I dissolve the Na2SO4, Li2SO4 and NaF in distilled water all at once. However depending on the order in which it is added it completely dissolved or not.
ex) Na2SO4 - Li2SO4 - NaF : Dissolved completely
Li2SO4 - Na2SO4 - NaF : Dissolved completely
NaF - Na2SO4 - Li2SO4 : Not dissolved
NaF - Li2SO4 - Na2SO4 : Not dissolved
I dont know why this reaction is occurs..
Thanks for your help.