Question

What is the oxidation state of phosphorus in $C{a_3}{P_2}$?

Answer 1

We have to know that the oxidation state, sometimes referred to as oxidation number, describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. Conceptually, the oxidation state, which may be positive, negative or zero, is the hypothetical charge of an atom.

Complete answer:
Let x be the oxidation state of phosphorus in respective compounds. Sum of oxidation states of all entities in the compound is equal to its charge.
$3 \times \left( { + 2} \right) + \left( {2 \times x} \right) = {\text{ }}0$
$6 + 2x = 0$
$2x = - 6$
$\Rightarrow x = - 3$
We have to know that the oxidation state can be a total charge on a compound. Calcium phosphide is the inorganic compound with the formula $C{a_3}{P_2}$. It is one of several phosphides of calcium, being described as the salt-like material composed of $C{a^{2 + }}$ and ${P^{3 - }}$. Calcium phosphide is also used in fireworks, torpedoes, self-igniting naval pyrotechnic flares, and various water-activated ammunition. Calcium phosphide is a common impurity in calcium carbide, which may cause the resulting phosphine-contaminated acetylene to ignite spontaneously. Sometimes there is confusion between valency and oxidation state. Valency is the number of electrons present in the outermost shell of an atom of a particular element whereas oxidation state is the number of electrons that an element in a particular compound has lost or gained.

Note:
We have to know that the oxidation state of an atom is not regarded as the real charge of the atom. In a chemical reaction if there is an increase in oxidation state then it is known as oxidation whereas if there is a decrease in oxidation state, it is known as reduction.