Question

If 7.50 g of the unknown compound contained 0.250 mol of C and 0.500 mol of H, how many moles of oxygen, O, were in the sample?

Answer 1

Answer:  0.25 moles O in the sample

Explanation:

0.250 moles:   C = (0.250 moles)*(12 g/mole) = 3 grams C

0.500 moles H:  H = (0.500 moles)*(1 g/mole) = 0.5 grams H

Total mass is 7.5g

Subtract C and H to find grams O  (7.5 g -(3 grams C + 0.5 grams H) = 4.0 grams O.  Molar mass of O is 16 grams/mole.

Moles O = 0.25 O in the sample

The empirical formula is C1H2O1,  possibly formalhyde.