Question

Determine the empirical formula of a compound of a mineral having the percent composition 29.27% O, 24.80% Fe, and 45.93% Cr. Assuming a 100.0 g sample of the mineral, how many grams are made up of oxygen, iron, and chromium, respectively?

____g O

____g Fe

____g Cr

Answer 1

Assuming the sample of mineral to be 100 g , the amount of elements in the sample will be

O = 29.27 % of 100 g = 29.27 grams

Fe = 24.80 % of 100 g = 24.80 grams

Cr = 45.93% of 100 g = 45.93 grams

number of moles of O = 29.27 / 16 = 1.83 moles

number of moles of Fe = 24.80 / 55.845=0.44 moles

number of moles of Cr = 45.93/ 52 = 0.88 moles

Dividing the number of moles by a common factor 0.44 ,

we get the ratio of O : Fe : Cr = 4 : 1 :2

So the empirical formula will be :

O₄FeCr₂ or FeCr₂O₄