Problem 75 - Chemistry: The Central Science

Question

Write the formulas for the following compounds, and indicate the oxidation state of the group 4 A element or of boron in each: (a) boric acid, (b) silicon tetrabromide, (c) lead(II) chloride, (d) sodium tetraborate decahydrate (borax), (e) boric oxide.

Step-by-Step Solution

Answer

The chemical formulas and oxidation states for the given compounds are (a) boric acid: H3BO3, boron oxidation state +3; (b) silicon tetrabromide: SiBr4, silicon oxidation state +4; (c) lead(II) chloride: PbCl2, lead oxidation state +2; (d) sodium tetraborate decahydrate (borax): Na2B4O7·10H2O, boron oxidation state +3; (e) boric oxide: B2O3, boron oxidation state +3.

Step 1: (a) Boric Acid Formula

Boric acid is H3BO3. It contains three hydrogen atoms (H), one boron atom (B), and three oxygen atoms (O). The oxidation state of boron in boric acid is +3.

Step 2: (b) Silicon Tetrabromide Formula

Silicon tetrabromide is SiBr4. It contains one silicon atom (Si) and four bromine atoms (Br). The oxidation state of silicon in silicon tetrabromide is +4, as each bromine atom has an oxidation state of -1, and the overall charge of the molecule is neutral.

Step 3: (c) Lead(II) Chloride Formula

Lead(II) chloride is PbCl2. It contains one lead atom (Pb) and two chlorine atoms (Cl). The oxidation state of lead in lead(II) chloride is +2, which is indicated by the Roman numeral in the name of the compound.

Step 4: (d) Sodium Tetraborate Decahydrate (Borax) Formula

Sodium tetraborate decahydrate (borax) is Na2B4O7·10H2O. It contains two sodium atoms (Na), four boron atoms (B), seven oxygen atoms (O), and twenty hydrogen atoms (H) in the form of water of hydration (10H2O). The oxidation state of boron in sodium tetraborate is +3, as in boric acid.

Step 5: (e) Boric Oxide Formula

Boric oxide is B2O3. It contains two boron atoms (B) and three oxygen atoms (O). The oxidation state of boron in boric oxide is +3, as in boric acid and sodium tetraborate.

Key Concepts

Boric Acid Formula

Boric acid, chemically represented as \( H_3BO_3 \), is a simple compound consisting of three hydrogen atoms, one boron atom, and three oxygen atoms. Boron exhibits an oxidation state of +3 in this compound, which is typical for boron-containing compounds. This simple acid is often used as an antiseptic, insecticide, or in various industrial processes. Here, each hydrogen atom has an oxidation state of +1, and each oxygen atom has a -2 oxidation state.

• Formula: \( H_3BO_3 \)
• Oxidation State of Boron: +3
• Uses include antiseptics and insecticides

Silicon Tetrabromide

Silicon tetrabromide, denoted as \( SiBr_4 \), consists of one silicon atom combined with four bromine atoms. In this molecule, silicon takes on an oxidation state of +4, due to each bromine atom having a -1 oxidation state. This compound is an example of a tetrahalide, where a single central atom (silicon) is bonded to four halogen atoms.

• Formula: \( SiBr_4 \)
• Oxidation State of Silicon: +4
• Features tetrahaploid structure

Lead(II) Chloride

Lead(II) chloride, symbolized as \( PbCl_2 \), includes one lead atom joined to two chlorine atoms. The Roman numeral (II) indicates that lead's oxidation state is +2. Chlorine atoms each have an oxidation state of -1, balancing the overall charge of the compound. This particular chloride is known for its use in pigment production, as well as in industrial applications.

• Formula: \( PbCl_2 \)
• Oxidation State of Lead: +2
• Applications in pigments and industrial processes

Sodium Tetraborate Decahydrate

Sodium tetraborate decahydrate, more commonly referred to as borax, is a compound with the formula \( Na_2B_4O_7 \, \cdot \, 10H_2O \). This complex molecule includes two sodium atoms, four boron atoms, seven oxygen atoms, and ten additional water molecules. Boron within this compound retains an oxidation state of +3, as found in boric acid. Borax has widespread applications, notably in laundry cleaning, water softening, and as a buffering agent in chemical laboratories.

• Formula: \( Na_2B_4O_7 \, \cdot \, 10H_2O \)
• Oxidation State of Boron: +3
• Popular in cleaning and chemical applications

Boric Oxide

Boric oxide, known chemically as \( B_2O_3 \), is formed from two boron atoms paired with three oxygen atoms. It shares the +3 oxidation state for boron as seen in both boric acid and sodium tetraborate. This oxide is fundamentally crucial in the creation of borosilicate glass, and it serves as a flux in metallurgy and ceramics.

• Formula: \( B_2O_3 \)
• Oxidation State of Boron: +3
• Central in glassmaking and metallurgy