Homework Help: chemistry

Posted by lyne on Monday, January 5, 2009 at 4:29pm.

The element rhenium (Re) has two naturally occurring isotopes, 185Re and 187Re, with an average atomic mass of 186.207 amu. Rhenium is 62.60% 187Re, and the atomic mass of 187Re is 186.956 amu. Calculate the mass of 185Re.

am i supposed to multiply the atomic masses and the percents or something?
im lost..

chemistry - DrBob222, Monday, January 5, 2009 at 4:42pm
yes. Both multiply AND something.
0.6626*X + 0.3740(186.956) = 186.207
Make sure I have these paired right.
X stands for amu Re185. Solve for X.
chemistry - DrBob222, Monday, January 5, 2009 at 4:49pm
You can check your answer this way.
Multiply decimal percent of amu 185 and decimal percent of amu 187, add them together and you should get 186.207.
chemistry - lyne, Monday, January 5, 2009 at 4:59pm
shouldnt it be .626(186.956)+.374*X=186.207
chemistry - DrBob222, Monday, January 5, 2009 at 9:12pm
yes, I don't know why I typed in 6626. It should be 0.626 and 0.374. Neither do I know why I reversed the order when I typed it in BUT I'm glad I put in the post to check my pairings. According to my notes, I have
0.374(X) + 0.626(186.956) = 186.207 which I think agrees with what you have.
My eyesight is not that great as you can tell.
chemistry - Noksie, Sunday, April 17, 2011 at 6:37am
x=186.207-(0.626)(186.956)/0.374=184.953
chemistry - bob, Sunday, October 21, 2012 at 10:11pm
where is the 0.3740 coming from
chemistry - bob, Sunday, October 21, 2012 at 10:11pm
where is the 0.3740 coming from

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