Preparing the Known/Unknown Solution 7. Transfer 10 drops of the known/unknown s

Question

Preparing the Known/Unknown Solution 7. Transfer 10 drops of the known/unknown solution into a clean test tu to effect complete 8. dropwise until you see a change in the solution, while stirring Add 6M HCI precipitation. 9, Centrifuge the tube for 1 minute. 10. Add 1 drop of 6M HCl to the mixture. a. if additional precipitate forms, centrifuge the tube for 1 minute. b. Retest the mixture for complete precipitation. discard the supernatant liquid 11. When the precipitation is complete, use a pipette to decant and from the precipitate. tut on 12. Record your observations. w powder s 50 13. Keep the precipitate for the next section. Confirming Lead (l) but 14. Add 2 mL of DI Hizo to the precipitate in the test tube. thi 15. while stirring, heat the tube in a boiling water bath for 3 min. Wh 16, Centrifuge the tube for 1 minute. sectionl 17. Pipette the supernatant liquid into a separate test tube. Keep the precipitate for next 18. Let it supernatant liquid cool in an ice water bath.D nors 19. Add 2-3 drops of 0.1 M Kacro to the cooled supernatant liquid. Sm 3 20. Record your observations. confirming Mercury (hs) 21. Use the precipitate from the previous section. Add 2 ml of 6M NH, to the precipitate: 23. Centrifuge the tube for 1 minute. next section! 24. Pipette the supernatant liquid into a separate test tube. Keep the liquid for the 25. Record your observation of the precipitate. Perc au came grey Confirming Silver 26. Use the supernatant liquid from the previous section. effect complete 27. Add 6M HNO, dropwise until you see a change in the solution, while stirring to precipitation. 28. Record your observations. also Exc hanmue https outlook office comowa svesGetFileAttachment?id-AAMkAGIwOTZIZD... 2/24/2017 services

Explanation / Answer

When treated with dilute HCl. group -I metal ions are precipitated as their chloride.

Pb^2+ + 2Cl- ==> PbCl2 (s) white ppt

Ag+ + Cl - ==> AgCl (s)   white ppt

Hg2^2+ + 2Cl- ==> Hg2Cl2 (s)   white ppt

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Confirming lead:

PbCl2 + K2CrO4 ==> PbCrO4 + 2KCl

                                 yellow solution

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Confirmimg Silver :

Ag+ + NH3 ==> [Ag(NH3)2]^+

[Ag(NH3)2]^+ + HNO3 ==> AgCl + NH4+ + NO3-

Observation : white precipitate initially dissolves but reappears on adding HNO3

Confirming Hg2^2+

Hg2^2+ + 2Nh3 ==> HgNh2Cl==> NH4+ + Cl= + Hg (black ppt)

Observation : black ppt

Confirming lead :

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