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Posted by on Wednesday, December 8, 2010 at 6:22pm.

magnesium has 3 isotopes. Magnesium-24 has a percent abundance of 78.99%. Magnesium-26 has a percent of 11.01%. what is the percent abundance of magnesium-25? assume that there are no other magnesium isotopes.

how do i do this please help

  • chemistry - , Wednesday, December 8, 2010 at 7:50pm

    Don't all of the percentages add up to 100%? And you have two of the three?

  • chemistry - , Wednesday, December 8, 2010 at 8:56pm

    thank you

  • chemistry - , Monday, December 9, 2013 at 2:47pm

    There is a fairly simple answer to this:
    The question states that you assume there are three magnesium isotopes. If Magnesium 24 has an abundance of 78.99%, and Magnesium 26 has a percent abundance of 11.01%, the percent abundance of Magnesium 25 is simple to calculate.
    The abundances must add up to 100%, and seeing as we are assuming that there is only one more isotope of Magnesium, we just subtract the sum of the first two abundances from 100%, as shown below:
    100% - (78.99% + 11.01%)
    100% - 90%
    So the abundance of Magnesium 25 would be 10%.

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