Problem 3 - Chemistry in 30 days

Question

ac Which of the following can liberate \(\mathrm{CO}_{2}\) from \(\mathrm{NaHCO}_{3}\) ? (a) Cyclohexanol (b) Phenol (c) 3 -nitrophenol (d) 2, 4, 6 -trinitrophenol

Step-by-Step Solution

Answer

The answer is (d) 2,4,6-trinitrophenol.

Step 1: Identify the Acidity of Compounds

The key to solving this problem is identifying which of the given compounds is acidic enough to liberate carbon dioxide \( (\mathrm{CO}_2) \) from sodium bicarbonate \( (\mathrm{NaHCO}_3) \). Sodium bicarbonate reacts with acids to release \( \mathrm{CO}_2 \), so only a compound with a relatively strong acidic character would cause such a reaction.

Step 2: Compare Acidity of Given Compounds

Cyclohexanol is an alcohol and generally weakly acidic. Phenol is weakly acidic but more so than alcohols because of the resonance stabilization in the phenoxide ion. 3-nitrophenol has an electron-withdrawing nitro group that increases its acidity compared to phenol. 2,4,6-trinitrophenol, or picric acid, has three nitro groups, making it very acidic.

Step 3: Consider the Effective Acids on NaHCO₃

To react with \( \mathrm{NaHCO}_3 \), a compound must have a lower pKa (be more acidic) than carbonic acid \( (\mathrm{H}_2\mathrm{CO}_3) \). Cyclohexanol and phenol are unlikely candidates because they have higher pKa values. 3-nitrophenol is more acidic but may not be strong enough. 2,4,6-trinitrophenol is very acidic due to its three nitro groups, likely acidic enough to liberate \( \mathrm{CO}_2 \) from \( \mathrm{NaHCO}_3 \).

Step 4: Choose the Correct Option

Based on the analysis, 2,4,6-trinitrophenol is the most acidic compound among the options, due to its multiple nitro groups, making it likely to react with \( \mathrm{NaHCO}_3 \) and release \( \mathrm{CO}_2 \). Therefore, the correct answer is (d) 2,4,6-trinitrophenol.

Key Concepts

Sodium Bicarbonate Reactions

Sodium bicarbonate, commonly known as baking soda, is a chemical compound with the formula \( \text{NaHCO}_3 \). It is commonly used in baking, cleaning, and neutralizing acids. Sodium bicarbonate is known for its ability to react with acidic compounds to release carbon dioxide gas \( (\text{CO}_2) \), a process that is often seen when baking soda is used in recipes to help dough rise.

When sodium bicarbonate reacts with an acid, the acid donates a proton to the bicarbonate ion \((\text{HCO}_3^- )\), forming carbonic acid \((\text{H}_2\text{CO}_3)\). This carbonic acid is unstable and quickly decomposes into water \((\text{H}_2\text{O})\) and carbon dioxide \((\text{CO}_2)\) gas. This reaction is a clear demonstration of how acids and bases react to form new products, highlighting the importance of understanding chemical reactions in acid-base chemistry.

Carbon Dioxide Liberation

The liberation of carbon dioxide \((\text{CO}_2)\) is a key element in various biochemical and industrial processes. When sodium bicarbonate \((\text{NaHCO}_3)\) reacts with an acid, carbon dioxide is released as one of the main products. The reaction can be simplified as follows:

\[ \text{NaHCO}_3 + \text{H}^+ \rightarrow \text{Na}^+ + \text{H}_2\text{O} + \text{CO}_2 \]

This reaction is exploited in baking, where the carbon dioxide gas helps dough or batter to rise, creating a light and fluffy texture in baked goods.

• The key to effective \(\text{CO}_2\) liberation lies in the use of a sufficiently acidic substance.
• An acid with enough strength will readily donate a proton to the sodium bicarbonate, leading to the formation of carbon dioxide gas.