Homework Help: chemistry

Posted by Luc on Monday, November 7, 2011 at 3:59am.

An element with relative atomic mass 20.8 is found to contain 2 isotopes having a relative atomic mass of 20 and 21.Find the % composition of the element.

chemistry - Dr Russ, Monday, November 7, 2011 at 5:03am
Relative atomic mass = 20.8 g

Let the fraction that is element 20 = x
thus the fraction that is element 21=1-x

so 20x +21(1-x) = 20.8

20x + 21 -21x=20.8

-1x=-0.2

x=0.2 and 1-x=0.8

so 20% element 20 and 80% element 21.
chemistry - mera williams, Monday, November 7, 2011 at 6:32am
20.8%
chemistry - mera williams, Monday, November 7, 2011 at 6:32am
20.8%
chemistry - mera williams, Monday, November 7, 2011 at 6:39am
44%
chemistry - d.r luke, Monday, November 7, 2011 at 7:08am
44%

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