OK, so they give me a solution containing 2 anions and 2 cations. They tell me to add NaOH. (I get an off-white precipitate, so one of the cations is Mn2+)
They then tell me to filter the mixture (solution + NaOH), and add dilute HNO3 to the filtrate, drop by drop. What is this test for?
In the answer scheme, you are supposed to get a white precipitate that forms and re-dissolves, and hence deduce that the other cation could be Zn2+, Pb2+, or Al3+. But I don't get how we could come to that and what's the theory behind that. :/
Any help would be greatly appreciated!
They then tell me to filter the mixture (solution + NaOH), and add dilute HNO3 to the filtrate, drop by drop. What is this test for?
In the answer scheme, you are supposed to get a white precipitate that forms and re-dissolves, and hence deduce that the other cation could be Zn2+, Pb2+, or Al3+. But I don't get how we could come to that and what's the theory behind that. :/
Any help would be greatly appreciated!
-
THe "answer scheme" isnt the answer..it just tells you what happens and what to deduce when you do this or that. When you add NaOH you are testing for cations. If you got a white ppt(precipitate) that forms and re-dissolved in excess NaOH, the cation could be ZN2+, Al3+ or Pb2+. when you add NaOH it reacts with the unknowen salt to cause the unknown salt to form its hydroxide. the Hydroxides of lead, zinc and aluminum are soluble in excess NaOH
However, you got an off-white precipitate that did not re-dissolve, so yes you can deduce tht one of the cations is Mn2+. (the solution was coloured right? slightly pink if anything)
You add Dilute HNO3 to test for anions...not cations...but you usually add something after adding HNO3.....and adding dilute acid to a solution conatining NaOH makes no sense..they will just r eact... so I have no idea what you are testing for....maybe you are testing your patience XD lol
However, you got an off-white precipitate that did not re-dissolve, so yes you can deduce tht one of the cations is Mn2+. (the solution was coloured right? slightly pink if anything)
You add Dilute HNO3 to test for anions...not cations...but you usually add something after adding HNO3.....and adding dilute acid to a solution conatining NaOH makes no sense..they will just r eact... so I have no idea what you are testing for....maybe you are testing your patience XD lol