Problem 63 - 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 \(\mathrm{PBr}_{3},(\mathrm{c})\) reduction of \(\mathrm{PBr}_{3}\) to \(\mathrm{P}_{4}\) in the gas phase, \(\mathrm{using} \mathrm{H}_{2}\)

Step-by-Step Solution

Answer

The balanced chemical equations for the given reactions are: a) \(2 \mathrm{Ca_3(PO_4)_2} + 10 \mathrm{C} + 6 \mathrm{SiO_2} \longrightarrow \mathrm{P_4} + 6 \mathrm{CaSiO_3} + 10 \mathrm{CO}\) b) \(\mathrm{PBr_3} + 3 \mathrm{H_2O} \longrightarrow \mathrm{H_{3}PO_3} + 3 \mathrm{HBr}\) c) \(6 \mathrm{PBr_3} + 6 \mathrm{H_2} \longrightarrow 2 \mathrm{P_4} + 18 \mathrm{HBr}\)

Step 1: Identifying the reactants and products

In this reaction, the reactant is calcium phosphate (Ca₃(PO₄)₂) and we need to prepare white phosphorus (P₄) as the product. To separate phosphorus from calcium, we will use carbon and silicon dioxide. The final reactants and products are: Ca₃(PO₄)₂, C, SiO₂ ⟶ P₄, CaSiO₃, CO

Step 2: Balancing the chemical equation

Now, let's balance the chemical equation by adjusting the stoichiometric coefficients of the reactants and products: 2 Ca₃(PO₄)₂ + 10 C + 6 SiO₂ ⟶ P₄ + 6 CaSiO₃ + 10 CO The final balanced equation for the reaction is: \[2 \mathrm{Ca_3(PO_4)_2} + 10 \mathrm{C} + 6 \mathrm{SiO_2} \longrightarrow \mathrm{P_4} + 6 \mathrm{CaSiO_3} + 10 \mathrm{CO}\] #b) Hydrolysis of PBr3#

Step 1: Identifying the reactants and products

In this reaction, the reactant is PBr₃ and we need to hydrolyze it using water (H₂O). The final reactants and products are: PBr₃, H₂O ⟶ \(\mathrm{H}_{\mathrm{3}}\)PO₃, \(\mathrm{HBr}\)

Step 2: Balancing the chemical equation

Now, let's balance the chemical equation by adjusting the stoichiometric coefficients of the reactants and products: PBr₃ + 3 H₂O ⟶ \(\mathrm{H}_{\mathrm{3}}\)PO₃ + 3 \(\mathrm{HBr}\) The final balanced equation for the reaction is: \[\mathrm{PBr_3} + 3 \mathrm{H_2O} \longrightarrow \mathrm{H_{3}PO_3} + 3 \mathrm{HBr}\] #c) Reduction of PBr3 to P4 in the gas phase using H2#

Step 1: Identifying the reactants and products

In this reaction, the reactant is PBr₃, which is to be reduced to P₄ in the presence of hydrogen gas (H₂). The product will be white phosphorus (P₄) and HBr. The final reactants and products are: PBr₃, H₂ ⟶ P₄, HBr

Step 2: Balancing the chemical equation

Now, let's balance the chemical equation by adjusting the stoichiometric coefficients of the reactants and products: 6 PBr₃ + 6 H₂ ⟶ 2 P₄ + 18 HBr The final balanced equation for the reaction is: \[6 \mathrm{PBr_3} + 6 \mathrm{H_2} \longrightarrow 2 \mathrm{P_4} + 18 \mathrm{HBr}\]

Key Concepts

Stoichiometry

Stoichiometry is akin to a recipe for chemistry. It relates the quantities of reactants and products in a chemical reaction. This concept ensures that the law of conservation of mass is adhered to, meaning that the mass of the reactants must equal the mass of the products.

For example, in the preparation of white phosphorus from calcium phosphate, the balanced stoichiometric equation is essential. The amount of carbon and silicon dioxide must be carefully measured against calcium phosphate to produce the correct amounts of white phosphorus, calcium silicate, and carbon monoxide. Mastery of stoichiometry is crucial for predicting yields of products and for understanding the quantitative aspects of chemical reactions.

Chemical Reaction

A chemical reaction involves the transformation of one set of chemical substances to another. Chemists use chemical equations to depict such transformations. The starting substances, known as reactants, undergo a reaction to form new substances called products.

In the balanced equations presented, you can see how white phosphorus, phosphorous acid, and white phosphorus again, but under different conditions, are each produced through distinct chemical reactions, demonstrating the diverse ways elements combine and change. From hydrolysis to reduction, each chemical reaction has its unique requirements and outcomes, governed by the nature of reactants and conditions present.

Hydrolysis

Hydrolysis is a specific type of chemical reaction where a compound reacts with water, causing the decomposition of the compound and formation of new substances.

In the equation showcasing the hydrolysis of PBr₃, water reacts with PBr₃ to produce phosphorous acid (H₃PO₃) and hydrogen bromide (HBr). Hydrolysis often involves the breaking of bonds in the reactant molecule, here the PBr bonds, coupled with the addition of water's 'H' and 'OH' fragments to the resulting fragments of the reactant molecule, illustrating the transformational power of hydrolysis in chemistry.

Reduction Reaction

A reduction reaction can be simply described as the gain of electrons by a molecule, atom, or ion. It is often accompanied by a decrease in oxidation state. In a broader context, it includes any process in which an element gains hydrogen or loses oxygen.

The reduction of PBr₃ to P₄ using hydrogen gas (H₂) is an example where PBr₃ is reduced to elemental phosphorus (P₄), and H₂ is oxidized to HBr. Understanding reduction reactions is vital to grasp various chemical processes, such as those occurring in metabolism, batteries, and corrosion prevention.

Phosphorus Compounds

Phosphorus is a versatile element, forming various compounds with different properties and uses. In the provided reactions, we encounter diverse phosphorus compounds, like calcium phosphate, white phosphorus, and phosphorous acid.

Each compound contains phosphorus in different oxidation states and bonding environments. Through chemical reactions such as synthesis, hydrolysis, and reduction, we transform these compounds, altering their states, and in some cases, unlocking new uses. Understanding the chemistry of phosphorus compounds not only broadens our knowledge of inorganic chemistry but also informs our approach to handling and using these substances in real-world applications.