What is the percentage by mass of #SO_3#? Chemistry The Mole Concept Percent Composition 1 Answer anor277 Oct 7, 2016 #"% sulfur by mass"# #=# #(32.06*g*mol^-1)/(80.066*g*mol^-1)xx100%# #=# #??# Explanation: #"% sulfur by mass"# #=# #(32.06*g*mol^-1)/(80.066*g*mol^-1)xx100%# #=# #??# #"% oxygen by mass"# #=# #(3xx16.00*g*mol^-1)/(80.066*g*mol^-1)xx100%# #=# #??# The sum of the individual percentages #=100%#; why? Answer link Related questions What is mole percent? Question #e2e8b Question #bc737 Question #bc73b Question #e2e8f Question #b9857 Question #b985b Question #fee41 Question #c5c01 Question #bc73f See all questions in Percent Composition Impact of this question 1312 views around the world You can reuse this answer Creative Commons License