Question

A shows positive Lassaigne's test for N and its molar mass is 121.
B gives effervescence with aqueous NaHCO3. 
C gives fruity smell. 
Identify A, B, and C from the following.

• A.
• B.
• C.
• D.

Hint:

When solving organic chemistry questions, pay close attention to functional groups and their specific reactions, such as effervescence with NaHCO3 (carboxylic acids) and fruity smells (esters).

Answer 1

The Correct Option is A

To solve this problem, we need to identify the compounds A, B, and C based on the given chemical tests and reactions.

1. Analyzing Compound A:
   • Compound A shows a positive Lassaigne's test for nitrogen, indicating the presence of nitrogen in the compound.
   • The molar mass of A is given as 121.
   • Considering the options, Pyridine (C₅H₅N) is a compound with a molar mass of 79, which does not match. Amides and related structures are likely candidates.
   • Methylamine (CH₃NH₂) has a molar mass of 31, not suitable. Benzamide (C₇H₇NO) has a molar mass of 121 and contains nitrogen, which matches the given data.
2. Analyzing Compound B:
   • Compound B gives effervescence with aqueous NaHCO₃, indicating it is likely a carboxylic acid.
   • Common acids like benzoic acid react with NaHCO₃ to release CO₂ gas, producing effervescence.
3. Analyzing Compound C:
   • Compound C gives a fruity smell, which is characteristic of esters.
   • This suggests that an esterification reaction occurs between the carboxylic acid (Compound B) and an alcohol, forming an ester (Compound C).

Based on the analysis:

• A is Benzamide (C₇H₇NO)
• B is Benzoic Acid (C₇H₆O₂)
• C is an Ester (e.g., ethyl benzoate, C₉H₁₀O₂)

The correct answer corresponds to the option that lists Benzamide as A, Benzoic Acid as B, and an ester as C.

Answer 2

Let’s analyze the given reactions and clues for each compound.

Step 1: Analyzing A:
- A shows positive Lassaigne’s test for nitrogen (N), which means A contains nitrogen.
- The molar mass of A is 121 g/mol.
- Based on the structure options, the compound with a molecular formula that fits these criteria is \(\text{CONH}_2\) (amide group).
This is the structure of \(\text{benzamide}\), which fits the molar mass and the positive Lassaigne’s test for nitrogen.

Step 2: Analyzing B:
- B gives effervescence with aqueous NaHCO3.
This suggests B contains a carboxyl group (-COOH), as carboxylic acids react with NaHCO3 to release carbon dioxide (CO2).
- Therefore, B corresponds to a carboxylic acid group, specifically \(\text{CO}_2\text{H}\), which matches the second compound in the options.
Step 3: Analyzing C:
- C gives a fruity smell, which is characteristic of an ester group.
- The ester functional group in the options is \(\text{CO}_2\text{Et}\) (ethyl ester), which corresponds to the third structure in the options.
Step 4: Final Identification:
- A is \(\text{CONH}_2\) (benzamide), - B is \(\text{CO}_2\text{H}\) (carboxylic acid), - C is \(\text{CO}_2\text{Et}\) (ethyl ester). Thus, the correct answer is Option (1): A = CONH2, B = CO2H, C = CO2Et