Question

Which of the following represents marble? (1) \(\mathrm{CaSO}_{4}\) (2) \(\mathrm{CaCO}_{3}\) (3) \(\mathrm{CaCl}_{2}\) (4) \(\mathrm{MgSO}_{4}\)

Short answer

(2) \(\text{CaCO}_{3}\)

Step-by-step solution

- Identify the Chemical Formula for Marble

Marble is composed mainly of the mineral calcite, which is chemically known as calcium carbonate. The chemical formula for calcium carbonate is \(\text{CaCO}_{3}\).

- Compare Options with Marble's Formula

Examine each given chemical formula to determine whether it matches \(\text{CaCO}_{3}\).

- Find the Matching Formula

Option (2) \(\text{CaCO}_{3}\) matches the chemical formula for marble, while the other options \(\text{CaSO}_{4}\), \(\text{CaCl}_{2}\), and \(\text{MgSO}_{4}\) do not.

Key concepts

calcium carbonate

Calcium carbonate, a chemical compound with the formula \(\text{CaCO}_{3}\), is a widely used substance in both natural and industrial contexts. It appears in several forms, most notably as the minerals calcite and aragonite. This compound is a significant component of rocks like limestone and marble. It is essential in various applications such as manufacturing cement, producing lime, and even in the food industry where it serves as a dietary calcium supplement.

The structure of calcium carbonate consists of calcium ions \(\text{Ca}^{2+}\) and carbonate ions \(\text{CO}_{3}^{2-}\). These ions are held together by ionic bonds.

Common uses of calcium carbonate include:

• Antacid in medicine to neutralize stomach acid
• Filler in plastics and paper products
• Raw material in the production of lime (calcium oxide)

marble composition

Marble is a metamorphic rock that forms when limestone is subjected to significant heat and pressure within the Earth's crust. This natural transformation alters the crystal structure of the mineral grains, making marble distinct from its sedimentary precursor, limestone. The primary mineral in marble is calcite, which as mentioned earlier, is chemically known as calcium carbonate \(\text{CaCO}_{3}\).

The colorful veins seen in marble result from impurities such as iron oxides, silt, and clay present in the original limestone. These impurities can cause various colors like red, green, or black patterns within the predominantly white or gray marble.

Marble is prized for its aesthetic appeal and is commonly used in:

• Building materials and construction (e.g., marble tiles and countertops)
• Sculpture and fine art
• Decorative elements in architecture, such as columns and facades

chemical identification

Chemical identification is a crucial process in determining the specific components and compounds that make up a substance. When identifying a chemical like calcium carbonate, its unique chemical formula \(\text{CaCO}_{3}\) is essential. This process often involves analyzing the substance's physical and chemical properties.

Several methods are used for chemical identification, including:

• **Spectroscopy:** Techniques like infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy identify molecular structures.
• **X-ray diffraction:** This method helps determine crystal structures, useful for minerals.
• **Chemical reactions:** Simple tests can identify compounds based on their reactivity, like adding acid to a carbonate to see if it produces carbon dioxide gas.

Understanding the chemical identity of a material like marble is essential for practical applications and ensuring quality and authenticity in construction and manufacturing industries.