Question

Qualitative Analysis of Group I Cations: Precipitation and Separation of Group I lons Nam Partner's Name of any) Lab Section MWITH THE Advance Study Assignment 1. The reagent (chemical substance used) to precipitate the all the cations of Group _(symbol and molarity 2. Why do we add an additional drop of the precipitating to the Group I precipitate formed? 3. When we centrifuge why must we use a blank test tube (containing an equal volume of water) on the opposite side of the test tube containing our precipitate? 4. The precipitating reagent was added to a 1 mL sample of the known solution in a test tube. The precipitate that formed was centrifuged and the solution above the precipitate (supernatant) was discarded. Why can we discard supernatant in this step of the experiment? 5. Approximately two mL of dH 0 was added to the precipitate in the test tube above and heated in a boiling water bath, centrifuged and the solution again decanted. It was noticed that the amount of precipitate present was less than what was there before it was heated. What happened to the precipitate? 6. To the white precipitate remaining in the test tube in 5 above, - mL of 6 MNH, was added A color change occurred. What did this mean? 7. How do we confirm the presence or absence of silver ions, Ag?

Answer 1

1. Precipitated by 0.5 M HCl solution.

2. Additional addition of reagent is to confirm the

completion of precipitation. If there is a precipitation

occurring when we add, it means the precipitation is

not complete.

3. The blank on other side is to ensure the smooth

centrifugation. If there is no blank, the apparatus will

jerk and our solution will spill out.

4. We have to do further analysis on the precipitate

only.the group 1 cations will be now converted into

precipitate and the supernatant has no ion now. So we

don't need the supernatant.