Problem 69 - 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, (f) germanium dioxide.

Step-by-Step Solution

Answer

The chemical formulas and oxidation states for the given compounds are: (a) Boric acid: H3BO3, with boron in +3 oxidation state (b) Silicon tetrabromide: SiBr4, with silicon in +4 oxidation state (c) Lead(II) chloride: PbCl2, with lead in +2 oxidation state (d) Sodium tetraborate decahydrate (Borax): Na2B4O7·10H2O, with boron in +3 oxidation state (e) Boric oxide: B2O3, with boron in +3 oxidation state (f) Germanium dioxide: GeO2, with germanium in +4 oxidation state

Step 1: (a) Boric Acid

For boric acid, first we need to know the elements present in it. Boric acid contains boron (B), hydrogen (H), and oxygen (O). The chemical formula for boric acid is H3BO3. Now, we need to determine the oxidation state of boron in this compound. Let the oxidation state of boron be x. For a neutral compound, the sum of the oxidation states of all elements must be equal to zero. We can use the following equation to find the oxidation state of boron: \(x + 3(+1) +3(-2) = 0\) \(x+ 3 - 6 = 0\) \(x = \)3 The oxidation state of boron in boric acid is +3.

Step 2: (b) Silicon Tetrabromide

Silicon tetrabromide contains silicon (Si) and bromine (Br). The chemical formula for silicon tetrabromide is SiBr4. In this compound, the oxidation state of silicon will be: Let the oxidation state of silicon be x. \(x + 4(-1) = 0\) \(x - 4 = 0\) \(x = \)4 The oxidation state of silicon in silicon tetrabromide is +4.

Step 3: (c) Lead(II) Chloride

Lead(II) chloride contains lead (Pb) and chlorine (Cl). The chemical formula for lead(II) chloride is PbCl2. Since it is lead(II), it means that the oxidation state of lead in this compound is +2.

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

Sodium tetraborate decahydrate (borax) contains sodium (Na), boron (B), oxygen (O), and water molecules (H2O). The chemical formula for sodium tetraborate decahydrate is Na2B4O7·10H2O. Now, we need to determine the oxidation state of boron in this compound. Let the oxidation state of boron be x. \(2(+1) + 4x + 7(-2) = 0\) \(2 + 4x - 14 = 0\) \(4x = 12\) \(x = \)3 The oxidation state of boron in sodium tetraborate decahydrate (borax) is +3.

Step 5: (e) Boric Oxide

Boric oxide contains boron (B) and oxygen (O). The chemical formula for boric oxide is B2O3. Now, we need to determine the oxidation state of boron in this compound. Let the oxidation state of boron be x. \(2x + 3(-2) = 0\) \(2x - 6 = 0\) \(x = \)3 The oxidation state of boron in boric oxide is +3.

Step 6: (f) Germanium Dioxide

Germanium dioxide contains germanium (Ge) and oxygen (O). The chemical formula for germanium dioxide is GeO2. Let the oxidation state of germanium be x. \(x + 2(-2) = 0\) \(x - 4 = 0\) \(x = \)4 The oxidation state of germanium in germanium dioxide is +4.

Key Concepts

Chemical Formula

A chemical formula represents the composition of a chemical compound using symbols for its constituent elements and numerical subscripts indicating the number of atoms involved. This concise representation provides essential information about the types and numbers of atoms or ions in a compound.

Understanding a chemical formula is vital for determining the properties and behavior of a substance. For example:

• Water, with the formula \(H_2O\), indicates two hydrogen atoms bonded to one oxygen atom.
• Carbon dioxide, represented as \(CO_2\), consists of one carbon atom double-bonded to two oxygen atoms.

These formulas help predict the outcomes of chemical reactions, understanding molecular structures, and calculating the amount of substances needed in a chemical reaction.

Boric Acid

Boric Acid, known chemically as \(H_3BO_3\), is a weak acid made of boron, hydrogen, and oxygen. It's a common compound used as an antiseptic and insecticide.

The chemical formula \(H_3BO_3\) tells us about the composition of boric acid:

• It has three hydrogen (H) atoms.
• One boron (B) atom.
• Three oxygen (O) atoms.

In boric acid, the oxidation state of boron can be calculated as +3. This is derived by balancing the oxidation numbers to zero, considering hydrogen's +1 and oxygen's -2 states.

The combination of these elements in the specific ratio is what gives boric acid its unique properties and uses.

Silicon Tetrabromide

Silicon tetrabromide, with the chemical formula \(SiBr_4\), is a compound consisting of silicon and bromine. It is often used in the synthesis of other silicon-containing compounds.

In the formula \(SiBr_4\):

• One silicon (Si) atom is centrally bonded to four bromine (Br) atoms.

The oxidation state of silicon in this compound is +4. This can be calculated by knowing that each bromine, being a halogen, usually has an oxidation state of -1. Thus, \(Si + 4(-1) = 0\) simplifies to \(Si = +4\).

Silicon tetrabromide's structure and properties are largely influenced by this oxidation state, affecting its reactivity and application.

Lead(II) Chloride

Lead(II) chloride, denoted by \(PbCl_2\), is a common compound used in optics and ceramics.

The formula \(PbCl_2\) implies:

• One lead (Pb) atom.
• Two chlorine (Cl) atoms.

The Roman numeral "II" indicates that lead has an oxidation state of +2 in this compound. Chlorine generally has an oxidation state of -1. Therefore, the lead atom balances the charges by being +2, leading to a neutral compound. This balancing of charges reflects the stability and the predictable nature of the compound's structure and use in various industrial applications.