## Chemistry: A Molecular Approach (3rd Edition)

Its formula is $K_{2}CO_{3}.2H_{2}O$
The cation of potassium carbonate dihydrate is $K^{+}$. The anion is carbonate, i.e $CO_{3}^{2-}$. To balance the charges, 1 $CO_{3}^{2-}$ combines with 2 $K^{+}$. Then it also has 2 (di) water molecules of hydration. So, its formula is $K_{2}CO_{3}.2H_{2}O$.