The formula unit mass of aluminum carbonate is _____. 

Carbonate is CO3 with a -2 charge and, Aluminum has a +3 charge 
On combining them it would be Al2(CO3)3, meaning that the compound ha: 
2 total Aluminums 
3 total carbons 
9 total Oxygen 
Now, the mass of Aluminum (2×27= 54 amu) 
mass of Carbon(3×12 = 36 amu) 
And, the mass of Oxygen (9×16 = 144 amu) 
Therefore, sum of all masses (Al+C+O) = 54+36+144 = 234 amu 
Thus, 234 grams exist in 1 Mole of Aluminum Carbonate.