Question

calculate formula unit mass Al (oH) 3

Answer 1

You add up the molar masses of each atom, in this case 1 Al, 3 O, and 3 H.  Using a periodic table or datasheet, Al = 26.9815, O = 15.9994, and H = 1.0078.
Adding up gives (26.9815)+3(15.9994)+3(1.0078)=78.0031gmol


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