Problem 76 - Chemistry The Central Science

Question

(a) Determine the number of sodium ions in the chemical formula of albite, \(\mathrm{Na}_{x} \mathrm{AlSi}_{3} \mathrm{O}_{8}\) . (b) Determine the number of hydroxide ions in the chemical formula of tremolite, \(\mathrm{Ca}_{2} \mathrm{Mg}_{5}\left(\mathrm{Si}_{4} \mathrm{O}_{11}\right)_{2}(\mathrm{OH})_{x}\)

Step-by-Step Solution

Answer

(a) The number of sodium ions in the chemical formula of albite, \(\mathrm{Na}_{x} \mathrm{AlSi}_{3} \mathrm{O}_{8}\), is 1. (b) The number of hydroxide ions in the chemical formula of tremolite, \(\mathrm{Ca}_{2}\mathrm{Mg}_{5}\left(\mathrm{Si}_{4}\mathrm{O}_{11}\right)_{2}(\mathrm{OH})_{x}\), is 1.

Step 1: Identify the subscript of sodium ions in the chemical formula of albite

The given chemical formula for albite is \(\mathrm{Na}_{x} \mathrm{AlSi}_{3} \mathrm{O}_{8}\). Sodium ions are represented by \(\mathrm{Na}\). According to the formula, the subscript for sodium ions is `x`.

Step 2: Determine the number of sodium ions in the chemical formula of albite

The subscript for sodium ions in the chemical formula of albite is `x`. Since there is no numerical value given, it means there is only 1 sodium ion present in the formula. So we have found that the number of sodium ions in albite is 1.

Step 3: Identify the subscript of hydroxide ions in the chemical formula of tremolite

The given chemical formula for tremolite is \(\mathrm{Ca}_{2}\mathrm{Mg}_{5}\left(\mathrm{Si}_{4}\mathrm{O}_{11}\right)_{2}(\mathrm{OH})_{x}\). Hydroxide ions are represented by \(\mathrm{OH}\). The subscript for hydroxide ions in the formula is `x`.

Step 4: Determine the number of hydroxide ions in the chemical formula of tremolite

The subscript for hydroxide ions in the chemical formula of tremolite is `x`. Since there is no numerical value given, it means there is only one hydroxide ion present in the formula. So we have found that the number of hydroxide ions in tremolite is 1.

Key Concepts

Molecular Subscripts

Molecular subscripts are like little numbers that indicate the quantity of each type of atom in a molecule. These subscripts are essential because they provide crucial information about the composition of a chemical compound. When you see a subscript in a chemical formula, it tells you how many atoms of the element are present. For example, in water (H₂O), the subscript "2" tells us there are two hydrogen atoms for every oxygen atom in a molecule of water.
In the case of albite, represented as Na_xAlSi₃O₈, if the subscript for sodium (Na) is not specified, and just shows "x", it often means that in its pure form, only one sodium atom is intended. Consider also tremolite: in the chemical formula Ca₂Mg₅(Si₄O₁₁)₂(OH)_x, "x" in OH is also typically defaulted to 1 unless specified otherwise. Knowing these numbers helps chemists and students alike to calculate the correct proportions and even predict reactions.

Ions in Minerals

Ions are atoms or molecules that have gained or lost electrons, giving them a charge. In the world of minerals, ions combine to form the crystalline structures that give minerals their characteristics. Each mineral has a unique combination of cations (positively charged ions) and anions (negatively charged ions).
In the mineral albite, the presence of sodium ions (Na⁺) is crucial. Sodium ions play a significant role in the aluminosilicate network, binding with other ions to form the stable structure of the mineral. For tremolite, components like calcium (Ca²⁺), magnesium (Mg²⁺), and hydroxide ions (OH^-) determine the physical properties and stability of this mineral. Understanding the role of these ions helps in predicting mineral behavior.

Albite and Tremolite

Albite and tremolite are minerals that are part of larger groups, the feldspar and amphibole families, respectively.

• Albite: This mineral is a sodium-rich feldspar that is a part of the plagioclase feldspar series. Its chemical formula is often seen as NaAlSi₃O₈. It's commonly found in igneous rocks and is a significant component of granite. Its role in geology is crucial as its presence can impact the classification and naming of rock types.
• Tremolite: An amphibole mineral with a typical formula of Ca₂Mg₅(Si₄O₁₁)₂(OH)₂. This mineral is often found in metamorphosed limestone and dolomites. It is part of the significant asbestos family, showcasing fibrous structures that once had industrial applications until the health risks were fully recognized.

Exploring these minerals, we see how chemical formulas reflect their structures, providing insights into their formation and properties. Knowing how to read these formulas helps us understand mineral composition and behavior.