JEE Main 2023 · 30 January · evening · Single correct · +4 / −1
Chlorides of which metal are soluble in organic solvents :
- (a) K
- (b) Be
- (c) Ca
- (d) Mg
Answer and solution
Answer (b) Be
Solution
Chemistry ma’am · 3 steps
Tiny Be²⁺ pulls the chloride's electron cloud so hard that BeCl₂ turns covalent.
- What dissolves where. Ionic solids dissolve in water, which stabilises the separated ions. Covalent molecules dissolve in non-polar organic solvents. So we need the chloride with the most covalent character.
- Fajans' rules. A small, highly charged cation polarises the anion strongly, and that makes the bond covalent. Be²⁺ is the smallest cation here and carries a +2 charge, so its polarising power is the highest.
Chloride Cation Polarising power Bond character KCl large, +1 very low ionic BeCl₂ very small, +2 very high covalent MgCl₂ small, +2 moderate mainly ionic CaCl₂ larger, +2 low ionic - So. BeCl₂ is covalent and dissolves in organic solvents, so the answer is (b) Be. This is one of the anomalous properties of beryllium.
The idea to keep. Small cation, high charge, high polarising power, covalent bond: that chloride dissolves in organic solvents. Be and Li break the pattern of their groups for exactly this reason.
Answer from the NTA final answer key. Solution by PrepWiser.