JEE Main 2022 · 27 July · morning · Single correct · +4 / −1
Given below are two statements.
Statement I: The chlorides of Be and Al have Cl-bridged structure. Both are soluble in organic solvents and act as Lewis bases.
Statement II: Hydroxides of Be and Al dissolve in excess alkali to give beryllate and aluminate ions.
In the light of the above statements, choose the correct answer from the options given below.
- (a) Both Statement I and Statement II are true.
- (b) Both Statement I and Statement II are false.
- (c) Statement I is true but Statement II is false.
- (d) Statement I is false but Statement II is true.
Answer and solution
Answer (d) Statement I is false but Statement II is true.
Solution
Chemistry ma’am · 4 steps
Statement I has one wrong word: these chlorides take electrons, so they are Lewis acids, not bases.
- Statement I first. BeCl₂ and AlCl₃ are covalent, Cl-bridged (polymeric and dimeric Al₂Cl₆) and soluble in organic solvents. All of that is correct.
- Lewis acid or base. Be has only 4 valence electrons around it in BeCl₂, and Al has only 6 in AlCl₃. Both centres are electron deficient, so they accept electron pairs. That makes them Lewis acids, which is why AlCl₃ is used as a catalyst in Friedel-Crafts reactions. Statement I is false.
- Statement II. Both hydroxides are amphoteric and dissolve in excess alkali: Be(OH)₂ + 2OH⁻ → [Be(OH)₄]²⁻ (beryllate) and Al(OH)₃ + OH⁻ → [Al(OH)₄]⁻ (aluminate). Statement II is true.
- So. Statement I is false and Statement II is true, which is option (d).
The idea to keep. Be and Al are diagonal partners: covalent bridged chlorides that act as Lewis acids, and amphoteric hydroxides. In a long statement, check every claim, because one wrong word makes it false.
Answer from the NTA final answer key. Solution by PrepWiser.