How would you calculate the percentage by mass of oxygen in a compound? Chemistry The Mole Concept Percent Composition 1 Answer anor277 Nov 18, 2016 #"%Oxygen"="Mass of oxygen"/"Formula mass of compound"xx100%# Explanation: Let's try this with #"potassium permangante, " KMnO_4#, whose formula mass is #158.03*g*mol^-1#. #"% oxygen "= (4xx15.999*g*mol^-1)/(158.03*g*mol^-1)xx100%~=40%# 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 23080 views around the world You can reuse this answer Creative Commons License