Question

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

Short answer

Pair (a) and (d) do not form oxygen.

Step-by-step solution

Identify the type of reactions

Understand that each pair of reactants can undergo specific types of chemical reactions. The possible generation of oxygen depends on the chemical properties of the reactants and their combinations.

Examine pair (a): \( \mathrm{Cl}_y, \mathrm{NaOH} \) solution (cold, dilute)

In the presence of cold, dilute \( \mathrm{NaOH} \), chlorine reacts to form hypochlorite: \( \mathrm{Cl}_2 + 2 \mathrm{NaOH} \rightarrow \mathrm{NaCl} + \mathrm{NaOCl} + \mathrm{H}_2\mathrm{O} \). This does not result in the formation of \( \mathrm{O}_2 \).

Examine pair (b): \( \mathrm{F}_2, \mathrm{NaOH} \) solution (hot, conc.)

Fluorine is very reactive and reacts with hot, concentrated \( \mathrm{NaOH} \) to form sodium fluoride, oxygen, and water: \( 2 \mathrm{F}_2 + 4 \mathrm{NaOH} \rightarrow 4 \mathrm{NaF} + \mathrm{O}_2 + 2 \mathrm{H}_2\mathrm{O} \). This reaction produces \( \mathrm{O}_2 \).

Examine pair (c): \( \mathrm{F}_2, \mathrm{H}_2\mathrm{O} \)

\( \mathrm{F}_2 \) reacts with water very vigorously to produce hydrogen fluoride and release oxygen gas: \( 2 \mathrm{F}_2 + 2 \mathrm{H}_2\mathrm{O} \rightarrow 4 \mathrm{HF} + \mathrm{O}_2 \). Oxygen is formed in this reaction.

Examine pair (d): \( \mathrm{Ca(OCl)_2}, \mathrm{H}_2\mathrm{SO}_4 \) (dilute, small amount)

Reacting calcium hypochlorite with dilute sulfuric acid releases chlorine gas and not oxygen: \( \mathrm{Ca(OCl)_2} + \mathrm{H}_2\mathrm{SO}_4 \rightarrow \mathrm{CaSO}_4 + 2\mathrm{HClO} \). This does not form \( \mathrm{O}_2 \).

Key concepts

Chemical Reactions

Chemical reactions are at the heart of understanding how substances transform. When two or more substances interact to form new products, we call this a chemical reaction. Reactants are the starting materials, and products are the new materials formed.
Understanding each reaction requires knowing the characteristics of the reactants and the conditions under which they interact. For example:

• Adding heat can speed up a reaction by providing energy to break bonds.
• Using a catalyst can lower the activation energy needed.
• The concentration and state (such as liquid or gas) of reactants also matter.

Each chemical reaction can usually be classified into categories like synthesis, decomposition, single replacement, and double replacement. In our exercise, the absence of oxygen formation in reaction patterns a and d stems from the specific chemical interactions. For pair (a), the cold, dilute condition of the NaOH solution leads chlorine to form hypochlorite instead of oxygen. Similarly, in pair (d), calcium hypochlorite reacts with sulfuric acid to release chlorine, not oxygen.

Reaction Mechanisms

Reaction mechanisms break down the complex steps of a chemical reaction into simpler, understandable stages. Each reaction step involves specific changes at the molecular level and often includes intermediate substances that usually don't appear in the overall chemical equation.
Let's apply this to the exercise at hand:

• For pair (b), fluorine reacts with hot, concentrated NaOH in multiple steps, eventually producing oxygen. The breakdown into sodium fluoride and the resultant release of oxygen are part of these steps.
• In the case of pair (c), the vigorous reaction of fluorine with water quickly produces hydrogen fluoride and oxygen gas, showing the speed and robust energy transfer involved.

Understanding the mechanism allows us to predict and explain the types and quantities of products formed. It also clarifies why some conditions might favor certain reactions, while others do not. Studying reaction kinetics, or the rate at which these mechanisms proceed, helps in optimizing and controlling chemical processes for better yield and efficiency.

Inorganic Chemistry

Inorganic chemistry, a critical branch of chemistry, deals with compounds not based on carbon-hydrogen bonds, primarily focusing on minerals, metals, and the various inorganic compounds. Understanding inorganic compounds and their reactions is essential, especially as they relate to elements like halogens and oxides, which are central to many industrial processes.
This branch of chemistry involves studying elemental reactions, like those in our exercise:

• Halogens, such as chlorine and fluorine in our exercise, display varying reactivities. Fluorine is highly reactive, even with water, highlighting the vigorous reactions and conditions that have to be managed.
• Compounds like sodium hydroxide (NaOH) and calcium hypochlorite (Ca(OCl)_2) are frequently used in industries for neutralizations or as bleaching agents, reflecting their importance in inorganic chemistry.

By understanding reactions like the ones in the exercise, students learn the importance of inorganic reactions in broader applications, including water treatment, material synthesis, and beyond.