How many atoms (total) are in one formula unit of Ca
3(PO
4)
2? (I know that the answer is 13 b/c of the answer key, but I am having trouble doing the actual work and I come no where close to 13.)
My attempt:
The total grams of the above is 310.18 grams. I found the % of each of the elements by dividing the total grams of each element by the total grams (310.18) x 100 and got the following: (Ca - 39%), (P - 20%) and (0 - 41%).
I then found the amount of moles of each element by dividing its percent by its atomic mass and I got the following: (Ca - .9730538922), (P - .6457862448) and (O - 2.5625).
I then divided the amount of moles that I got for each element by the smallest one (the moles of phosphorus) to get the empirical formula and came up with Ca
2PO
4.
For my conversion from grams to atoms I calculated the number of grams in the empirical formula and came up with 175.13 g. I converted this to atoms by dividing this number by 310.18g (the original number of grams in the original molecular formula given) and multiplied it by 6.02x10
23 and I am getting 3.4x10
23.
I have looked it over a few times and re-done the calculations and not sure if I am missing a step, doing a step completely wrong ...