Problem 67 - Chemistry: The Central Science

Question

Write a balanced equation for each of the following reactions: (a) preparation of white phosphorus from calcium phosphate, (b) hydrolysis of \(\mathrm{PBr}_{3}\), (c) reduction of \(\mathrm{PBr}_{3}\) to \(\mathrm{P}_{4}\) in the gas phase, using \(\mathrm{H}_{2}\).

Step-by-Step Solution

Answer

The balanced equations for the given reactions are as follows: (a) \(2 \ Ca_{3}(PO_{4})_{2} + 10 \ C \rightarrow 6 \ CaO + 10 \ CO + P_{4}\) (b) \(PBr_{3} + 3 \ H_{2}O \rightarrow H_{3}PO_{3} + 3 \ HBr\) (c) \(2 \ PBr_{3} + 3 \ H_{2} \rightarrow P_{4} + 6 \ HBr\)

Step 1: Reaction 1: Preparation of white phosphorus from calcium phosphate

First, we need to identify the reactants and products. Calcium phosphate is the reactant, and white phosphorus is the product. The reaction also requires a reducing agent which is often carbon (C) in the form of coke or coal. The products of the reaction are calcium phosphate and carbon monoxide (CO). The balanced equation is: \(2 \ Ca_{3}(PO_{4})_{2} + 10 \ C \rightarrow 6 \ CaO + 10 \ CO + P_{4}\)

Step 2: Reaction 2: Hydrolysis of PBr3

In this reaction, PBr3 reacts with water (H2O). The products are phosphorous acid (H3PO3) and hydrobromic acid (HBr). The balanced equation is: \(PBr_{3} + 3 \ H_{2}O \rightarrow H_{3}PO_{3} + 3 \ HBr\)

Step 3: Reaction 3: Reduction of PBr3 to P4 using H2

In this gas-phase reduction reaction, PBr3 reacts with hydrogen gas (H2) to produce elemental phosphorus (P4) and hydrogen bromide (HBr). The balanced equation is: \(2 \ PBr_{3} + 3 \ H_{2} \rightarrow P_{4} + 6 \ HBr\)