Question 625307
The masses of the atoms in atomic mass units are 40 for calcium (Ca), 32 for sulfur (S), and 16 for oxygen (O).
The formula weight for a formula unit of {{{CaSO[4]}} (calcium sulfate, anhydrous) is
{{{40+32+4*16=136}}}
The ratio of masses of oxygen to {{{CaSO[4]}}}  is
{{{4*16 oxygen /136 CaSO[4] }}}={{{64oxygen /136CaSO[4]=8oxygen /17CaSO[4]}}}=47%
The ratio applies no matter what unit is used to measure mass, as long as we are using the same unit for both substances.
The amount of oxygen (in grams) in 1224 g {{{CaSO[4]}} is
{{{1224*(8/17)=576}}}
In the mychemistrytutor website the answer may be written as:
(1224 g {{{CaSO[4]}}})(64 g O/136g {{{CaSO[4]}}})= 576 g O
 
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If you are trying to do your chemistry homework, the mychemistrytutor site is more likely to answer, and would answer very quickly.