After subtracting the weight of the container, the Vanadium metal inside is

found to weigh 8.34 grams. After reacting with Oxygen the newly formed
compound weighs 21.43 grams. What is the empirical formula?

1 answer

Find moles V.
8.34/molar mass.

Find moles oxygen.
21.43-8.43 = 13.09 g oxygen
moles = 13.09/16 = ??

Now find the ratio in small whole numbers. The easy way to do that is to divide the smaller number of itself (making it 1.000), then divide the other number by the same small number, found to a whole number and that should be the formula.