Question

Design a separation scheme for Cu2+, Fe3+, Mn2+, and Ni2+ include equations for all reactions.

Answer 1

First dissolve the given mixture of salts and then separate the group (I) cation. here the only one group (I) cation is Cu 2+

First add Aqueous ammonia to the mixture, aq. ammonia reacts with Cu2+ to form a deep blue tetraammine copper(II) complex ion and precipitates out.

Cu2+(aq) + 4NH3(aq) → [Cu(NH3)4] 2+(ppt).

filter out the ppt, thus we separated out Cu2+.

NOW we focus on separation of group (II) cations

The Separation and Confirmation of Group II Ions: Mn2+, Ni2+, Fe3+.

Now take the aqueous soluion of the remaining salt and add one drop of HNO3 in it:

Separation and Confirmation of Mn2+ 1. Place 5 drops of this solution into another clean centrifuge test tube and add a small amount of solid sodium bismuthate (NaBiO3) using a wooden spatula. Use the amount you can fit on the tip of the spatula. 3. Add 20 drops of distilled water, stir, and centrifuge. A purple-colored solution confirms the presence of Mn2+.

The equation for step is: 14H+ (aq) + 2Mn2+(aq) + 5BiO3 – (aq) → 2MnO4 – (aq) + 5Bi3+(aq) + 7H2O(l) purple C.

Separation and Confirmation of Fe3+

1. To the remaining solution from part B above, add 15 drops of 6M NH3·H2O and stir. Centrifuge and decant the supernatant into a clean centrifuge test tube. Label the tube "Nickel" and set it aside for future use. To the precipitate, add 10 drops of 6M hydrochloric acid, stir, and then add 3 drops of 0.1 M NH4SCN. A “blood-red” color confirms the presence of Fe3+. The equations for step 1 are: Fe3+(aq) + 3OH– (aq) → Fe(OH)3(s) Ni2+(aq) + 6NH3(aq) → [Ni(NH3)6] 2+(aq) The equations for step 2 are: Fe(OH)3(s) + 3H+ (aq) → Fe3+(aq) + 3HOH(l) Fe3+(aq) + 6SCN– (aq) → [Fe(NCS)6] 3–(aq) blood-red.

The Confirmation of Ni2+

Add 4 drops of dimethylglyoxime (DMG) to the tube labeled "Nickel" in part C and stir. There is no need to centrifuge, as the nature of the precipitate (sometimes called a “lake”), is more obvious before centrifuging. A strawberry-colored ppt confirms the presence of Ni2+. The equation for step 1 is: [Ni(NH3)6] 2+(aq) + 2H2DMG → [Ni(HDMG)2](s) + 2NH4 + (aq) + 4NH3(aq) pink-red