Problem 73 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

Which of the following gives effervescenes of \(\mathrm{CO}_{2}\) with \(\mathrm{NaHCO}_{3}\) solution? (a) \(\mathrm{HCOOH}\) (b) \(2,4,6\) -trinitrophenol (c) Both (a) and (b) (d) None of these

Step-by-Step Solution

Answer

Option (c) Both (a) and (b) give effervescence with \( \mathrm{NaHCO}_{3} \).

Step 1: Understanding Effervescence

Effervescence is the escape of gas from an aqueous solution and the formation of bubbles. In this problem, we're looking for a reaction that releases carbon dioxide \( \mathrm{CO}_{2} \) gas when a substance reacts with \( \mathrm{NaHCO}_{3} \). This usually occurs when an acid reacts with \( \mathrm{NaHCO}_{3} \), as bicarbonate ions \( \mathrm{HCO}_{3}^{-} \) react with hydrogen ions \( \mathrm{H}^{+} \), forming \( \mathrm{CO}_{2} \) gas and water \( \mathrm{H}_{2} \mathrm{O} \).

Step 2: Analyzing Option (a)

Formic acid, \( \mathrm{HCOOH} \), is a simple carboxylic acid. When it reacts with sodium bicarbonate \( \mathrm{NaHCO}_{3} \), it will produce carbon dioxide. The reaction is: \[ \mathrm{HCOOH} + \mathrm{NaHCO}_{3} \rightarrow \mathrm{CO}_{2} \uparrow + \mathrm{H}_{2}\mathrm{O} + \mathrm{Na}^{+} + \mathrm{HCOO}^{-} \]This reaction releases \( \mathrm{CO}_{2} \) as effervescence.

Step 3: Analyzing Option (b)

2,4,6-Trinitrophenol, known as picric acid, is a stronger acid than formic acid and can also react with \( \mathrm{NaHCO}_{3} \) to release carbon dioxide gas. The general reaction with an acid is:\[ \mathrm{C_6H_2(NO_2)_3OH} + \mathrm{NaHCO}_{3} \rightarrow \mathrm{CO}_{2} \uparrow + \mathrm{H}_{2}\mathrm{O} + \mathrm{Na}^{+} + \text{other products} \]This confirms effervescence will be seen.

Step 4: Concluding the Solution

Since both formic acid \( \mathrm{HCOOH} \) and 2,4,6-trinitrophenol react with \( \mathrm{NaHCO}_{3} \) to produce carbon dioxide, both substances will cause effervescence. Therefore, both options (a) and (b) result in effervescence.

Key Concepts

Acid-Base Reactions

Acid-base reactions are fundamental concepts in chemistry where acids and bases interact to form salt and water. Their importance extends to understanding effervescence, especially involving bicarbonate reactions. In this exercise, when formic acid (HCOOH) or 2,4,6-trinitrophenol reacts with sodium bicarbonate (NaHCO₃), an acid-base reaction occurs. The hydrogen ions (H⁺) from the acid react with the bicarbonate ions (HCO₃⁻) to produce carbon dioxide gas (CO₂), water (H₂O), and other ionic products.

These reactions can be described generally as:

• Acid (HA) + NaHCO₃ → CO₂ (gas) + H₂O + Na⁺ + A⁻

In this type of reaction, the release of CO₂ gas is what causes the observable bubbles, which are an indicator of the reaction taking place. Understanding how acids donate protons to bases helps us anticipate these kinds of reactions.
Recognizing the nature of acids, such as formic acid and trinitrophenol, enhances comprehension of chemical behavior and reaction prediction in various practical scenarios.

Effervescence in Chemistry

Effervescence is a visual evidence of chemical reactions where gases escape from a liquid, forming bubbles. This is commonly seen during acid-base reactions, particularly with carbonates and bicarbonates. The term applies broadly to reactions where gases like carbon dioxide are released, resulting in a fizzing or bubbling effect.

In this context, when formic acid or 2,4,6-trinitrophenol is introduced to a sodium bicarbonate solution, the substrate reacts to release CO₂ gas, which manifests as effervescence. This gas formation is a direct result of the decomposition of bicarbonate ions by an acid, a typical acid-base reaction.
Key points to remember about effervescence include:

• Involves the escape of gas from a solution.
• Commonly associated with acids reacting with carbonates and bicarbonates.
• Provides a practical visual cue for identifying reactions.

Effervescence not only provides insight into the dynamics of reaction mechanisms but also serves as a practical tool for qualitative analysis in laboratory settings.

Carboxylic Acids

Carboxylic acids are organic compounds containing a carboxyl group (COOH). They are characterized by their acidity, which is largely attributed to the ability of the carboxyl group to donate a hydrogen ion (H⁺) in solution. Carboxylic acids, like formic acid, are known for their reactivity with bicarbonates, inducing effervescence.

Formic acid, the simplest carboxylic acid, is a clear example of acidity facilitating the release of CO₂ when reacting with sodium bicarbonate. The reaction can be illustrated as follows:\[\text{HCOOH} + \text{NaHCO}_3 \rightarrow \text{CO}_2 \uparrow + \text{H}_2\text{O} + \text{Na}^+ + \text{HCOO}^-\]Carboxylic acids are vital in many biological processes and industrial applications. Understanding how these compounds behave assists in predicting their interaction in various chemical systems.
It's also crucial to note that while all carboxylic acids possess the potential to engage in similar reactions, their strength varies, affecting their reactivity and the vigor of effervescence produced.