Thursday
May 5, 2016

# Homework Help: Chemistry

Posted by Kyle on Monday, January 16, 2012 at 11:56am.

If a sample of Co2(CO)8 is found to contain 6*10^-2 mol of C atoms, how many grams of Co atoms are present?

Molar Mass (g/mol)

Co2(CO)8 - 341.95
Co atom - 58.933
C atom - 12.011
O atom - 15.999

Do I need to use the 6*10^-2 mol of C atoms to find how many grams are in this sample of Co2(CO)8? Then from there find how many grams of Co atoms?

By the way, for clarification, what does it mean by "how many grams of X atoms?"

The answer is supposed to be: 0.89872825g

But I'd like an explanation on how to do this problem, thank you.
• Chemistry - Steve, Monday, January 16, 2012 at 12:38pm

Each molecule contains 2 Co atoms and 8 C atoms. So, divide .06moles of C by 4 to get moles of Co

.06/4 = .015 moles of Co

.015mol * 58.933g/mol = 0.883995g

• Chemistry - Kyle, Monday, January 16, 2012 at 12:44pm

Why did you divide .06 moles by 4? Is it because there is a 8:4 ratio of C and Co?

• Chemistry - DrBob222, Monday, January 16, 2012 at 2:01pm

Yes (actually a 2:8 ratio). 0.06 mols C x (2 Co atoms/8 mols C atoms) = 0.06 x (2/8) = 0.015 moles Co
I should point out that there is only 1 significant figure in 0.06 mol C atoms in the problem; therefore, an answer of 0.898728..... is inappropriate. The answer of 0.884 should be rounded to 0.9 g Co or 9E-1.