Question

The silicate anion given above in a mineral has $K^{+},C{a}^{2+}$ and $A{l}^{3+}$ cations in 2:1:2. Number of moles of $A{l}^{3+}$ ions per 4 moles of mineral is

Answer 1

Charge on the silicate anion = -10 (from the structure)
Per mol of mineral, 2 mol of $K^{+}$ , 1 mol of $C{a}^{2+}$ and 2 mol of $A{l}^{3+}$ will be there.
Hence, every 4 mol of mineral would have 8 mol of $A{l}^{3+}$ ions.