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    A sample of antimony Ar= 121.7 was analyses and was found to consist of 60% 121 Sb and one other isotope. Determine the mass number of the other isotope in the sample of antimony

    I know the answer is Sb123 but idk why so please will someone work through it for me x


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    (Original post by halliethestudent)
    A sample of antimony Ar= 121.7 was analyses and was found to consist of 60% 121 Sb and one other isotope. Determine the mass number of the other isotope in the sample of antimony

    I know the answer is Sb123 but idk why so please will someone work through it for me x


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    Relative atomic mass = [(mass1 x abundance1)+(mass2 x abundance2)]/ total abundance

    So if x is the 2nd isotope's mass...and the abundance is out of 100%, and one of the isotopes is 60%, so the other must be 100-60=40%...

    121.7=[(121 * 60%) + (x * 40%)]/100
    You need to rearrange that to make X the subject.
    Spoiler:
    Show
    X=[121.7*100-(121*60)]/40
 
 
 
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