A compound is found to be 38.76% calcium, 19.97% phosphorous and 41.28% oxygen. What is the empirical formula for this compound?

The empirical formula is Ca₃P₂O₈.

Assume that you have 100 g of the compound.

Then you have 38.76 g Ca, 19.97 g P, and 41.28 g O.

Now, we must convert these masses to moles and find their ratios.

If the number in the ratio are not close to integers, you multiply them by a number that makes them close to integers.

From here on, I like to summarize the calculations in a table.

Element Mass/g Moles Ratio * 2 Integers

Ca 38.76 0.967 07 1.4998 2.9995 3

P 19.97 0.644 82 1 2 2

O 41.28 2.580 0 4.0011 8.0023 8

The empirical formula is Ca₃P₂O₈.