what is mass of 0.65 moles of Mg(OH)2?

Question

What is its mass?

Answer 1

Find the molecular weight of Mg(OH)₂ in grams per mole, and multiply it by the number of moles of Mg(OH)₂.  That will give the mass in grams of Mg(OH)₂.

 

Look up in your chemistry book the atomic weights in grams/mole of Mg, O, and H.  The molecular weight (W) of Mg(OH)₂ is the sum of the atomic weights:

 

W = (Mg) + 2(O) + 2(H)

 

The mass in grams (m) is

 

m = W x (the number of moles) = W x (0.65 moles)

 

Look up the atomic weights, and just plug in the numbers. 

 

 

Answer 2

Take the number of moles and multiply it by the molar mass.  You get the molar mass by adding the molar masses of each atom in the compound.  Notice that there are 5 atoms.

 

Mg = 24.31g

O = 16.00g

O = 16.00g

H = 1.01g

H = 1.01g

 

Adding these together gives a molar mass of 58.33g.  What do you get when you multiply it by 0.65 moles?