# How do you write the formula for the following compounds: Barium chloride dihydrate and Sodium sulfite heptahydrate?

$B a C {l}_{2} \cdot 2 {H}_{2} O$, and $N {a}_{2} S {O}_{3} \cdot 7 {H}_{2} O$
$\text{Hydrate}$ refers to a $\text{water of crystallization}$. $\text{Sulfite}$ refers to the $S {O}_{3}^{2 -}$ counterion. When these material crystallize from water as their metal salts, the salt picks up several water molecules that are included in the solid state structure, the crystal (hence $\text{a water of crystallization}$).