Problem 37 - A Complete Resource Book in Chemistry for JEE Main

Question

\(\mathrm{P}_{2} \mathrm{O}_{5}\) is heated with water to give (a) hypophosphoric acid (b) orthophosphoric acid (c) hypophosphorus acid (d) phosphorus acid

Step-by-Step Solution

Answer

(b) orthophosphoric acid

Step 1: Understand the Reactants

We need to identify the compounds involved in the reaction. We're heating diphosphorus pentoxide, \( \mathrm{P}_{2}\mathrm{O}_{5} \), with water, \( \mathrm{H}_{2}\mathrm{O} \). We will determine what types of acids can be formed from this reaction.

Step 2: Identify the Possible Products

When \( \mathrm{P}_{2}\mathrm{O}_{5} \) reacts with water, it can produce different types of phosphoric acids. The question gives us four possible acids: hypophosphoric acid, orthophosphoric acid, hypophosphorus acid, and phosphorus acid. We need to determine which one of these forms from the reaction.

Step 3: Recall Chemical Reaction Patterns

From chemistry knowledge, we know that \( \mathrm{P}_{2}\mathrm{O}_{5} \) reacts with an excess amount of water to produce orthophosphoric acid. The balanced chemical equation is:\[\mathrm{P}_{2}\mathrm{O}_{5} + 3\mathrm{H}_{2}\mathrm{O} \rightarrow 2\mathrm{H}_{3}\mathrm{PO}_{4}\]This indicates that orthophosphoric acid, \( \mathrm{H}_{3}\mathrm{PO}_{4} \), is formed.

Step 4: Confirm the Correct Answer

Based on the balanced equation from Step 3, the reaction of \( \mathrm{P}_{2}\mathrm{O}_{5} \) with water yields orthophosphoric acid. Therefore, the correct choice is (b) orthophosphoric acid.

Key Concepts

Understanding the Diphosphorus Pentoxide Reaction

Diphosphorus pentoxide, denoted as \( \mathrm{P}_2\mathrm{O}_5 \), is a chemical compound that plays a significant role in the formation of phosphoric acids when reacted with water. When \( \mathrm{P}_2\mathrm{O}_5 \) is heated and comes into contact with water, a chemical reaction occurs which typically leads to the formation of phosphoric acids, primarily orthophosphoric acid. This type of reaction is essential to understand in the context of synthesis and production of various acid compounds utilized in different industrial and chemical processes.

In its dry state, diphosphorus pentoxide is a white crystalline solid. It is highly hygroscopic, meaning it readily absorbs moisture from the air. This characteristic makes it an effective dehydrating agent. When it interacts with water, a vigorous reaction ensues, producing a solution or syrupy liquid depending on the quantity of water involved.

The balanced chemical equation illustrating the transformation of \( \mathrm{P}_2\mathrm{O}_5 \) to orthophosphoric acid is crucial for predicting the products of this reaction. This predictive ability is integral in controlling and understanding chemical manufacturing processes.

Deciphering Chemical Equations

Chemical equations serve as powerful tools for depicting chemical reactions. In the context of the \( \mathrm{P}_2\mathrm{O}_5 \) reaction with water, the chemical equation succinctly summarizes what happens during the reaction. The balanced equation is as follows:

\[\mathrm{P}_2\mathrm{O}_5 + 3\mathrm{H}_2\mathrm{O} \rightarrow 2\mathrm{H}_3\mathrm{PO}_4\]

This equation tells us a few vital things:

• The reactants: diphosphorus pentoxide \( \mathrm{P}_2\mathrm{O}_5 \) and water \( \mathrm{H}_2\mathrm{O} \).
• The products: orthophosphoric acid \( \mathrm{H}_3\mathrm{PO}_4 \).
• The stoichiometry, indicating that three moles of water are required for each mole of \( \mathrm{P}_2\mathrm{O}_5 \) to form two moles of \( \mathrm{H}_3\mathrm{PO}_4 \).

Understanding and interpreting chemical equations is critical because it informs chemists about the quantitative aspects of reactants and products involved in chemical reactions. Chemical equations provide insights into the conservation of mass, where the total mass of reactants equals the total mass of products, ensuring that every atom is accounted for throughout the reaction.

Insight into Phosphoric Acids

Phosphoric acids are a group of important compounds in chemistry. They are characterized by a central phosphorus atom surrounded by oxygen and sometimes hydrogen. In this exercise, the focus is on orthophosphoric acid, also represented as \( \mathrm{H}_3\mathrm{PO}_4 \). It is the most common and widely used phosphoric acid, known for its use in fertilizers, food flavorings, and cleaning agents.

Here are some useful facts about orthophosphoric acid:

• It is a non-toxic acid, making it suitable for use in food and beverages.
• It acts as a weak acid, which means it does not completely dissociate in water.
• It is a tribasic acid, possessing three replaceable hydrogen atoms.
• Its versatile nature makes it valuable in many industrial and laboratory applications.

Understanding phosphoric acids, particularly orthophosphoric acid, is not only fundamental to chemistry but also to a variety of industries. Their chemical properties and uses highlight the importance of controlled reactions, such as that of \( \mathrm{P}_2\mathrm{O}_5 \) with water. This knowledge assists scientists and industries in generating compounds with specific characteristics for different applications.