Calculate the number of oxygen atoms in 120.23 g of iron (II) phosphate, Fe3(PO4)2?

There are eight moles of oxygen atoms in each mole of ##"Fe"_3("PO"_4)_2"##. To answer this question, you must convert the given mass of ##"Fe"_3("PO"_4)_2"## to moles of ##"Fe"_3("PO"_4)_2"##. Then multiply the moles of ##"Fe"_3("PO"_4)_2"## times eight mol O/1 mol ##"Fe"_3("PO"_4)_2"## to determine the number of moles of oxygen. Then multiply the moles of oxygen times ##"6.022 x 10"^23## atoms O.

Given/Known: mass of ##"Fe"_3("PO"_4)_2"## = ##"120.23g"## molar mass of ##"Fe"_3("PO"_4)_2"## = ##"357.478g/mol"## 1 mole ##"Fe"_3("PO"_4)_2"## contains 8 moles oxygen atoms 1 mole O atoms = ##"6.022 x 10"^23## ##"atoms"##

Unknown: number of oxygen atoms in ##"120.23g Fe"_3("PO"_4)_2##

Solution:

1. Convert given mass of ##"Fe"_3("PO"_4)_2"## to moles.

##"120.23g Fe"_3("PO"_4)_2"## x ##"1 mol"/"357.478g"## = ##"0.336328mol Fe"_3("PO"_4)_2"##

2. Convert moles ##"Fe"_3("PO"_4)_2"## to moles O.

##"0.336328mol"## ##"Fe"_3("PO"_4)_2"## x ##"8 mol O""/1mol Fe"_3("PO"_4)_2""## = ##"2.690624 mol O"##

3. Convert moles O to atoms O.

##"2.690624 mol O"## x ##"6.022 x 10"^23## ##"atoms O""/1 mol O"## = ##"1.6203 x 10"^24"####"atoms O"## (answer rounded to five due to 120.23)

Answer:

##"120.23g"## ##"Fe"_3("PO"_4)_2## contains ##"1.6203 x 10"^24"## ##"atoms O"##.