Answer
(a) $287.91\text{ g/mol}$
(b) $231.53\text{ g/mol}$
(c) $209.94\text{ g/mol}$
(d) $537.49\text{ g/mol}$
(e) $222.84\text{ g/mol}$
Work Step by Step
(a) $CaWO_{4}$
(scheelite, an ore of tungsten)$ = 40.078+183.84+4(15.999)\approx 287.91\text{ g/mol}$
(b) $Fe_{3}O_{4}$
(magnetite) $= 3(55.845)+4(15.999) \approx 231.53\text{ g/mol}$
(c) $Na_{3}AlF_{6}$
(cryolite) $= 3(22.989)+26.982+6(18.998)\approx 209.94\text{ g/mol}$
(d) $Be_{3}Al_{2}Si_{6}O_{18}$
(beryl) $=3(9.0122)+2(26.982)+6(28.085)+18(15.999)\approx 537.49\text{ g/mol}$
(e) $Zn_{2}SiO_{4}$ (willemite)$ =2(65.38)+28.085+4(15.999)\approx 222.84\text{ g/mol}$
