Calculating Consentration Molarity?

Question

A solution is prepared by dissolving 13.2 grams of Ba(OH)2* 8 H2O in 275 mL of aqueous solution. Ba(OH)2* 8 H2O is water soluble and is a strong electrolyte. Calculate the OH- (aq) concentration (molarity) in the resulting solution.

Please explain how you do it. Thank you.

Answer 1

Formula mass of Ba(OH)2*8H2O(octahydrate) 315.46 g/mol.
13.2 grams of Ba(OH)2*8H2O <==> 13.2/315.46 = 0.0418 (mole)
0.0418 mole in 275 mL <==> 0.0418/0.275 = 0.163 M (of Ba(OH)2)
[OH] = 2*0.163 M = 0.326M