what is the empirical formula for a compound containing 26.57% potassium, 35.36% chromium, and 38.07% oxygen

Question

i have no clue how this is done. plz help

Answer 1

To find the empirical formula, we want to find the moles of each element. If we assume we have 100 g of the unknown, then the percents can be written as grams. Thus,

grams K = 26.57 g

grams Cr = 35.36 g

grams O = 38.07 g

Now converting to moles, we have...

moles K = 26.57 g x 1mol/39.09 g = 0.6797 moles K

moles Cr = 35.36 g x 1 mol/51.99 g = 0.6801 moles Cr

moles O =38.07 x 1 mol/15.99 g = 2.381 moles O

Next, we try to get all whole numbers, so we start by dividing all by the lowest value, i.e. 0.6797

moles K = 0.6797/0.6797 = 1

moles Cr = 0.6801/0.6707 = 1

moles O = 2.38/0.6797 = 3.5

Still don't have whole numbers, but if we now multiply all by 2, we get 2 mol K, 2 mol Cr and 7 mol O.

Empirical formula thus is K₂Cr₂O₇