Final answer:
There are 3.96 moles of oxygen molecules in a sample of magnesium phosphate that contains 72 g of magnesium, based on the calculation involving the molar mass of magnesium and the ratio of magnesium to oxygen in magnesium phosphate.
Step-by-step explanation:
To calculate the number of moles of oxygen molecules in a sample of magnesium phosphate (Mg3(PO4)2) that contains 72 g of magnesium, we need to first determine the molar mass of magnesium and then the molar mass of magnesium phosphate to find the mass ratio.
The molar mass of magnesium (Mg) is approximately 24.31 g/mol. Since the sample contains 72 g of Mg, we can calculate the number of moles of Mg using the formula:
moles of Mg = mass of Mg / molar mass of Mg
moles of Mg = 72 g / 24.31 g/mol = 2.96 moles
In the magnesium phosphate molecule, for every 3 moles of Mg, there are 8 moles of oxygen atoms, as indicated by the subscript in the formula (PO4 is one phosphorus and four oxygen atoms, and there are two PO4 groups).
So, if there are 2.96 moles of Mg, the corresponding moles of oxygen atoms can be calculated as:
moles of O = (2.96 moles Mg x 8 moles O / 3 moles Mg)
moles of O = 7.92 moles
However, O2 is the molecular form of oxygen and contains 2 atoms. Therefore, to find the moles of O2 molecules, we divide the moles of oxygen atoms by 2:
moles of O2 = moles of O / 2 = 7.92 moles / 2 = 3.96 moles
Thus, there are 3.96 moles of oxygen molecules in the sample.