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 \(P_{4}\) in the gas phase, using \(\mathrm{H}_{2}\).

Short answer

The three balanced equations are: 1. Preparation of white phosphorus from calcium phosphate: \[Ca_3(PO_4)_2 + 6SiO_2 + 10C \rightarrow 3CaSiO_3 + 10CO + 2P_4\] 2. Hydrolysis of \(\mathrm{PBr_3}\): \[PBr_3 + 3H_2O \rightarrow H_3PO_3 + 3HBr\] 3. Reduction of \(\mathrm{PBr_3}\) to \(P_4\) in the gas phase using \(\mathrm{H_2}\): \[6PBr_3 + 6H_2 \rightarrow P_4 + 18HBr\]

Step-by-step solution

Preparation of white phosphorus from calcium phosphate

To prepare white phosphorus from calcium phosphate, we typically use the following chemical reaction: \[Ca_3(PO_4)_2 + 6SiO_2 + 10C \rightarrow 3CaSiO_3 + 10CO + 2P_4\] In this reaction: - Calcium phosphate: \(Ca_3(PO_4)_2\) - Silica: \(6SiO_2\) - Carbon: \(10C\) - Calcium silicate: \(3CaSiO_3\) - Carbon monoxide: \(10CO\) - White phosphorus: \(2P_4\)

Hydrolysis of \(\mathrm{PBr}_{3}\)

For the hydrolysis of \(\mathrm{PBr}_3\), we have the following chemical reaction: \[PBr_3 + 3H_2O \rightarrow H_3PO_3 + 3HBr\] In this reaction: - Phosphorus tribromide: \(PBr_3\) - Water: \(3H_2O\) - Phosphorous acid: \(H_3PO_3\) - Hydrogen bromide: \(3HBr\)

Reduction of \(\mathrm{PBr}_{3}\) to \(P_{4}\) in the gas phase using \(\mathrm{H}_{2}\)

For the reduction of \(\mathrm{PBr}_3\) to \(P_4\) in the gas phase using \(\mathrm{H}_2\), we have the following chemical reaction: \[6PBr_3 + 6H_2 \rightarrow P_4 + 18HBr\] In this reaction: - Phosphorus tribromide: \(6PBr_3\) - Hydrogen gas: \(6H_2\) - White phosphorus: \(P_4\) - Hydrogen bromide: \(18HBr\)

Key concepts

Chemical Reaction

Understanding chemical reactions is fundamental in the study of chemistry. A chemical reaction involves the transformation of one or more substances, called reactants, into one or more new substances, known as products. This transformation occurs due to the breaking and forming of chemical bonds. A balanced chemical equation represents this process symbolically, showing the conservation of mass where the number of atoms of each element is the same on both sides of the equation.

For instance, in the preparation of white phosphorus, the reactants are calcium phosphate, silica, and carbon, and the products include calcium silicate, carbon monoxide, and white phosphorus. The balanced equation must accurately reflect the stoichiometry of the reactants and products involved: for every molecule of calcium phosphate used, a certain number of silica and carbon molecules react, resulting in precise quantities of each product.

White Phosphorus Preparation

White phosphorus is prepared industrially through a high-temperature reaction involving calcium phosphate, silica (sand), and carbon in the form of coke. This intricate process is vital in the manufacture of phosphorus-containing products.

In the balanced chemical equation provided, \(Ca_3(PO_4)_2 + 6SiO_2 + 10C \rightarrow 3CaSiO_3 + 10CO + 2P_4\), every reactant and product is accounted for, signifying the completeness of the reaction. Safety is also a critical consideration in white phosphorus preparation, as the substance is highly reactive and must be handled with extreme care.

Hydrolysis Reaction

Hydrolysis reactions are a type of chemical reaction wherein water is used to break down a compound. During hydrolysis, water molecules (\(H_2O\)) split into hydrogen and hydroxide ions, which then interact with the compound, leading to the breakdown of its molecular structure. Such reactions are common in biochemistry and various industrial processes.

The hydrolysis of phosphorus tribromide (\(PBr_3\)) provides a clear example: \(PBr_3 + 3H_2O \rightarrow H_3PO_3 + 3HBr\). In this reaction, water breaks down \(PBr_3\) into phosphorous acid (\(H_3PO_3\)) and hydrogen bromide (\(HBr\)), illustrating the typical outcome of hydrolysis where the reactant splits into smaller molecules.

Reduction Reaction

Reduction reactions are chemical processes where a molecule gains electrons, often through the addition of hydrogen or the removal of oxygen. This is a vital concept in chemistry, especially in the field of redox reactions which also includes its counterpart, oxidation. Reduction can be used to purify elements or create new chemical compounds.

In the reduction of \(PBr_3\) using hydrogen gas (\(H_2\)), the balanced equation \(6PBr_3 + 6H_2 \rightarrow P_4 + 18HBr\) shows \(PBr_3\) gaining hydrogen electrons, resulting in the formation of white phosphorus (\(P_4\)) and hydrogen bromide (\(HBr\)). This reaction is an excellent example of how reduction processes can transform a substance to a more elemental form.