Problem 124 - Chemistry Matter and Change

Question

Write the formula for each molecule. a. chlorine monoxide b. arsenic acid c. phosphorus pentachloride d. hydrosulfuric acid

Step-by-Step Solution

Answer

a. \(ClO\) b. \(H_3AsO_4\) c. \(PCl_5\) d. \(H_2S\)

Step 1: a. Chlorine Monoxide

Here, we have two elements - Chlorine (Cl) and Oxygen (O). Chlorine has a valence of 1 (it wants to gain one electron) and Oxygen has a valence of 2 (it wants to gain two electrons). Since it's a 1 to 1 ratio (monoxide), the chemical formula is simply \(ClO\).

Step 2: b. Arsenic Acid

Arsenic acid contains Arsenic (As) and a hydroxide ion (OH) with a charge of -1. Arsenic forms a +5 valence state in arsenic acid. We need to balance the charges to get the correct chemical formula. Since we have 5 positive charges from Arsenic and 1 negative charge from each hydroxide ion, we will need 5 hydroxide ions to balance the charges. The chemical formula for arsenic acid is \(H_3AsO_4\).

Step 3: c. Phosphorus Pentachloride

In this molecule, we have Phosphorus (P) and Chlorine (Cl). Phosphorus has a valence of 5 (wants 5 more electrons) and Chlorine has a valence of 1 (wants 1 more electron). To maintain the proper balance between these elements, we need 5 Chlorine atoms for each Phosphorus atom. Thus, the correct chemical formula for phosphorus pentachloride is \(PCl_5\).

Step 4: d. Hydrosulfuric Acid

Hydrosulfuric acid contains Hydrogen (H) with a valence of 1 (wants 1 more electron) and Sulfur (S) with a valence of 2 (wants 2 more electrons). Since both have a 1:2 ratio, we need two hydrogen atoms for each sulfur atom to create a balanced molecule. The chemical formula for hydrosulfuric acid is \(H_2S\).

Key Concepts

Chlorine Monoxide

Chlorine Monoxide is a molecule composed of one chlorine atom and one oxygen atom. It is often represented chemically as \( ClO \). In forming this compound, the valence states of the elements play a crucial role.

• Chlorine (Cl): Chlorine aims to gain one electron to achieve a stable electron configuration.
• Oxygen (O): Oxygen wants to gain two electrons for stability.

Because this compound is termed "monoxide," it indicates that there is only one oxygen atom. The simplicity of the formula \( ClO \) lies in the direct 1:1 ratio of both chlorine and oxygen in the molecule.

Arsenic Acid

Arsenic acid is a more complex molecule often used in industrial processes. It consists of arsenic and hydroxide groups. Its formula \( H_3AsO_4 \) gives insights into its composition and balance.

• Arsenic (As): In arsenic acid, arsenic usually exhibits a +5 oxidation state, which means it can combine with five negative charges.
• Hydroxide Group (OH): Each hydroxide ion carries a -1 charge.

To balance the +5 charge from arsenic, the molecule contains three hydrogen atoms, one arsenic atom, and four oxygen atoms. This configuration ensures that the charge is balanced, yielding a stable molecule often involved in chemical reactions.

Phosphorus Pentachloride

Phosphorus Pentachloride is an essential compound in chemistry used in various synthesis processes. The formula \( PCl_5 \) showcases its composition.

• Phosphorus (P): Exhibiting a valence of +5 means it can accept five chloride ions.
• Chlorine (Cl): Each chlorine acts as a single negatively charged ion.

The name "pentachloride" indicates the presence of five chlorine atoms. This leads to a clear understanding that for every phosphorus atom, five chlorine atoms are needed. Thus, \( PCl_5 \) forms a highly reactive compound often used in manufacturing and chemical industries.

Hydrosulfuric Acid

Hydrosulfuric acid, known by the chemical formula \( H_2S \), is a simple yet vital compound in both nature and industry. The composition is due to sulfur and hydrogen's valence requirements.

• Hydrogen (H): Each hydrogen atom wants to gain one electron.
• Sulfur (S): Sulfur has a tendency to gain two electrons for a stable configuration.

In hydrosulfuric acid, the 2-to-1 hydrogen to sulfur ratio ensures complete satisfaction of sulfur's electron appetite. \( H_2S \) is frequently encountered as a gas with a distinctive smell, reminiscent of rotten eggs, and plays significant roles in various chemical processes.