Find the molecular formula of an acid with a molar mass of 98 grams per moles and the percentage composition of the elements in the acid is as such: hydrogen=2%, sulphur=33%, oxygen=65% ?

1 Answer
Feb 22, 2018

Answer:

#"H"_2"SO"_4#

Explanation:

We must first find the empirical formula.

We can say that, in a #100"g"# sample, we have #2"g"# hydrogen, #"33g"# sulfur, and #65"g"# oxygen.

Converting to moles:

#2"g H"*(1 "mol H")/(1 "g H")= 2 "mol H"#

#33"g S"*(1 "mol S")/(32 "g S")=1.03"mol S" #

#65 "g O"*(1 "mol O")/(16"g O")=4.06"mol O"#

We must divide each mole number by the smallest number, which, here, is #1.03#. Then round to the nearest whole number.

For hydrogen: #2/1.03=1.94~~2#
For sulfur: #1.03/1.03=1#
For oxygen: #4.06/1.03=3.94~~4#

Putting them all together, we get:

#"H"_2"SO"_4#, sulfuric acid.

We must check if the molar mass of sulfuric acid is #98"g"#:

#(1*2)+32+(16*4)=98#

So the molecular formula is also #"H"_2"SO"_4#, sulfuric acid.