Two questions on anion identification (1 Viewer)

[hectic18]

Hello Two questions

1. This is from Conq. Chem, in a table of tests used to identify anions (p214 of latest edition).

Anion: Phosphate
Test: Addition of Mg2+ in ammonia, ammonium nitrate buffer produces a white precipitate of Mg(NH4)PO4.

The given reaction for this test is PO4^3- + Mg2+ + NH4+ --> Mg(NH4)PO4

x_0
How does this equation work? I don't see how there's a 'buffer' in this equation.

2. (also from cc) What anion is present in a solution which produces a precipitate with alkaline BaCl2 but not with an acidic solution of that substance? What is the significance of having the solution as acidic or basic?

Cheers

 

[xiao1985]

q1) with out a buffer, i believe NH4+ will tend to undergo an equilbrium to produce NH3... which means the reaction will not occur

q2) hm.... carbonate?!?!?!?!? since in acidic solution, carbonate react with H+ to produce water and CO2?!?!

 

[hectic18]

q1) with out a buffer, i believe NH4+ will tend to undergo an equilbrium to produce NH3... which means the reaction will not occur

q2) hm.... carbonate?!?!?!?!? since in acidic solution, carbonate react with H+ to produce water and CO2?!?!

Thanks for the help Xiao Q1 seems to make sense now. For q2 I also thought it was carbonate at first xD, but eventually found out that its the test for phosphate.