Question

Phosphorus forms many oxoacids. Indicate the oxidation number of phosphorus in each of the following acids: (a) \(\mathrm{HPO}_{3},\) (b) \(\mathrm{H}_{3} \mathrm{PO}_{2},\) (c) \(\mathrm{H}_{3} \mathrm{PO}_{3}\), (d) \(\mathrm{H}_{3} \mathrm{PO}_{4},\) (e) \(\mathrm{H}_{4} \mathrm{P}_{2} \mathrm{O}_{7}\) (f) \(\mathrm{H}_{5} \mathrm{P}_{3} \mathrm{O}_{10}\)

Short answer

The oxidation numbers are: (a) +5, (b) +1, (c) +3, (d) +5, (e) +5, (f) +5.

Step-by-step solution

Understand the oxidation number concept

The oxidation number (also called oxidation state) of an atom is a measure of the degree of oxidation of an atom in a substance. It is an indicator of the loss of electrons compared to the elemental state. Common rules to determine oxidation numbers include: hydrogen is usually +1, oxygen is usually -2, and the sum of oxidation numbers in a neutral compound is zero.

Calculate the oxidation number of P in HPO₃

For \(HPO_3\), hydrogen has an oxidation number of +1, and oxygen has an oxidation number of -2. The equation to find the oxidation number of phosphorus (P) is: \(+1 + x + 3(-2) = 0\). Solving gives \(x = +5\).

Calculate oxidation number of P in H₃PO₂

For \(H_3PO_2\), hydrogen is +1, oxygen is -2. The equation is \(3(+1) + x + 2(-2) = 0\). Solving gives \(x = +1\).

Determine oxidation number of P in H₃PO₃

For \(H_3PO_3\), hydrogen is +1, oxygen is -2. The equation is \(3(+1) + x + 3(-2) = 0\). Solving gives \(x = +3\).

Determine oxidation number of P in H₃PO₄

For \(H_3PO_4\), hydrogen is +1 and oxygen is -2. Solving \(3(+1) + x + 4(-2) = 0\) gives \(x = +5\).

Analyze oxidation number of P in H₄P₂O₇

For \(H_4P_2O_7\), hydrogen is +1, oxygen is -2, and there are two phosphorus atoms. The equation is \(4(+1) + 2x + 7(-2) = 0\), leading to \(2x = +10\), hence \(x = +5\).

Analyze oxidation number of P in H₅P₃O₁₀

In \(H_5P_3O_{10}\), hydrogen has an oxidation state of +1, and oxygen is -2. The equation is \(5(+1) + 3x + 10(-2) = 0\). Solving gives \(3x = +15\), so \(x = +5\).

Key concepts

Phosphorus Oxoacids

Phosphorus is a fascinating element that forms various oxoacids, where phosphorus is bonded to oxygen and hydrogen. These include

• Hypophosphorous acid ( H_3PO_2),
• Phosphorous acid ( H_3PO_3),
• and Phosphoric acid ( H_3PO_4).

Oxoacids of phosphorus are essential in chemistry because of their diverse application in fields such as fertilizers and food industry. These acids have phosphorus in different oxidation states, impacting their chemical reactivity and properties. Understanding their structure is crucial for predicting their behavior in chemical reactions. Phosphorus oxoacids have a central phosphorus atom surrounded by oxygen, and this connectivity defines much of its chemistry. It is important to grasp these structures to comprehend how phosphorus can adapt different oxidation numbers in various compounds.

Oxidation State Calculation

Calculating oxidation states is an essential skill in chemistry. It helps understand how elements interact in a compound. It's a numeral representing an atom's electron control compared to when it is a part of a molecule.The most straightforward rules are:

• Hydrogen is typically +1,
• oxygen is usually −2,
• and the sum of oxidation states in a neutral compound must equal zero.

For example, in the molecule HPO_3, the oxidation number of phosphorus can be calculated by letting it be "x," resulting in the equation: \(+1 + x + 3(-2) = 0\). Solving it gives the oxidation number for phosphorus.These principles are repeated for each compound, ensuring consistency while solving for unknown oxidation numbers.

Chemical Equation Balancing

Balancing chemical equations is all about ensuring that the number of atoms for each element is equal on both sides of the equation. It's a fundamental concept that reflects the conservation of mass principle in chemistry. In oxidation state calculations, balancing allows chemists to ensure the total charge is consistent across reactants and products. When you deal with complex compounds like phosphorus oxoacids, balancing is tricky yet crucial. You need to factor in both the number of atoms and their oxidation states to derive accurate results. This aligns with the need for meticulous calculation, as seen with the determination of phosphorus's oxidation state in various acids. It's a skill that takes practice but is invaluable for understanding chemical interactions.

Redox Chemistry

Redox (reduction-oxidation) reactions are central to many chemical processes, where one substance gains electrons (reduction) while another loses electrons (oxidation). Understanding oxidation numbers is crucial because they allow you to pinpoint which atoms are being oxidized or reduced in reactions. Consider phosphorus oxoacids:

• the phosphoric acid ( H_3PO_4) has phosphorus in a +5 oxidation state,
• while phosphorous acid ( H_3PO_3) has a +3 state.

This difference highlights how phosphorus's different oxidation states can participate in various redox reactions. Recognizing such patterns is crucial for predicting how substances might behave during redox reactions and identifying key chemical processes in different environments. This understanding can also aid in industrial applications such as synthesizing new compounds or developing energy solutions like batteries.