Problem 31 - A Complete Resource Book in Chemistry for JEE Main

Question

The pair of compounds which cannot exist together is (a) \(\mathrm{NaHCO}_{3}\) and \(\mathrm{NaOH}\) (b) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(\mathrm{NaHCO}_{3}\) (c) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) and \(\mathrm{NaOH}\) (d) \(\mathrm{NaHCO}_{3}\) and \(\mathrm{NaCl}\)

Step-by-Step Solution

Answer

The pair that cannot coexist is (a) NaHCO3 and NaOH.

Step 1: Analyze Compound Pairs

We need to assess the chemical properties of each pair. Specifically, we are looking for reactions that would prevent the compounds from coexisting.

Step 2: Check NaHCO3 and NaOH

Sodium bicarbonate (NaHCO3) is acidic in nature, and sodium hydroxide (NaOH) is a strong base. The two will react with each other to form sodium carbonate (Na2CO3), water, and carbon dioxide. The reaction formula is: NaHCO3 + NaOH  Na2CO3 + H2O + CO2.

Step 3: Check Na2CO3 and NaHCO3

These two compounds can coexist because both are forms of sodium carbonate, and no significant reaction occurs between them under normal conditions.

Step 4: Check Na2CO3 and NaOH

Both compounds are basic in nature and do not react with each other. They can coexist as they do not undergo any reaction together.

Step 5: Check NaHCO3 and NaCl

Sodium bicarbonate (NaHCO3) and sodium chloride (NaCl) can coexist without any reaction since they are quite stable together.

Step 6: Identify the Non-coexisting Pair

From the analysis, the pair that cannot exist together is NaHCO3 and NaOH, because they react to form Na2CO3, H2O, and CO2.

Key Concepts

Acid-Base Reaction

An acid-base reaction is a chemical process where an acid reacts with a base to form water and a salt. In these reactions, acids donate hydrogen ions (H\(^+\)) while bases donate hydroxide ions (OH\(^-\)). This typically results in the formation of water and a salt compound.
One classic example of an acid-base reaction involves sodium bicarbonate (NaHCO\(_3\)), an acidic compound, and sodium hydroxide (NaOH), a strong base. When these two substances come into contact, they undergo a neutralization reaction:

• NaHCO\(_3\) + NaOH → Na\(_2\)CO\(_3\) + H\(_2\)O + CO\(_2\)

In this reaction, sodium bicarbonate provides the acidic component while sodium hydroxide supplies the base. Together, they create sodium carbonate, water, and carbon dioxide. Such reactions are essential in various real-world applications, from baking to industrial processes.

Coexisting Compounds

When addressing chemical compounds, the concept of coexisting compounds refers to the ability of two substances to exist together without reacting under normal conditions. This is important in contexts where compound stability is necessary, such as in the storage of chemicals or within human bodies.
In our example, pairs like sodium carbonate (Na\(_2\)CO\(_3\)) and sodium bicarbonate (NaHCO\(_3\)) can exist together in a stable environment. They do not react because they are structurally related forms of carbonate and share enough stability to coexist.

• Coexisting compounds must not force nutrient conversions or involve reactions that destabilize one another.
• This characteristic is often utilized in formulations where multiple substances need to mix without altering each other's properties.

The understanding of which compounds can or cannot coexist informs various scientific and industrial fields to ensure the appropriateness of chemical mixtures.

Sodium Bicarbonate

Sodium bicarbonate (NaHCO\(_3\)), commonly known as baking soda, is a versatile and widely-used chemical. It appears as a fine white powder and is often found in household kitchens, serving as an agent in baking processes.
This compound is slightly basic. It will react with acids forming a salt, water, and carbon dioxide gas, which makes it excellent for cooking applications where it serves as a leavening agent.
In addition to its culinary uses, it plays a significant role in personal hygiene, medicine, and cleaning:

• It can act as an antacid to treat acid indigestion by neutralizing stomach acid.
• It serves as a gentle abrasive in cleaning products, effective at removing tough stains without harsh chemicals.
• Used in medical settings, it helps manage conditions related to acidity and can affect pH balance in physiological contexts.

Understanding sodium bicarbonate's properties is crucial in both everyday life and various scientific settings, recognizing its capability to react, its stability, and its broad spectrum of applications.