What mass of ammonium thiocyanate must be used if it is to react completely with 6.5 g barium hydroxide octahydrate?

The reaction equation is:
Ba(OH)₂*8H₂O + 2NH₄SCN(s) → Ba(SCN)₂(s) + 10H₂O(l) + 2NH₃ (g)

The molecular mass of barium hydroxide octahydrate is 315 grams /mol.
We determine the number of moles of barium hydroxide octahydrate:
moles = mass / Mr
moles = 6.5 / 315
moles = 0.02 mol

Using the equation, we can determine that the moles of ammonium thiocyanate required are:
2 * 0.02 = 0.04 mol

The molecular weight of ammonium thiocyanate is 76.1 grams / mol

Weight = moles * Mr
Weight = 0.04 * 76.1
Weight = 3.04 grams

3.04 grams of ammonium thicyanate are required.