Problem 51 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following pairs of reactant does not form oxygen when they react with each other? (a) \(\mathrm{Cl}_{2}, \mathrm{NaOH}\) solution (cold, dilute) (b) \(\mathrm{F}_{2}, \mathrm{NaOH}\) solution (hot, concentrated) (c) \(\mathrm{F}_{2}^{2}, \mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{CaOCl}_{2}, \mathrm{H}_{2} \mathrm{SO}_{4}\) (dilute)

Step-by-Step Solution

Answer

Option A does not produce oxygen.

Step 1: Understand the Reactions

For each option, we need to consider the chemical reaction and whether it produces oxygen. We'll examine each reaction separately.

Step 2: Option A Reaction

Option A combines chlorine gas \( \mathrm{Cl}_2 \) with a cold, dilute sodium hydroxide \( \mathrm{NaOH} \) solution. No oxygen is produced as the reaction forms \( \mathrm{NaClO} \), \( \mathrm{NaCl} \), and water: \[ \mathrm{Cl}_2 + 2 \mathrm{NaOH} \rightarrow \mathrm{NaClO} + \mathrm{NaCl} + \mathrm{H}_2\mathrm{O} \].

Step 3: Option B Reaction

Option B uses \( \mathrm{F}_2 \) with a hot, concentrated \( \mathrm{NaOH} \) solution. The reaction releases oxygen: \[ 2\mathrm{F}_2 + 2\mathrm{NaOH} \rightarrow \mathrm{OF}_2 + 2\mathrm{NaF} + \mathrm{H}_2\mathrm{O} \]. Oxygen is present here.

Step 4: Option C Reaction

In Option C, \( \mathrm{F_2} \) reacts with water. This produces oxygen: \[ 2\mathrm{F}_2 + 2\mathrm{H}_2\mathrm{O} \rightarrow 4\mathrm{HF} + \mathrm{O}_2 \]. Oxygen is indeed formed.

Step 5: Option D Reaction

Option D involves calcium hypochlorite \( \mathrm{Ca(OCl)_2} \) with dilute sulfuric acid \( \mathrm{H}_2\mathrm{SO}_4 \). This reaction produces chlorine, water, and calcium sulfate but not oxygen:\[ \mathrm{Ca(OCl)_2} + \mathrm{H}_2\mathrm{SO}_4 \rightarrow 2\mathrm{HClO} + \mathrm{CaSO_4} \].

Key Concepts

Chlorine and Sodium Hydroxide Reaction

When chlorine gas (\( \mathrm{Cl}_2 \)) reacts with a cold, dilute solution of sodium hydroxide (\( \mathrm{NaOH} \)), a fascinating reaction occurs that does not produce oxygen. Instead, it leads to the formation of sodium chloride (\( \mathrm{NaCl} \)), sodium hypochlorite (\( \mathrm{NaClO} \)), and water. This kind of reaction is very common in producing bleach solutions. Sodium hypochlorite is the active ingredient in bleach. It is widely used for cleaning and disinfection purposes. The balanced chemical equation for this reaction is: \[ \mathrm{Cl}_2 + 2 \mathrm{NaOH} \rightarrow \mathrm{NaClO} + \mathrm{NaCl} + \mathrm{H}_2\mathrm{O} \]. Some important points about this reaction include:

• It's an example of a disproportionation reaction because chlorine is both reduced and oxidized.
• No oxygen gas is produced during this process.
• Sodium hypochlorite is beneficial for cleaning and sanitation.

Fluorine and Water Reaction

The reaction between fluorine \( \mathrm{F}_2 \) and water \( \mathrm{H}_2\mathrm{O} \) is vigorous and interesting because it produces oxygen gas. Fluorine is incredibly reactive, and its interaction with water leads to the formation of hydrogen fluoride (\( \mathrm{HF} \)) and oxygen gas (\( \mathrm{O}_2 \)). The balanced equation for this reaction is: \[ 2\mathrm{F}_2 + 2\mathrm{H}_2\mathrm{O} \rightarrow 4\mathrm{HF} + \mathrm{O}_2 \].Key takeaways about this reaction:

• The reaction shows the high reactivity of fluorine, especially its ability to oxidize water.
• Oxygen is clearly formed as a by-product.
• Due to the reactivity, handling of fluorine requires extreme caution.

Calcium Hypochlorite and Sulfuric Acid

Calcium hypochlorite \( \mathrm{Ca(OCl)_2} \) when combined with dilute sulfuric acid \( \mathrm{H}_2\mathrm{SO}_4 \) is another reaction scenario where no oxygen is produced. Instead, this combination yields hypochlorous acid (\( \mathrm{HClO} \)), calcium sulfate (\( \mathrm{CaSO_4} \)), and water. The balanced chemical equation for this reaction is: \[ \mathrm{Ca(OCl)_2} + \mathrm{H}_2\mathrm{SO}_4 \rightarrow 2\mathrm{HClO} + \mathrm{CaSO_4} \].Considerations about this reaction include:

• This mixture is often used in disinfection processes.
• No elemental oxygen is released in the reaction.
• Calcium sulfate is an inert solid, sometimes seen as a precipitate in the solution.

Chemical Reaction Analysis

Chemical reaction analysis allows us to determine whether oxygen gas is produced during a chemical process. By examining the different reactants and products involved, we can accurately predict the outcome. Analyzing potential reactions involves:

• Writing balanced chemical equations to understand the complete reaction process.
• Identifying changes in the oxidation states of elements to determine if oxidation or reduction occurs.
• Distinguishing whether reactions involve the formation of gases, such as oxygen, by extracting information on all products formed.

Efficient chemical reaction analysis can help predict products, safety concerns, and potential applications of chemical reactions.