Dimethyl glyoxime gives a red precipitate with Ni ²⁺ , which is used for its detection. To get this precipitate readily the best pH range is

Step-by-step solution

Nickel(II) forms a precipitate with the organic compound dimethylglyoxime, C ₄ H ₆( NOH )₂ . The formation of the red chelate occurs quantitatively in a solution in which the 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 pH of the solution from falling below 5 . If the pH does become too low the equilibrium of the above reaction favors the formation of nickel(II)