Problem 35 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

One mole of calcium phosphide on reaction with excess water gives [1999-2 Marks] (a) one mole of phosphine (b) two moles of phosphoric acid (c) two moles of phosphine (d) one mole of phosphorus pentoxide

Step-by-Step Solution

Answer

One mole of calcium phosphide produces two moles of phosphine, answer (c).

Step 1: Write the Balanced Chemical Equation

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

Step 2: Analyze the Stoichiometry

From the balanced equation, 1 mole of calcium phosphide \((\text{Ca}_3\text{P}_2)\) produces 2 moles of phosphine \((\text{PH}_3)\). This is because the stoichiometric coefficient of \(\text{PH}_3\) is 2.

Step 3: Determine the Correct Answer

Since 1 mole of calcium phosphide produces 2 moles of phosphine, the correct choice in response to the original question is (c) two moles of phosphine.

Key Concepts

Balanced Chemical Equation

Understanding a balanced chemical equation is the key to mastering chemical reactions. In a balanced equation, the number of atoms of each element is equal on both sides of the equation. This reflects the Law of Conservation of Mass, which tells us that mass is neither created nor destroyed in a chemical reaction. Let's look at the reaction between calcium phosphide and water:

• The equation is: \( \text{Ca}_3\text{P}_2 + 6\text{H}_2\text{O} \rightarrow 3\text{Ca(OH)}_2 + 2\text{PH}_3 \).
• Here, you see that there are equal numbers of each type of atom (calcium, phosphorus, hydrogen, and oxygen) on both sides.
• Balancing such equations ensures that you correctly understand the reacting masses or moles of the substances involved.

Balancing equations requires adjusting the coefficients before each compound until each element has the same number of atoms on both sides. By mastering this skill, you can solve many chemistry problems with confidence.

Stoichiometry

Stoichiometry is a crucial concept in chemistry that involves the calculation of reactants and products in chemical reactions. It gives us insight into how much of each substance is involved and produced. In our example with calcium phosphide:

• The balanced equation shows that 1 mole of \( \text{Ca}_3\text{P}_2 \) reacts to produce 2 moles of \( \text{PH}_3 \).
• Stoichiometry involves using the coefficients from the balanced equation to determine the relationship between the quantities of reactants and products.
• It allows chemists to predict the amounts of substances consumed and produced using a proportional method.

To solve stoichiometric problems, you need to be familiar with mole-to-mole conversions based on the balanced chemical equation. This forms the foundation for more complex calculations involving volumes and masses in chemical reactions.

Phosphine Production

Phosphine, a gaseous compound with the formula \( \text{PH}_3 \), is a product of the reaction between calcium phosphide and water. It plays a significant role in various chemical industries. Here's a closer look:

• Phosphine is produced in a reaction that involves calcium phosphide \( \text{Ca}_3\text{P}_2 \) and water \( \text{H}_2\text{O} \).
• The balanced chemical equation from earlier indicates that 1 mole of \( \text{Ca}_3\text{P}_2 \) yields 2 moles of phosphine \( \text{PH}_3 \).
• This reaction is noteworthy because phosphine itself is often used as a fumigant in agriculture to protect stored grains.

Understanding how phosphine is produced and its applications can provide insights into its importance in industrial and agricultural contexts. Moreover, this aligns with learning about chemical reactions and product yields.