Hi all,
So with identifying anions and cations, I have a couple questions...
1. With the cation test, do we use FRESH samples each time after we add a reagent to test for a cation? E.g. when adding HCl to the sample to test for Pb2+, and not receiving a precipitate, do you continue to test for the next cation or do you need a completely fresh sample before you continue?
2. Can someone also explain the purpose of adding NH3 during the anion test? Apparently it's to make the solution basic but I don't exactly know why?
Thanks in advance 
Hey!
I don't know why no one's gotten around to answering this but I'll give it my best shot....
1) No you don't need a fresh sample. This is because the anion introduced into the sample ( Cl- wont precipitate with anything in the sample except for Mercury, Silver or Lead. If no precipitate was formed, then you do not need to worry about the Cl- contaminating your sample. In fact , you need to test for lead/silver/mercury first so that you can add sulphate (which precipitates out lead silver mercury barium calcium and strontium), by using the same sample (not a fresh sample) you KNOW that if something precipitates after addition of sulphate, it HAS to be barium, calcium or strontium, essentialy cutting down the potential cations in half!
2) We make the solution basic because some only precipitate inside a certain range of Ph. This is essentially something to do with equilibrium and I cant remember
why but i just know that you have to make the solution basic
I'm sorry if thats not very helpful, but there you go!
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