Presence of Ni(II) ions causes the formation of a red precipitate.
name: Qualitative reaction on Ni(II) ions with dimethylglyoxime is demonstrated.
Qualitative analysis is the determination of the presence of an element in the compounds and mixtures without estimation of its amount. Qualitative reactions are one of the most common tools of qualitative analysis. If the sample under study contains ions specific to the qualitative reaction the release of gas bubbles or precipitate formation or color change is expected. This experiment demonstrates the way to detect Ni2+ ions. Soluble nickel salt solution is used to show qualitative reactions on Ni2+ ions. When soluble nickel salt solution is mixed with dimethylglyoxime ethanol solution it forms a red precipitate of a complex compound - nikel dimethylglyoximate:
Ni2+ + 2C4H8N2O2 → (C4H7O2N2)2Ni + 2H+
Nickel ion is bonded with two molecules of dimethylglyoxime. Each molecule forms two bonds with the metal ion due to two nitrogen atoms. Such ligands as dimethylglyoxime are called bidentate ligands (in the general case - polidentate), since they are able to form two (in general - more) chemical bonds with a metal ion.
Cobalt and other metals also form complexes with dimethylglyoxime, but they are soluble and do not precipitate. This method can be used for quantitative determination of nickel in the presence of cobalt.