Q22.41P - Chemistry: Molecular Nature Of Matter And Change

Question

Phosphorus is one of the impurities present in pig iron that is removed in the basic-oxygen process. Assuming phosphorus is present as P atoms, write equations for its oxidation and subsequent reaction in the basic slag.

Step-by-Step Solution

Answer

The reaction of phosphorus for the oxidation and reaction in basic slag is,

$$\begin{gathered} {\text{4P(l) + 5O}}_{\text{2}}\text{(g)}\to {\text{2P}}_{\text{2}}{\text{O}}_{\text{5}}\text{(l)} \\ {\text{P}}_{\text{2}}{\text{O}}_{\text{5}}\text{(l) + CaO(s)}\to {\text{Ca}}_{\text{3}}{\left({\text{PO}}_{\text{4}}\right)}_{\text{2}}\text{(l)} \end{gathered}$$

Step 1: Concept Introduction

During a reaction, when a molecule, atom, or ion loseselectrons, then that process or reaction is termed as an oxidation reaction.An enhanced state of any molecule, atom, or ion is enhanced, is called oxidation. On the other hand, when a molecule, atom, or ion during a reaction gains electrons, then that is termed as a reduction reaction which is opposite to oxidation reaction.

Step 2: Obtaining the Equation for Oxidation and Reaction of Phosphorus in Basic Slag

When pig iron with varied impurities is converted into steel in a furnace, the basic-oxygen process is used. The high-pressure ${\text{O}}_{\text{2}}$ passes through the molten iron, oxidising the impurities, according to the principle.

Basic oxidation occurs as follows, assuming the P atoms are present:

${\text{4P(l)+5O}}_{\text{2}}{\text{(g)→2P}}_{\text{2}}{\text{O}}_{\text{5}}\text{(l)}$

The oxides are transformed to a molten slag when a basic slag - calcium oxide - is added, and the iron is removed by decantation:

$\begin{array}{rcl}{\text{4P(l) + 5O}}_{\text{2}}\text{(g)}& \to & {\text{2P}}_{\text{2}}{\text{O}}_{\text{5}}\text{(l)}\\ {\text{P}}_{\text{2}}{\text{O}}_{\text{5}}\text{(l) + CaO(s)}& \to & {\text{Ca}}_{\text{3}}{\left({\text{PO}}_{\text{4}}\right)}_{\text{2}}\text{(l)}\end{array}$

Therefore, the oxidation equation is,

${\text{4P(l) + 5O}}_{\text{2}}\text{(g)}\to {\text{2P}}_{\text{2}}{\text{O}}_{\text{5}}\text{(l)}$

And the reaction in basic slag is,

${\text{P}}_{\text{2}}{\text{O}}_{\text{5}}\text{(l) + CaO(s)}\to {\text{Ca}}_{\text{3}}{\left({\text{PO}}_{\text{4}}\right)}_{\text{2}}\text{(l)}$.