2. 6M acetic acid is added dropwise and stirred to dissolve the precipitate.
3. A few more drops of 6M acetic acid is added until it is acidic. 4. 6 drops of 1M K 2 CrO 4 is added to the solution and stirred. 5. Centrifuged the precipitate when chromate is formed. 6. The supernatant is saved for next procedure D(ii). Procedure D(ii) 1. 10 drops of 1M K 2 C 2 O 4 is added to the solution and stirred for 10 minutes. 2. Centrifuged the precipitate when oxalate is formed. Result
Experiment Observation On adding HCl to the initial sample Mixture White precipitate is formed Unknown 1 No precipitate Unknown 2 No precipitate On adding H 2 S under acidic condition Mixture Turn black and pungent Unknown 1 Clear Unknown 2 Clear On adding H 2 S under basic condition Mixture Black precipitate is formed Unknown 1 No precipitate Unknown 2 No precipitate On adding CO 3 2- Mixture Clear Unknown 1 Clear Unknown 2 Clear On adding CrO 4 2- Unknown 1 No precipitate Unknown 2 No precipitate Metal cations No precipitate On adding C 2 O 4 2- Unknown 1 No precipitate Unknown 2 No precipitate Metal cations No precipitate Discussion
Based on the result, we can predict the solution for the mixture, unknown I and unknown II solutions. Let us begin with the mixture. When the mixture is mix with HCl, a white precipitate is formed. Based on the diagram given in our manual, the precipitate is Ag + ion. The net equation for this reaction is:- Ag + + Cl - AgCl (s) In procedure B, adding of hydrogen sulfide, H 2 S into the solution under acidic condition gives grayish-black precipitate. The solution is made to be acidic in order to prevent the other metal sulfides from other groups to precipitate. Our result for the Procedure B is the solution turns black and pungent, but there is no precipitate formed. But we should see a grey precipitate to confirm the present of copper(II) ion. It might be we missed the precipitate while we observed
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