What are the mole fractions of H3PO4 and water in a solution of 14.5g of H3PO4 in 125g of water?

1 Answer
Feb 6, 2018

For #"H"_3"PO"_4#: #0.0209#
For #"H"_2"O"#: #0.9791#

Explanation:

Well let's start with getting moles of both #"H"_3"PO"_4# and #"H"_2"O"# that are present in this sample.

The molecular weight of #"H"_3"PO"_4# is approximately 97.9 g/mol, and the molecular weight of #"H"_2"O"# is approximately 18.02 g/mol. So:

For #"H"_3"PO"_4#:
#(14.5 "g")/(97.9 "g/mol")=0.1481# moles

For #"H"_2"O"#:
#(125 "g")/(18.02 "g/mol") = 6.937# moles

Now we determine the total amount of moles in the sample:
#n_"total"=0.1481+6.937=7.0848# moles

Now to determine mole fractions, we take the individual component moles and divide by the total moles, or in other words:
#n_"i"/n_"total"#

For #"H"_3"PO"_4#:
#0.1481/7.0848 = 0.0209#

For #"H"_2"O"#:
#6.937/7.0848 = 0.9791#

Note that for water we can take #1-"mole fraction of ""H"_3"PO"_4# and get the same answer.

Hope this helps!