Question

State Kohlrausch's law of independent migration of ions. With the help of a curve, explain why it is not easy to determine $\mathrm{\Lambda^\circ_m}$ for weak electrolytes by extrapolating the concentration – molar conductivity curve, as it is for strong electrolytes.

Hint:

Limiting molar conductivity = sum of ion contributions; weak electrolytes give a steep, non-extrapolatable curve.

Answer 1

(i) answer: An ambidentate ligand is a ligand that has two different atoms able to donate a lone pair to the metal, but it can use only one of them at a time. So depending on which atom it bonds through, you get a slightly different complex. A good example is the nitrite ion $\mathrm{NO_2^-}$. It can join the metal through its nitrogen atom, and then we call it 'nitro', or it can join through one of its oxygen atoms, and then we call it 'nitrito'. Same ion, two possible donor atoms, only one used at a time. That is what makes it ambidentate.

(ii) answer: A double salt is a salt that exists as a single solid crystal when dry, but the moment you dissolve it in water it breaks up completely into all the simple ions it was made from. In other words, in solution it loses its own identity and behaves just like a plain mixture of its parts. A common example is Mohr's salt, $\mathrm{FeSO_4 \cdot (NH_4)_2SO_4 \cdot 6H_2O}$. In water it gives free $\mathrm{Fe^{2+}}$, $\mathrm{NH_4^+}$ and $\mathrm{SO_4^{2-}}$ ions, exactly the ions you would expect from its parts. This is different from a complex, which keeps its complex ion intact in solution.