Question

Name the chemical compound(s) you would expect to be the primary constituent(s) of (a) stalactites; (b) gypsum; (c) "barium milkshake"; (d) blue sapphires.

Short answer

The primary constituents of the substances are: (a) Stalactites - Calcium Carbonate (CaCO3), (b) Gypsum - Calcium Sulfate Dihydrate (CaSO4·2H2O), (c) 'Barium Milkshake' - Barium Sulfate (BaSO4), (d) Blue Sapphires - Aluminum Oxide (Al2O3).

Step-by-step solution

Identification of the Primary Constituent of Stalactites

Stalactite is a type of formation found in caves, formed by the deposition of minerals from water dripping from the cave's roof. The primary constituent of stalactites is Calcium Carbonate (CaCO3) in the form of calcite.

Identification of the Primary Constituent of Gypsum

Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate. Its chemical formula is CaSO4·2H2O.

Identification of the Primary Constituent of 'Barium Milkshake'

'Barium Milkshake' is a common term used in healthcare settings to describe a barium meal or solution consumed to enhance the visibility of the intestinal tract in X-ray diagnostics. The primary constituent of a 'Barium Milkshake' is Barium Sulfate (BaSO4).

Identification of the Primary Constituent of Blue Sapphires

Sapphire is a variety of the mineral corundum, essentially composed of aluminium oxide with impurities determining its color. Blue sapphire gets its color primarily from the presence of iron and titanium impurities. So the primary constituent of sapphires is Aluminum Oxide (Al2O3).

Key concepts

Calcium Carbonate (CaCO3)

Calcium carbonate, known by its formula CaCO3, is not only a significant component of stalactites but also a key material in various applications, including construction, as the primary ingredient in cement and as a substance used for neutralizing acidic soil. When it comes to stalactites, these fascinating formations hang like icicles within caves and are a testament to the slow and steady process of mineral deposition. The calcium carbonate is deposited as the mineral calcite from dripping water that is supersaturated with calcium bicarbonate. Over time, the evaporation of water leaves behind the calcium carbonate, allowing the stalactite to grow.

This versatile compound also appears in other natural forms such as limestone and marble, forming through biomineralization processes or even by direct precipitation from water. Because of its widespread presence in the earth's crust, it plays a critical role in the carbon cycle as well.

Gypsum (CaSO4·2H2O)

Gypsum, or calcium sulfate dihydrate, is a soft mineral with the chemical formula CaSO4·2H2O, illustrating that two water molecules are included in its crystalline structure. Its readiness to form as evaporite deposits makes it common in sedimentary environments. Gypsum's use extends into industries like agriculture as a soil conditioner, but it's also essential in construction as the main ingredient in drywall or plaster. It possesses properties that make it easy to shape and sculpt when mixed with water, yet it hardens into a durable and fire-resistant material.

One of gypsum's unique features is its ability to hold onto water, which helps to regulate quality when used as a land amendment. Moreover, in its purest form, gypsum can be transparent, but it's typically found in white or slightly colored varieties due to impurities like other chemical elements or organic materials.

Barium Sulfate (BaSO4)

Barium Sulfate, with its chemical formula BaSO4, is a mineral known as barite in its natural state, but perhaps more famously referred to as the key ingredient in the so-called 'Barium Milkshakes' used in medical imaging. Its high density and radio-opaque nature make it perfect for providing contrast in X-ray imaging, notably for examining the gastrointestinal tract. Although comparing a medical compound to a milkshake might seem whimsical, it emphasizes the need for the patient to ingest the substance.

Barium sulfate is virtually insoluble in water, which makes it safe for such procedures as it doesn't dissolve and get absorbed into the bloodstream. Additionally, the compound is used industrially in paint, as a filler in plastics, and in oil drilling fluids, exploiting its characteristic density and inertness.

Aluminum Oxide (Al2O3)

Aluminum oxide, also known as alumina with the formula Al2O3, is a hard and durable material found predominantly in bauxite ore, which is the primary source of aluminum metal. However, what might be most captivating is its role in forming gemstones such as sapphires and rubies; the impurities within its crystalline structure define their coloring. Blue sapphires owe their deep, rich color to the presence of iron and titanium.

Aside from its gemstone celebrity, aluminum oxide is also incredibly useful in a range of applications, including as an abrasive, in the manufacture of refractory materials, and as a component of cutting tools. It's known for its superior thermal stability, which allows it to withstand high temperatures without decomposing, making it integral in industrial processes that require materials with high melting points.