1. Separation and Identification of Bismuth and Tin Ions Experiment 6 Qualitative Analysis

2. Objective/Goal To separate out Bismuth and Tin ions based on _____________ To analyze the separated portions of the unknown to identify whether tin, bismuth, or tin and bismuth are present in the unknown

3. Basic Premise of Separation and Identification Bismuth (Bi 3+ ) and tin (Sn 4+ ) ions belong to the group __ cations known as the ________ group. They are small in size but carry a high charge, so they act as _____ by pulling the hydroxide away from water. They precipitate in the presence of ______ and they stay as ions in solution at ________ pH. Sn 2+ instantly reduces Bi 3+ to Bi 0.

4. The Reactions

5. T.I.1 To get a complete separation of tin from bismuth, it is necessary to have tin present as Sn 4+, because both tin(II) and bismuth(III) _________________ as hydroxides: Bi(OH) 3 and Sn(OH) 2. Bi 3+ + 3 OH 1- → Bi(OH) 3 (wh ppt)T.I.1 (+ NaOH) Sn 2+ + 2 OH 1- → Sn(OH) 2 (wh ppt)T.I.5 (SnCl 2 + NaOH) Precipitate forms, and then re-dissolves as more NaOH is added

6. Separations (T.I.2-3) In basic solution (6M NaOH, T1.1), bismuth is in ______ form and tin will remain dissolved Centrifugation- use of centrifugal force to separate items based on their _______________ Will be used to separate ____________ from _______ (called “supernatant”) Will allow us to look at each ion separately It is critical to remove ALL of the _____________ from the precipitate pellet without taking the _____ as part of the supernatant. Therefore, it is necessary to wash the pellet with di H 2 O and recentrifuge after removing the supernatant

7. T.I.5 There is no complete agreement on the composition of Sn 2+ ion; it could be SnO 2 2- or Sn(OH) 4 2- or Sn(OH) 3 1- or HSnO 2 1- or all four ions at once: Sn(OH) 2 + 2 OH 1- → Sn(OH) 4 2- (amphoteric) or Sn(OH) 2 + 2 OH 1- → SnO 2 2- + 2 H 2 O (amphoteric)

8. T.I.5 cont’d. Upon contact with air Sn 2+ ions are _______ to Sn 4+ [Sn(OH) 6 2- ], so the reagent for the previous reaction is prepared fresh during the procedure. 2 Sn(OH) 4 2- + O 2 + 2 H 2 O → 2 Sn(OH) 6 2- It also reacts with itself as follows: 2 Sn(OH) 4 2- → Sn + Sn(OH) 6 2- + 2 OH 1- If acid is added: Sn(OH) 2 + 2 H + → Sn 2+ + 2 H 2 O

9. The following reaction is used to identify both ions and occurs instantly: (T.I.6 & T.II.10) 2 Bi(OH) 3(s) + 3 SnO 2 2- + 3 H 2 O → 2 Bi (s) (bk ppt) + 3 SnO 2+ + 12 OH 1- or 3 Sn(OH) 4 2- + 2 Bi(OH) 3 → 2 Bi (s) (bk ppt) + 3 Sn(OH) 6 2-

10. T.II.1 Sn 4+ + 6 Cl 1- ↔ SnCl 6 2 - (+ HCl)

11. T.II.2 2 Zn 0 + Sn 4+ → 2 Zn 2+ + Sn 0 2x Zn 0 → Zn 2+ + 2 e - oxidation 4 e - + Sn 4+ → Sn 0 reduction

12. T.II.3 Excess ____ reacts with ________ to form hydrogen gas Zn + 2 H + → Zn 2+ + H 2

13. T.II.5 If a solution containing Bi/Sn is diluted with __________, a milky-white suspension may result, because of the formation (by hydrolysis) of the insoluble white basic salts of Bi (after adding Zn, but before HCl) Bi 3+ + Cl 1- +H 2 O ↔ BiOCl + 2 H + If the milky suspension is treated with ___, the milky ness disappears, because the equilibrium is shifted to the _______.

14. T.II.6 Sn is less active than Zn and does not react with HCl until all zinc reacts or excess is removed; after that Sn reacts with HCl to form Sn 2+ Sn + 2 H + → Sn 2+ + H 2

15. T.II.8-10 Sn 2+ can be oxidized to Sn 4+ by oxygen in the air, so confirmation test should be done ASAP.