How many oxygen atoms are in #"120.23 g Fe"_3("PO"_4)_2"#?

1 Answer
Nov 25, 2014

Answer:

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

Explanation:

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 #(8"mol O)/(1 mol Fe"_3("PO"_4)_2")# to determine the number of moles of oxygen. Then multiply the moles of oxygen times #6.022xx"10"^23# #"atoms O"#.

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

#120.23color(red)cancel(color(black)("g Fe"_3("PO"_4)_2))xx(1 "mol Fe"_3("PO"_4)_2)/(357.478color(red)cancel(color(black)("g Fe"_3("PO"_4)_2)))= "0.336328 mol Fe"_3("PO"_4)_2"#

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

#0.336328color(red)cancel(color(black)("mol Fe"_3("PO"_4)_2))xx(8"mol O")/(1color(red)cancel(color(black)("mol Fe"_3("PO"_4)_2)))="2.690624 mol O"#

3. Convert moles O to atoms O.

#2.690624color(red)cancel(color(black)("mol O"))xx(6.022xx10^23"atoms O")/(1color(red)cancel(color(black)("mol O")))=1.6203xx10^24"atoms O"# (answer rounded to five significant figures)