Problem 103 - A Complete Resource Book in Chemistry for JEE Main

Question

One mole of fluorine is reacted with two mole of hot and concentrated KOH. The products formed are \(\mathrm{KF}, \mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{O}_{2} .\) The molar ratio of \(\mathrm{KF}, \mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{O}_{2}\) respectively is (a) \(1: 2: 1\) (b) \(1: 2: 2\) (c) \(0.5: 1: 2\) (d) \(2: 1: 0.5\)

Step-by-Step Solution

Answer

The molar ratio is (d) 2:1:0.5.

Step 1: Write the Balanced Chemical Equation

In this reaction, fluorine gas reacts with potassium hydroxide to form potassium fluoride, water, and oxygen gas. The unbalanced equation is: \[ \text{F}_2 + \text{KOH} \rightarrow \text{KF} + \text{H}_2\text{O} + \text{O}_2 \]

Step 2: Balance the Atoms in the Reaction

To balance the reaction, first balance the number of fluorine atoms. There are 2 fluorine atoms in \(\text{F}_2\), so you need 2 potassium fluoride (\(\text{KF}\)). This gives: \[ \text{F}_2 + 2 \text{KOH} \rightarrow 2 \text{KF} + \text{H}_2\text{O} + \text{O}_2 \]. Next, balance the potassium atoms (the 2 KOH molecules provide 2 potassium atoms needed for the 2 \(\text{KF}\)). Balance the oxygen atoms: there are a total of 4 oxygen atoms on the right side (2 from water and 2 from oxygen gas) and 2 from 2 KOH, which is already consistent. Finally, balance the hydrogen: there are 2 hydrogen atoms on both sides.Thus, the balanced equation is: \[ \text{F}_2 + 2 \text{KOH} \rightarrow 2 \text{KF} + \text{H}_2\text{O} + 0.5\text{O}_2 \].

Step 3: Determine the Molar Ratios

From the balanced equation, we can see that one mole of fluorine reacts with two moles of KOH to produce two moles of KF, one mole of water and 0.5 moles of oxygen gas. Therefore, the molar ratio of \(\text{KF}\) to \(\text{H}_2\text{O}\) to \(\text{O}_2\) is 2:1:0.5.

Key Concepts

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships among reactants and products in a chemical reaction. It allows us to predict the amounts of substances consumed and produced in a given reaction. To use stoichiometry effectively, it's crucial to start with a balanced chemical equation. This is because the coefficients in a balanced equation represent the exact ratio of moles of each substance involved in the reaction. The key points of stoichiometry include:

• Understanding the mole ratio from the coefficients in the balanced equation.
• Using this ratio to calculate the amounts of reactants needed or products formed.

For instance, in our balanced equation: \[ \text{F}_2 + 2 \text{KOH} \rightarrow 2 \text{KF} + \text{H}_2\text{O} + 0.5\text{O}_2 \]This shows that 1 mole of \( \text{F}_2 \) reacts with 2 moles of \( \text{KOH} \) to produce 2 moles of \( \text{KF} \), 1 mole of water, and 0.5 moles of oxygen. Thus, stoichiometry gives us the essential quantitative relationship needed to predict the outcomes of chemical reactions.

Mole Concept

The mole concept is a fundamental principle in chemistry that relates the amount of a substance to its mass and number of entities, such as atoms or molecules. One mole of any substance contains Avogadro's number of entities, which is approximately \( 6.022 \times 10^{23} \). This concept is vital in converting between different units of measurement in chemistry, such as from mass to moles.In the context of chemical reactions, knowing the number of moles of each reactant and product can help determine how much of each substance is needed or produced. In our example, we understand that:

• 1 mole of fluorine molecules \( \text{F}_2 \) is involved.
• 2 moles of potassium hydroxide \( \text{KOH} \) react to form products.
• The reaction produces 2 moles of potassium fluoride \( \text{KF} \), 1 mole of water \( \text{H}_2\text{O} \), and 0.5 moles of oxygen \( \text{O}_2 \).

Understanding the mole concept helps us make these calculations and apply them practically in laboratory settings, as it directly ties the theoretical aspects of chemical reactions to measurable quantities.

Reaction Equations

A reaction equation is a symbolic representation of a chemical reaction. It expresses what reactants are transformed into products and in what proportions. The equation must be balanced, meaning the number of atoms for each element is the same on both sides of the equation. This ensures that the law of conservation of mass is upheld, which states that matter cannot be created or destroyed in a chemical reaction.In the equation we've discussed:\[ \text{F}_2 + 2 \text{KOH} \rightarrow 2 \text{KF} + \text{H}_2\text{O} + 0.5\text{O}_2 \]Each component plays a role:

• Reactants: \( \text{F}_2 \) and \( \text{KOH} \).
• Products: \( \text{KF} \), \( \text{H}_2\text{O} \), and \( \text{O}_2 \).
• The coefficients reflect the exact number of moles that participate in the reaction.

Every reaction equation serves as a blueprint that guides how chemical processes should be performed. By practicing equation balancing and recognizing products and reactants, students can accurately predict reaction outcomes and apply this knowledge in experiments and computations.