Answer:
3.99 moles Al₂O₃
Step-by-step explanation:
The molar mass (g/mol) is used to convert between grams and moles. This value is calculated by taking the individual element molar masses from the periodic table, multiplying them by the corresponding subscripts, then adding them together. Al is 26.98 g/mol and has a subscript of 2. O is 16.00 g/mol and has a subscript of 3. So, the molar mass of Al₂O₃ is 101.96 g/mol.
2(26.98 g/mol) + 3(16.00 g/mol) = 101.96 g/mol
Since it is 101.96 grams PER one mole, the 101.96 is beside grams in the ratio. When setting up the conversion, you want grams in the demoninator (molar mass ratio) to cancel out the grams in the numerator (given value). Since the given number has 3 significant figures, the answer should also have 3 significant figures.
407 grams Al₂O₃ 1 mole Al₂O₃
-------------------------- x -------------------- = 3.99 moles Al₂O₃
101.96 grams