Separation of Copper as CuS and Estimation of Zinc Gravimetrically as ZnNH4PO4

Estimation of Zn from the mixture of Zn and Cu solution
Procedure:

  • Transfer 25 mL of, supplied solution with a pipette into a 250 mL beaker.
  •  Acidify the solution with 1-2 mL of cone. HCl and warm the solution and then pass H2 S carefully to precipitate (ppt) copper sulphide completely.
  •  Filter off the ppt and wash the ppt with water several times to remove the adhering Zn2+.
  •  Collect the washing with filtrate and test again by passing H2 S through the solution. If there is any precipitate, repeat the process until the solution is completely free from Cu2+
  •  Remove H2 S by carefully boiling the solution (test with lead acetate paper). Adjust the volume of the solution to about 125-130 mL.
  •  Neutralize the filtrate with NH4 OH solution using methyl red as an indicator.Add about 4-5 g of solid NH4 Cl and 10 mL  of 2N sodium acetate solution.
  •  Heat on a water bath and when it becomes hot, add 10 mL of 10% diammonium hydrogen phosphate solution slowly from a pipette or burette in it.
  •  Heat on a water bath for 1 hour in a covered beaker, filter through a previously weighed sintered glass crucible, wash several times using a total volume of approximately 150 mL of cold water (test the last washing for chloride of phosphate ion) and finally wash with 5 mL rectified spirit.
  •  Dry to constant weight at 105 0 C, weigh as ZnNH4 PO4.

1g ZnNH4 PO4 = 0.3665 g Zn

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This article was posted by
Md. Ataur Rahman
3rd Year B.Sc.(Hons)
Depart. Of Chemistry
RU



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