Question

The oxidation number of phosphorus in \(\mathrm{Ba}\left(\mathrm{H}_{2} \mathrm{PO}_{2}\right)_{2}\) is : (a) \(-1\) (b) \(+1\) (c) \(+2\) (d) \(+3\)

Short answer

+1

Step-by-step solution

Understand the Concept of Oxidation Numbers

Oxidation numbers (or states) are theoretical charges that an atom would have if all bonds to atoms of different elements were completely ionic. The sum of oxidation numbers in a neutral compound is zero. Group 1 elements typically have an oxidation state of +1, hydrogen in most of its compounds has an oxidation state of +1, barium as an alkaline earth metal usually has an oxidation state of +2, and oxygen typically has an oxidation state of -2.

Assign Oxidation Numbers to Known Atoms

Barium (Ba) is an alkaline earth metal and thus has an oxidation state of +2. Oxygen (O) usually has an oxidation number of -2. Since hydrogen (H) is not a metal and it's combined with non-metals, its oxidation number is +1.

Write the Formula for Oxidation Number Summation

For the compound \(\mathrm{Ba}\left(\mathrm{H}_{2}\mathrm{PO}_{2}\right)_{2}\), let the oxidation number of phosphorus be x. The compound is neutral, so the sum of oxidation numbers is zero: \[1 \cdot (+2) + 2 \cdot (2 \cdot (+1) + 1 \cdot x + 2 \cdot (-2)) = 0\]

Solve for the Oxidation Number of Phosphorus

Now, solve the equation for x (oxidation number of phosphorus): \[(+2) + 2 \cdot (2 \cdot (+1) + x + 2 \cdot (-2)) = 0\] \[2 + 2 \cdot (2 + x - 4) = 0\] \[2 + 2 \cdot (x - 2) = 0\] \[2 + 2x - 4 = 0\] \[2x - 2 = 0\] \[2x = 2\] \[x = 1\]

Key concepts

Chemical Bonding

Chemical bonding refers to the force that holds atoms together in compounds. Atoms bond by either sharing electrons to form covalent bonds or transferring electrons to form ionic bonds. Understanding the type of bond between atoms is crucial for determining the oxidation states of elements within a molecule. In our example with barium hypophosphite ewlineewlineewlineas an alkaline earth metal typically forms ionic bonds due to its tendency to lose electrons and acquire a +2 oxidation state. On the other hand, phosphorus, hydrogen, and oxygen can form covalent bonds where electrons are shared, influencing their oxidation numbers in complex ways depending on the molecular structure.

Redox Reactions

Redox reactions are chemical processes that involve the transfer of electrons between two species. Reduction describes the gain of electrons, leading to a decrease in oxidation number, whereas oxidation involves the loss of electrons, resulting in an increase in oxidation number. These reactions are fundamental in energy transfer processes, such as in batteries and living organisms' metabolic pathways. Understanding oxidation states is imperative for identifying which atoms are oxidized and which are reduced during these reactions. Even in the case of our compound ewlineewlineewlineexhibiting no net redox process, the concept of oxidation states can still be applied to deduce the formal charge on individual atoms.

Assigning Oxidation States

Assigning oxidation states to elements in a compound involves a set of rules. For example, the oxidation state of pure elements is always zero, and for simple ions, it is equal to the charge of the ion. In molecules, elements like hydrogen and oxygen typically have oxidation numbers of +1 and -2, respectively, unless bonded to more electronegative elements or in peroxides and hydrides. Calculating these oxidation states correctly is essential in understanding the overall charge balance within a molecule. Using the provided formula, we assign values ewlineewlineewlinefor the atoms with known oxidation numbers and then solve for the unknown, such as in the case of phosphorus within barium hypophosphite.

IUPAC Nomenclature

IUPAC nomenclature provides a systematic way to name chemical compounds based on their structure and composition. This standardized protocol enables clear communication among scientists. For instance, barium hypophosphite, the compound in our exercise, can be systematically named based on the oxidation state of phosphorus and the structural features of the compound. Understanding these naming conventions allows for easy recognition and categorization of compounds as well as inferring potential chemical reactions they may undergo. Our equation ewlineewlineewlinehighlights how the oxidation state plays a role not just in understanding chemical reactivity but also in the correct naming of compounds.