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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: sundrops on January 21, 2005, 02:14:49 AM

Title: Moles and Molecules
Post by: sundrops on January 21, 2005, 02:14:49 AM

The molecular formula of a substance is C16H17O8.
The molar mass is 337.3g/mol

How many moles of C16H17O8 molecules are in 111mg of this compund?

Title: Re:Moles and Molecules
Post by: sundrops on January 21, 2005, 02:16:05 AM

I would like to know HOW I would find this information - I need help. It's onl like question #2 in my homework and I can't solve it!?!

Title: Re:Moles and Molecules
Post by: Mitch on January 21, 2005, 02:32:57 AM

Start by determining how many moles of the molecule you have.

Title: Re:Moles and Molecules
Post by: sundrops on January 21, 2005, 02:43:00 AM

what do u mean? well there's 337.3 g/mol.
so that would be 337300 mg/mol

I don`t really understand what to do.  ??? I mean how would I figure it out?

Title: Re:Moles and Molecules
Post by: Mitch on January 21, 2005, 02:46:52 AM

How can you multiply or divide those 2 numbers(the 111mg and the 337.3 mg/mol) to end up with a number with units of moles?

Title: Re:Moles and Molecules
Post by: sundrops on January 21, 2005, 02:51:20 AM

so would it be 111g of C16H17O8 * 1mol of C16H17O8 / 337.3g of C16H17O8 = 3.29*10^-4

Title: Re:Moles and Molecules
Post by: sundrops on January 21, 2005, 02:54:20 AM

yay! that was right! thanks!!


except next part is that I need to find the mass of 0.100 mol of this compund.

so would I just go: 0.100 mol C16H17O8 * 337.296g C16H17O8 / 1 mol C16H17O8 = 33.7296g

did I do that right?

Title: Re:Moles and Molecules
Post by: Mitch on January 21, 2005, 02:59:02 AM

looks good, I didn't actually take out a calculator though.

Title: Re:Moles and Molecules
Post by: sundrops on January 21, 2005, 03:03:37 AM

yay! that was good too!

I'm always scared to submit my answers (it's all done online) and you only get 5 tries. So you have to make sure you really understand it and that you have the proper units and proper sig figs - very very annoying! lol

Title: Re:Moles and Molecules
Post by: sundrops on January 21, 2005, 03:12:26 AM

thanks for all your help mitch - i really appreciate it.

but there's one more question.

How many hydrogen atoms are in 1.78 pg of this compound?

here's my reasoning...

(1.78pg) * (1g / 10E^-12pg) * (1mol / 337.296g) * (6.02E23 / 1 mol) = 3.1769E33

how does that look?

Title: Re:Moles and Molecules
Post by: sundrops on January 21, 2005, 03:40:45 AM

I then multiplyed the 3.17797E13 molecules by 17 hydrogen atoms / molecule = 5.40E14 atoms of hydrogen

this turned out to be wrong - can u point out my mistake?