Question

Identify the incorrect statement about the group 13 elements

• A. Nature of aqueous solution of borax is alkaline
• B. Orthoboric acid is a weak tribasic acid
• C. Metaboric acid on heating gives an acidic oxide
• D. LiBH\(_4\) acts as a reducing agent

Hint:

Key properties of Boron compounds: Borax (Na\(_2\)B\(_4\)O\(_7\)):} Aqueous solution is alkaline due to hydrolysis. Orthoboric acid (H\(_3\)BO\(_3\)):} A weak monobasic} Lewis acid, not a Brønsted acid. Boron oxides (e.g., B\(_2\)O\(_3\)):} Acidic in nature. Metal borohydrides (e.g., LiBH\(_4\)):} Strong reducing agents.

Answer 1

The Correct Option is B

Let's analyze each statement regarding Group 13 elements:
Statement 1: Nature of aqueous solution of borax is alkaline.
Borax (sodium tetraborate decahydrate, \( \text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O} \)) dissolves in water and undergoes hydrolysis. The hydrolysis products are boric acid (\( \text{H}_3\text{BO}_3 \), a weak acid) and sodium hydroxide (\( \text{NaOH} \), a strong base).
\[ \text{Na}_2\text{B}_4\text{O}_7 + 7\text{H}_2\text{O} \rightleftharpoons 2\text{NaOH} + 4\text{H}_3\text{BO}_3 \]
Since a strong base (\( \text{NaOH} \)) and a weak acid (\( \text{H}_3\text{BO}_3 \)) are formed, the solution will be basic (alkaline). This statement is correct.
Statement 2: Orthoboric acid is a weak tribasic acid.
Orthoboric acid is \( \text{H}_3\text{BO}_3 \) (or \( \text{B}(\text{OH})_3 \)). It is a weak acid. However, it is not a Brønsted acid (proton donor) but rather a Lewis acid, accepting a hydroxide ion from water, thereby releasing a proton from water:
\[ \text{B}(\text{OH})_3 + \text{H}_2\text{O} \rightleftharpoons [\text{B}(\text{OH})_4]^- + \text{H}^+ \]
Since one molecule of orthoboric acid generates only one \( \text{H}^+ \) ion per molecule in aqueous solution, it is a monobasic acid. Therefore, the statement that it is a tribasic acid is incorrect.
Statement 3: Metaboric acid on heating gives an acidic oxide.
Metaboric acid (\( \text{HBO}_2 \)) is an intermediate formed during the heating of orthoboric acid. On further strong heating, metaboric acid undergoes dehydration to form boron trioxide (\( \text{B}_2\text{O}_3 \)).
\[ 2\text{HBO}_2 \xrightarrow{\text{heat}} \text{B}_2\text{O}_3 + \text{H}_2\text{O} \]
Boron trioxide (\( \text{B}_2\text{O}_3 \)) is an acidic oxide, meaning it reacts with bases to form borates. This statement is correct.
Statement 4: LiBH\(_4\) acts as a reducing agent.
Lithium borohydride (\( \text{LiBH}_4 \)) is a well-known and powerful reducing agent commonly used in organic synthesis. It can reduce various functional groups, including aldehydes, ketones, esters, and carboxylic acids. This statement is correct.
Conclusion:
Based on the analysis, the incorrect statement is Statement 2.
The final answer is \( \boxed{\text{Orthoboric acid is a weak tribasic acid}} \).