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In a periodic table, the average atomic mass of magnesium is given as 24,312 u. The average value is based on their relative natural abundance on earth. The three isotopes and their masses are " "_(12)^(24)Mg (23.98504 u), " "_(12)^(25)Mg (24.98584 u) and " "_(12)^(26)Mg (25.98259 u). The natural abundance of " "_(12)^(24)Mg is 78.99% by mass. Calculate the abundances of the other two isotopes. |
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Answer» SOLUTION :It is given that abundance of `" "_(12)^(24)Mg` (23.98504 u) is 78.99%. Let abundance of `" "_(12)^(26)Mg` (25.98259 u) be X%. Then abundance of `" "_(12)^(25)Mg` (24.98584 u) will be `[100 - (78.99 + x)]% or (21.01 - x)%`. `therefore` Average atomic mass `24.312=(23.98504 xx 78.99 + 24.98584 (21.01 - x) + 25.98259 (x))/100 implies 2431.2 = 1894.5783 + 524.9525 + 1.0006 x implies x= (2431.2 - 1894.58 -524.95)/1.0006=11.7 %`. Hence, the abundance of `" "_(12)^(26)Mg` is 11.70% and that of `" "_(12)^(25)Mg` is (21.01 - 11.70) =9.3%. |
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