The denticity of the ligand present in the Fehling's reagent is ___________.

Solution

Chemistry ma’am · 3 steps

Fehling's ligand is tartrate. Count its oxygen atoms that actually reach the copper ion.

1. Find the ligand. Fehling's A is copper sulphate solution. Fehling's B is alkaline sodium potassium tartrate (Rochelle salt). When they are mixed, the tartrate ion C₄H₄O₆²⁻ wraps around Cu²⁺ and keeps it from precipitating as Cu(OH)₂.

   ⁻OOC-CH(OH)-CH(OH)-COO⁻

2. Count donor atoms. Each of the two carboxylate groups binds through one oxygen, which gives 2. Each of the two hydroxyl groups also binds through its oxygen, which gives 2 more. Both hydroxyl groups lose their proton in the strongly alkaline solution.
3. So. Tartrate binds through 2 + 2 oxygen atoms, so its denticity is 4.

The common slip: 2. Counting only the two carboxylate groups gives 2. The two hydroxyl oxygens also bind to copper.

The idea to keep. Denticity counts donor atoms, not groups. In a polyfunctional ligand, check every group, both carboxylate and hydroxyl, that can reach the metal.

Answer from the NTA final answer key. Solution by PrepWiser.