Answer:
To find the molecular formula, we need to determine the empirical formula and then use the molar mass to calculate the molecular formula.
Determine the empirical formula:
Find the number of moles of each element:
Moles of chromium = 0.70 g / 52.00 g/mol = 0.0135 mol
Moles of sulfur = 0.65 g / 32.06 g/mol = 0.0203 mol
Moles of oxygen = (2.65 g - 0.70 g - 0.65 g) / 16.00 g/mol = 0.0681 mol
Divide each mole value by the smallest one (0.0135 mol) to obtain the empirical formula:
Chromium: 0.0135 mol / 0.0135 mol = 1
Sulfur: 0.0203 mol / 0.0135 mol = 1.50 (rounded to 2)
Oxygen: 0.0681 mol / 0.0135 mol = 5 (rounded to 4)
The empirical formula is CrSO4.
Calculate the molecular formula:
Determine the empirical formula mass:
CrSO4 = 52.00 g/mol + 32.06 g/mol x 2 + 16.00 g/mol x 4 = 156.12 g/mol
Divide the molar mass by the empirical formula mass to obtain the multiplying factor:
392.21 g/mol / 156.12 g/mol = 2.51 (rounded to 3)
Multiply each subscript in the empirical formula by 3 to obtain the molecular formula:
Cr3S3O12
Therefore, the molecular formula of the compound is Cr3S3O12