Problem 33 - A Complete Resource Book in Chemistry for JEE Main

Question

One mole of calcium phosphide on reaction with excess water gives (a) one mole of phosphine (b) two moles of phosphoric acid (c) two moles of phosphine (d) one mole of phosphorus pentroxide

Step-by-Step Solution

Answer

Two moles of phosphine are produced.

Step 1: Identify Given Chemical Reaction

The problem involves the reaction of calcium phosphide with water. Calcium phosphide is chemically represented as \( \text{Ca}_3\text{P}_2 \).

Step 2: Write Balanced Chemical Equation

Calcium phosphide \( (\text{Ca}_3\text{P}_2) \) reacts with water \( (\text{H}_2\text{O}) \) to produce calcium hydroxide \( (\text{Ca(OH)}_2) \) and phosphine \( (\text{PH}_3) \). The balanced chemical equation is: \[ \text{Ca}_3\text{P}_2 + 6\text{H}_2\text{O} \rightarrow 3\text{Ca(OH)}_2 + 2\text{PH}_3 \]

Step 3: Analyze the Stoichiometry

The balanced equation shows that one mole of \( \text{Ca}_3\text{P}_2 \) reacts to produce two moles of phosphine \( \text{PH}_3 \).

Step 4: Select Correct Option

Based on the reaction stoichiometry, option (c), "two moles of phosphine," is correct.

Key Concepts

Stoichiometry

Stoichiometry is a key concept in chemistry that helps you understand the quantitative relationships within a chemical reaction. When you have a balanced chemical equation, stoichiometry allows you to predict the amounts of products and reactants involved. This is done by using the coefficients from the balanced equation to create ratios.Here's a simple way to visualize it:

• Each coefficient in a chemical equation tells you the number of moles of a substance.
• This ratio helps compute how much of each substance is needed or produced.

In the reaction of calcium phosphide (\( \text{Ca}_3\text{P}_2 \)) with water (\( \text{H}_2\text{O} \)), stoichiometry is used to determine that one mole of calcium phosphide produces two moles of phosphine (\( \text{PH}_3 \)).
This means for every mole of \( \text{Ca}_3\text{P}_2 \), two moles of phosphine are produced. Stoichiometry is crucial for accurately predicting yields in chemical reactions.

Balanced Chemical Equation

A balanced chemical equation is fundamental in chemistry because it obeys the law of conservation of mass. This law states that mass cannot be created or destroyed in a chemical reaction; hence, the same amount of atoms must be present before and after a reaction.To write a balanced chemical equation:

• Identify each compound and the total number of atoms of each element on both sides of the equation.
• Adjust coefficients so that these totals are equal on both sides.

In the calcium phosphide reaction:\[\text{Ca}_3\text{P}_2 + 6\text{H}_2\text{O} \rightarrow 3\text{Ca(OH)}_2 + 2\text{PH}_3\]you can see that the coefficients balance the number of calcium, phosphorus, oxygen, and hydrogen atoms on both sides. This balancing ensures that the chemical reaction obeys the mass conservation principle, allowing accurate stoichiometric calculations.

Calcium Phosphide Reaction

Calcium phosphide (\( \text{Ca}_3\text{P}_2 \)) reacts with water (\( \text{H}_2\text{O} \)) in an interesting chemical reaction, producing calcium hydroxide (\( \text{Ca(OH)}_2 \)) and phosphine (\( \text{PH}_3 \)). This reaction can be represented by the balanced equation:\[\text{Ca}_3\text{P}_2 + 6\text{H}_2\text{O} \rightarrow 3\text{Ca(OH)}_2 + 2\text{PH}_3\]This reaction has practical applications and is notable in chemistry for the production of phosphine gas, which is a colorless and flammable gas often used as an agricultural fumigant.Here are key points about this reaction:

• Calcium phosphide reacts vigorously with water.
• It releases phosphine gas, which is hazardous and has a smell of garlic or decaying fish.
• Calcium hydroxide, also known as slaked lime, is produced in the reaction.

By understanding this reaction, you get insights into how chemical transformations occur, which is crucial in industrial applications and laboratory experiments.