What is the percent by mass of oxygen in #Mg(NO_3)_2#? Chemistry Matter Atomic Mass 1 Answer anor277 Jan 30, 2017 #%O~=65%# Explanation: #"Percentage oxygen"# #=# #"Mass of oxygen"/"Molar mass of compound"xx100%# #(6xx15.999*g*mol^-1)/(148.32*g*mol^-1)xx100%=??# Answer link Related questions How do you calculate the atomic mass of carbon? How are atomic mass and mass number different? How do you calculate atomic mass from isotopic composition ? How do atomic mass and atomic weight differ? How do atomic masses reflect isotope abundances? How do atomic masses vary throughout the periodic table? How much atomic mass is in hydrogen? What atomic mass does ekasilicon have? Why are atomic masses of most of the elements fractional? What is atomic mass? See all questions in Atomic Mass Impact of this question 2832 views around the world You can reuse this answer Creative Commons License