Question

Write a molecular formula for each compound, and indicate the oxidation state of the group \(5 \mathrm{~A}\) element in each formula: (a) phosphorous acid, (b) pyrophosphoric acid, (c) antimony trichloride, (d) magnesium arsenide, (e) diphosphorus pentoxide.

Short answer

The molecular formulas and oxidation states of the group 5A elements in the given compounds are as follows: (a) Phosphorous acid: H3PO3, oxidation state of P is \(+3\). (b) Pyrophosphoric acid: H4P2O7, oxidation state of P is \(+5\). (c) Antimony trichloride: SbCl3, oxidation state of Sb is \(+3\). (d) Magnesium arsenide: Mg3As2, oxidation state of As is \(-3\). (e) Diphosphorus pentoxide: P4O10, oxidation state of P is \(+5\).

Step-by-step solution

Identify the chemical symbols

Phosphorous acid consists of phosphorus (P), hydrogen (H), and oxygen (O).

Write the molecular formula

The molecular formula for phosphorous acid is H3PO3.

Determine the oxidation state of phosphorus

Let the oxidation state of phosphorus be x. We have: x + 3(+1) + 3(-2) = 0 (since the total charge in a neutral molecule is zero) x = +3 The oxidation state of phosphorus in phosphorous acid is \(+3\). #b) Pyrophosphoric Acid#

Identify the chemical symbols

Pyrophosphoric acid consists of phosphorus (P), hydrogen (H), and oxygen (O).

Write the molecular formula

The molecular formula for pyrophosphoric acid is H4P2O7.

Determine the oxidation state of phosphorus

Let the oxidation state of phosphorus be x. In this case, we have 2 phosphorus atoms, so 2x will denote the total oxidation state of phosphorus in the molecule. We have: 2x + 4(+1) + 7(-2) = 0 x = +5 The oxidation state of phosphorus in pyrophosphoric acid is \(+5\). #c) Antimony Trichloride#

Identify the chemical symbols

Antimony trichloride consists of antimony (Sb) and chlorine (Cl).

Write the molecular formula

The molecular formula for antimony trichloride is SbCl3.

Determine the oxidation state of antimony

Let the oxidation state of antimony be x. We have: x + 3(-1) = 0 x = +3 The oxidation state of antimony in antimony trichloride is \(+3\). #d) Magnesium Arsenide#

Identify the chemical symbols

Magnesium arsenide consists of magnesium (Mg) and arsenic (As).

Write the molecular formula

The molecular formula for magnesium arsenide is Mg3As2.

Determine the oxidation state of arsenic

Let the oxidation state of arsenic be x. In this case, we have 2 arsenic atoms, so 2x will denote the total oxidation state of arsenic in the molecule. We have: 3(+2) + 2x = 0 x = -3 The oxidation state of arsenic in magnesium arsenide is \(-3\). #e) Diphosphorus Pentoxide#

Identify the chemical symbols

Diphosphorus pentoxide consists of phosphorus (P) and oxygen (O).

Write the molecular formula

The molecular formula for diphosphorus pentoxide is P4O10.

Determine the oxidation state of phosphorus

Let the oxidation state of phosphorus be x. In this case, we have 4 phosphorus atoms, so 4x will denote the total oxidation state of phosphorus in the molecule. We have: 4x + 10(-2) = 0 x = +5 The oxidation state of phosphorus in diphosphorus pentoxide is \(+5\).

Key concepts

Oxidation State

The term **oxidation state** refers to the total number of electrons an atom either gains or loses to form a chemical bond. It's a crucial concept in chemistry because it helps us understand how elements interact in compounds. In a neutral molecule, the sum of the oxidation states always equals zero. This rule allows chemists to determine the oxidation state of individual elements within a compound by setting up an equation where the sum of all oxidation states equals zero.
For instance, in phosphorous acid (H3PO3), the oxidation state of hydrogen (H) is typically +1, and oxygen (O) is -2. If you assume phosphorus (P) has an unknown oxidation state "x", you can set up the equation:

• For phosphorous acid: \( x + (3 imes +1) + (3 imes -2) = 0 \)
  Solving this gives us \( x = +3 \).
• This methodology helps us deduce that phosphorus in phosphorous acid has an oxidation state of +3.

Group 5A Elements

Elements classified as **Group 5A elements** include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). These elements are located in the 15th column of the periodic table and are typically characterized by having five electrons in their outermost energy levels.
Group 5A elements display varying oxidation states, often ranging from -3 to +5. This variability is due to their electron configuration and ability to form multiple bonds:

• Phosphorus often exhibits oxidation states of +3, +5, and -3, which are especially important in biological systems and various inorganic compounds.
• Arsenic commonly shows oxidation states of -3, +3, and +5 and is known for its use in semiconductors.
• Antimony typically displays oxidation states of +3 and +5 in compounds.

These concepts are critical in predicting compound formation and properties.

Chemical Symbols

**Chemical symbols** are shorthand notations that represent chemical elements. They are one or two-letter abbreviations derived from the element's name, often Latin or Greek origins, allowing chemists to communicate formulas succinctly.
Using chemical symbols in formulas helps identify the composition and proportions of elements in chemical compounds:

• "P" for phosphorus.
• "O" for oxygen.
• "H" for hydrogen.
• "Sb" for antimony.
• "Cl" for chlorine.
• "Mg" for magnesium.
• "As" for arsenic.

These symbols form the basis of writing chemical equations and understanding compound interactions.

Phosphorus Compounds

**Phosphorus compounds** are crucial in both biological systems and industrial applications. Phosphorus forms a variety of compounds, which take different roles based on their oxidation states and molecular structures.
Key phosphorus compounds include:

• Phosphorous acid (H3PO3): Used in chemical industries and agriculture; features phosphorus with an oxidation state of +3.
• Pyrophosphoric acid (H4P2O7): Found in biochemistry as a potential intermediate in the formation of high-energy bonds; carrying phosphorus with an oxidation state of +5.
• Diphosphorus pentoxide (P4O10): Utilized as a powerful dehydrating agent, showcasing phosphorus with an oxidation state of +5.

These compounds highlight phosphorus's versatility by exhibiting different chemical properties and reactions based on their structures and oxidation states.