Question

In basic medium the amount of $Ni^{2+}$ in a solution can be estimated with the dimethylglyoxime reagent. The correct statement(s) about the reaction and the product is(are)

• A. In ammoniacal solution $Ni^{2+}$ salts give cherry-red precipitate of nickel (II) dimethylglyoximate
• B. Two dimethylglyoximate units are bound to one $Ni^{2+}$
• C. In the complex two dimethylglyoximate units are hydrogen bonded to each other
• D. Each dimethylglyoximate unit forms a six-membered chelate ring with $Ni^{2+}$

Answer 1

Answer: (D)

Each dimethylglyoximate unit forms a six-membered chelate ring with $Ni^{2+}$

Answer 2

Estimation of $Ni ^{2+}$ is carried out as. Filtrate of group $III + NH _{4} OH + NH _{4} Cl \stackrel{\Delta}{\longrightarrow}$
passing $H _{2} S$ gas $\rightarrow$ black ppt of NiS. This black ppt of NiS is soluble in conc. $HCl$ in presence of oxidising agent like $KClO _{3}$
$NiS +\underset{ Conc }{2 HCl }+ O \longrightarrow NiCl _{2}+ H _{2} \cdot O + S$
Now this $NiCl _{2}$, in basic medium, treated with dimethyl glyoxime, cherry red ppt of nickel (II) dimethyl glyoximate is obtained, in which two dimethyl glyoximate units are hydrogen bonded to each other and each unit forms a six-membered chelate ring with $Ni ^{2+}$.