Chemistry · Oct / Nov 2025 · Paper 11 · Question 8

Aluminium ions, Al$^{3+}$, react with sulfate ions, SO$_4^{2-}$, to form aluminium sulfate. Which row shows the correct empirical formula and ionic formula of aluminium sulfate?

1. Aempirical formula: AlSO$_4$; ionic formula: Al$^{3+}$SO$_4^{2-}$
2. Bempirical formula: Al$_2$S$_2$O$_8$; ionic formula: Al$^{3+}$(SO$_4^{2-}$)$_2$
3. Cempirical formula: Al$_2$S$_3$O$_{12}$; ionic formula: Al$^{3+}$$_2$(SO$_4$)$^{2-}$$_3$
4. Dempirical formula: Al$_3$S$_2$O$_8$; ionic formula: Al$^{2+}$$_3$(SO$_4^{3-}$)$_2$

As printed in the paper