Problem 163 - A Complete Resource Book in Chemistry for JEE Main

Question

\text { Among the following minerals, siderite, malachite, }cerussite, anglessite, smithsonite, diaspore, mica and corundum, the number of carbonate minerals is

Step-by-Step Solution

Answer

There are four carbonate minerals.

Step 1: Identify Carbonate Minerals

Carbonate minerals are those that contain carbonate groups, which have the chemical formula \(CO_3^{2-}\). Our task is to identify which of the given minerals are carbonate minerals: siderite, malachite, cerussite, anglessite, smithsonite, diaspore, mica, and corundum.

Step 2: Analyze Each Mineral

- **Siderite**: The chemical formula is \(FeCO_3\), which contains the \(CO_3^{2-}\) group. Thus, it is a carbonate mineral.- **Malachite**: The chemical formula is \(Cu_2CO_3(OH)_2\). This contains the carbonate group, so it is a carbonate mineral.- **Cerussite**: The chemical formula is \(PbCO_3\), containing the \(CO_3^{2-}\) group, making it a carbonate mineral.- **Anglessite**: The chemical formula is \(PbSO_4\), which contains sulfate, not carbonate.- **Smithsonite**: The chemical formula is \(ZnCO_3\), which includes the \(CO_3^{2-}\) group. Therefore, it is a carbonate mineral.- **Diaspore**: The chemical formula is \(AlO(OH)\), which does not contain \(CO_3^{2-}\), so it is not a carbonate mineral.- **Mica**: Mica group minerals do not have carbonates in their structure.- **Corundum**: The chemical formula is \(Al_2O_3\), which lacks the \(CO_3^{2-}\) group.

Step 3: Count Carbonate Minerals

From the analysis, the carbonate minerals identified are: siderite, malachite, cerussite, and smithsonite. Count these minerals to determine the number of carbonate minerals.

Key Concepts

Chemical Formulas

Every mineral has a unique composition that is represented by a chemical formula. This formula provides key insights into the elements that make up the mineral. For example, the formula for cerussite is \(PbCO_3\), which reveals that it contains lead \(Pb\) and the carbonate group \(CO_3^{2-}\).
Understanding chemical formulas is crucial for identifying specific mineral groups. Formulas typically show the types and amounts of each atom in the mineral. For instance, a formula like \(FeCO_3\) for siderite shows it includes iron \(Fe\) and the carbonate group. Knowing these formulas makes it easier to classify minerals into groups such as carbonates, silicates, or sulfides.
When examining minerals, the primary focus is often on the anion or anionic group, such as \(CO_3^{2-}\) in carbonates. This helps determine the classification of the mineral, since minerals are primarily classified by their dominant anions.

Mineral Classification

Mineral classification organizes minerals into groups based on their chemical composition and structure. It helps geologists and gemologists understand the properties and formation of minerals. The primary basis for classification is the dominant anion or anionic group in the mineral's structure.

• **Carbonates:** These minerals contain the carbonate group \(CO_3^{2-}\). Examples include calcite \(CaCO_3\) and siderite \(FeCO_3\).
• **Sulfates:** Minerals like gypsum \(CaSO_4 \, 2H_2O\), featuring the sulfate group \(SO_4^{2-}\).
• **Silicates:** The most abundant group, characterized by the silicate group \(SiO_4^{4-}\), often forming complex structures.

The classification is essential not only for identification but also for practical purposes such as mining and material use. Each group has distinct physical and chemical properties, making classification vital for applications ranging from industrial to jewelry making.

Carbonate Group Identification

Identifying carbonate minerals revolves around detecting the \(CO_3^{2-}\) anion in their chemical formula. This group is vital for determining if a mineral belongs to the carbonate family.
Carbonates are widespread in the Earth's crust and often found in sedimentary rocks. Common carbonate minerals include calcite, dolomite, and aragonite, all renowned for their reactivity with acids. They effervesce when exposed to diluted hydrochloric acid due to the release of \(CO_2\) gas.
To identify carbonate minerals, check if the chemical formula includes \(CO_3^{2-}\). For example:

• **Siderite**: \(FeCO_3\)
• **Malahite**: \(Cu_2CO_3(OH)_2\)
• **Cerussite**: \(PbCO_3\)
• **Smithsonite**: \(ZnCO_3\)

Minerals without a carbonate group, like diaspore \(AlO(OH)\), are not considered carbonates. Recognizing this group is fundamental for students, enabling them to accurately classify minerals and understand their basic compositions.