Dimethyl glyoxime gives a red precipitate with Ni^ 2+ , which is...

Nickel(II) forms a precipitate with the organic compound dimethylglyoxime, $\mathrm{C}_4 \mathrm{H}_6(\mathrm{NOH})_2$. The formation of the red chelate occurs quantitatively in a solution in which the $\mathrm{pH}$ is buffered in the range of 5 to 9 . The chelation reaction that occurs is illustrated below.
The reaction is performed in a solution buffered by either an ammonia or citrate buffer to prevent the $\mathrm{pH}$ of the solution from falling below 5 . If the $\mathrm{pH}$ does become too low the equilibrium of the above reaction favors the formation of nickel(II) ion, causing the dissolution of $\mathrm{Ni}(\mathrm{DMG})_2$ back into the mother liquor.