chemistry molarity

Question

A 10.350 g sample of an unknown hydrate of cobalt(II) bromide is heated until all the water of hydration is removed. The CoBr₂ that remains has a mass of 8.3000 g.

1. How many moles of CoBr₂ are in the sample?____mol
2. How many grams of water were lost in the dehydration______t g
3. How many moles of water were lost?______  (mol) 
4. What is the value of "n" in the formula CoBr2 · n H₂O?______ (1, 2, 3, 4...). 

Answer 1

1). Moles CoBr₂ = 8.3000 g CoBr₂ x 1 mol CoBr₂ / 218.74 g = 0.037945 mols CoBr₂

2). Mass H₂O lost = 10.350 g - 8.3000 g = 2.050 g H₂O lost

3). Moles H₂O lost = 2.050 g H₂O x 1 mol H₂O / 18.02 g = 0.1138 mols H₂O lost

4). n = 3 (see below for explanation)

There are 0.1138 mols H₂O and there are 0.037945 mols CoBr₂. The ratio is 1 mol CoBr₂ : 3 mol H₂O