What is the molecular formula for a #"164.2 g"# sample of a compound that contains #"46.92 g K"#, #"38.52 g S"# and oxygen? The molecular weight of the compound is #"270.4 g/mol"#.
Let's start calculating the weight percentage of the elements in the compound:
by difference oxygen is
Now divide the percentage mass by the atomic mass and obtain the atomic ratio
The ratio among elemnts is
therefore the minimal molecular formula is
with molecular mass of
Molar mass is
The molecular formula for the compound is
- Determine the empirical formula.
- Determine the empirical formula weight.
- Divide the molecular formula weight by the empirical formula weight.
- Multiply the empirical formula weight times the result.
Determine the mass of each element.
Determine the molar mass of each element, which is its atomic weight in g/mol.
Determine the moles of each element by multiplying the given masses by inverse of the molar mass:
Determine the mole ratios for the empirical formula by dividing the number of moles of each element by the smallest number.
The empirical formula is
EMPIRICAL FORMULA WEIGHT
Multiply the subscripts times the molar mass for each element and add the results.
Divide the molecular weight
Multiply the empirical formula