Mg3N2(s) + 6H2O(l) -> 3Mg(OH)2(s) + 2NH3(g)

Question

a. How many grams of H2O are needed to produce 40g of Mg(OH)2?

Answer 1

First, you want to make sure that your equation is balanced. Since it looks like it is, you can move on to setting up the formulas.

In order to obtain 40g of Mg(OH)2, you need the molecular mass for magnesium hydroxide (58.3 g/mol).

So, from 40g Mg(OH)2 you need to get to moles of Mg(OH)2. Once you have moles, you use the molar ratio based on the balanced reaction equation. In this case, there are 6 moles of H2O per 3 moles of Mg(OH)2. Once you have moles of H2O, you can convert to grams by using the molecular mass of water (18 g/mol)

Does this help?