Two solutions are labeled A and B. Solution A contains Na2CO3 and solution B contains NaHCO3. The two solutions can be distinguished by

On adding MgCl2,Na2CO3 gives precipitate of basic magnesium hydroxide MgCO3.MgOH2 immediately. NaHCO3 do not give any precipitate immediately but on heating gives ppt of normal carbonate MgCO3.  Heat causes bicarbonates to decompose according to the reaction 2HCO3−→CO32−+H2O+CO2Na2CO3.Generation of carbonate ion cause precipitation of the insoluble MgCO3. Phenolphthalein gives pink color with Na2CO3but not with NaHCO3. .