Question

How many moles of H atoms are there in 21.66 g of Mg(OH)2?


What is the mass of F (in g) in 8.03 x 1023 BF3 molecules

Answer 1

mol Mg(OH)2 = grams/molar mass = 21.66g/molar mass.
There are twice as many mols of H atoms since there are two H atoms/molecule Mg(OH)2.

mols BF3 = 8.63E23/6.02E23 = ?
There are 3x as many F mols.
Then g = mols x atomic mass.

Answer 2

but how do you set them up?

Answer 3

You mean like this? You should be able to take what I first gave you and set it up as below.
21.66 g Mg(OH)2 x [1 mol Mg(OH)2/molar mass Mg(OH)2] x [2 mol H atoms/1 mol Mg(OH)2] =
21.66 x (1/58.32) x (2/1) = mols H atoms.