Cations 3

• The cations of Group III are precipitated in a solution containing ammonia, ammonium chloride, ammonium sulfide
• The group precipitate is a mixture of sulfides and hydroxides
• The high concentration of sulfide ion necessary for precipitation of Group III sulfides is obtained in an ammoniacal solution. This basic solution also produces the precipitation of chromium and aluminum as hydroxides in Group III
• Chromium, zinc, and aluminum hydroxides dissolve in excess KOH solution to form a soluble group
• Manganese, iron, nickel, and cobalt hydroxides precipitate to form an insoluble group
• For the first step, separate group 3 from other cations. Ammonium chloride, ammonia and thioacetamide solution are used as precipitating agent
• For the second step, dissolve everything back in solution using dilute hydrochloric acid. Copper sulfide and Nickel sulfide will remain undissolved, so use nitric acid
• For the third step, separate group 3 into subgroups using sodium peroxide and potassium hydroxide
• Use saturated ammonium acetate and dilute acetic acid as the precipitating agent to separate aluminum ions from the zinc and chromic ions
• For confirmation of aluminum ions, use Aluminon, the triammonium salt of aurintricarboxylic acid, a dye. Cranberry red/pink precipitate will show if positive
• To separate zinc and chromate ions, use barium acetate
• For confirmation of chromate ions, use hydrochloric acid to dissolve the precipitate and separate the barium sulfate. Hydrogen peroxide to form blue colored perchromate
• If chromate ion is positive, it will show a blue color that fades rapidly
• For confirmation of zinc ions, use Dilute acetic acid to neutralize ammonia, leaving the zinc ions free. And use Hydrogen sulfide from thioacetamide giving white precipitate
• For the third day, Addition of hydrochloric acid to dissolve the hydroxide precipitates to make ions in free state
• For confirmation of manganese ion, use sodium bismuthate as the reagent. If positive, it will show a reddish-purple color in supernatant liquid
• For ferric ion, use ammonium thiocyanate as the reagent. If positive, there will be an appearance of deep red coloration
• For confirmation of cobalt ion, use alcoholic ammonium thiocyanate. If positive, appearance of blue-green color at the junction of the 2 liquids
• For confirmation of nickel ion, use ammonia and dimethylglyoxime as the reagent. If positive, there will be formation of a red precipitate