The mass of water is 18.00 grams per mole. What is the % of oxygen in water? Chemistry The Mole Concept Percent Composition 1 Answer anor277 May 26, 2018 #"%O"_"by mass"=89%# Explanation: We want the #"mass of oxygen"/"mass of water"xx100%#...and for a molar quantity of water this is... #(16.00*g*mol^-1)/(18.00*g*mol^-1)xx100%=88.9%#.. 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 1914 views around the world You can reuse this answer Creative Commons License