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Need Help on a Few Problems

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August 13, 2006 - 15:44
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coffee
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Need Help on a Few Problems

Just came back to school.. and I realize I've forgotten so many things! ARGG! >_<
So if anyone can, I would really appreciate it you could help and show me how to do these problems asap!

1) An element consists of 1.40% of an isotope with mass 203.973 amu, 24.10% of an isotope with mass 205.9745 amu, 22.10% of an isotope with mass 206.959 amu, and 52.40% of an isotope with mass 207.9766 amu. Calculate the average atomic mass and identify the element.

2) The element rhenium (Re) has two naturally occuring 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.

3) A compound contains only carbon, hydrogen, and oxygen. Combustion of 10.68 mg of the compound yields 16.01 mg CO2 and 4.37 mg H2O. The molar mass of the compound is 176.1 g/mol. What are the empirical and molecular formulas of the compound.

THANKS! :o

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