurately identify and classify chromite among thousands of minerals found on Earth.

Inorganic Chemistry

Inorganic chemistry involves the study of minerals and compounds, such as chromite, outside of organic frameworks. It explores elements and their interactions, particularly metals, which are abundant in the Earth's crust. Chromite's place in inorganic chemistry revolves around:

• Stable Oxidation States: As an oxide of chromium, chromite features a prominently stable chromium (III) due to its full-thickness electron shell configuration.
• Coordination Chemistry: In chromite, chromium ions are surrounded by oxygen ions forming a specific coordination geometry that gives the mineral its physical properties.
• Reactivity: Understanding factors like these helps in predicting the reactivity and possible applications of chromium and chromite in industries ranging from metallurgy to pigment production.

By examining chromite through the lens of inorganic chemistry, we garner insights into its importance and functionality in both natural settings and industrial applications.