ta có:
+)Al2O3 có:54(g)Al=>102(g)Al2O3
20,93% Al có:$\frac{20,93*102}{54}$=39.53% Al2O3(1)
+)28(g)Si=>60(g)SiO2(2)
21,7% Si có:$\frac{21,7*60}{28}$=46,5% SiO2
=>%H2O=100-39.53-46,5=13,97%(3)
từ(1)(2)(3)
=>102x:60y:18z=39.53:46,5:13,97
=>x:y:z=$\frac{39,53}{102}$: $\frac{46,5}{60}$: $\frac{13,97}{18}$
=>x:y:z=0.3:0.7:0.7
=>x:y:z=1:2:2
=>cthh có dạng là:Al2O3.2SiO2.2H2O