What is oleum?
We can consider oleum as a solution of #"SO"_3# in #"H"_2"SO"_4#.
Addition of water to oleum converts the free #"SO"_3# into #"H"_2"SO"_4#, and the resulting solution will contain only #"H"_2"SO"_4#.
#"SO"_3 + "H"_2"O" → "H"_2"SO"_4#
What is 109 % oleum?
109 % oleum means that we must add 9 g of water to 100 g of the oleum to convert all the #"SO"_3# to #"H"_2"SO"_4#.
How much #"SO"_3# is in 109 % oleum?
#M_text(r): 80.06color(white)(m)18.02color(white)(mml) 98.08#
#color(white)(mmll)"SO"_3 + "H"_2"O" → "H"_2"SO"_4#
#"Mass of SO"_3 = 9 color(red)(cancel(color(black)("g H"_2"O"))) × ("80.06 g SO"_3)/(18.02 color(red)(cancel(color(black)("g H"_2"O")))) = "40 g SO"_3#
So, 100 g of 109 % oleum contains 40 g #"SO"_3# and 60 g #"H"_2"SO"_4#.
Calculate the mass percent of oxygen in 109 % oleum
In #"SO"_3#,
#"Mass of O" = 40 color(red)(cancel(color(black)("g SO"_3))) × "48.00 g O"/(80.06 color(red)(cancel(color(black)("g SO"_3)))) = "24 g O"#
In #"H"_2"SO"_4#,
#"Mass of O" = 60 color(red)(cancel(color(black)("g H"_2"SO"_4))) × "64.00 g O"/(98.08 color(red)(cancel(color(black)("g H"_2"SO"_4)))) = "39 g O"#
#"Total mass of O = 24 g+ 39 g = 63 g O"#
#"% O" = (63 color(red)(cancel(color(black)("g"))))/(100 color(red)(cancel(color(black)("g")))) × 100 % = 63 %#
