Experiment 19: Qualitative Analysis General Chemistry I and II Lab Manual Dakota State University page 198 of 232 approximately 1/4 th the original volume. To this, add ½ mL of concentrated ammonium hydroxide. Check the alkalinity with litmus paper; if it is not alkaline, continue to add concentrated ammonium hydroxide until it is. Once alkaline, add ½ mL of sodium sulfide. The group III ions should precipitate out as sulfides. Centrifuge and decant; the solid is to be tested for group III ions; hold onto the decantate to test for groups IV and V ions. Separation of Ni +2 and Co +2 from Mn +2 , Al +3 and Cr +3 : Add 1 mL of dilute HCl to the precipitate; this should dissolve the nickel and cobalt salts, while leaving the rest as solids. Centrifuge and decant. Verification of Co +2 : To the decantate from the above separation step, add potassium nitrite, KNO 2 , dropwise. If cobalt is present, a yellow precipitate should form. Continue adding potassium nitrite until no further precipitate seems to form. Centrifuge and decant.
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