# Chemistry

posted by Kate

I have realized I don't understand Avagado's number at all

My book shows me this diagram instead of just providing a simple formulas that makes no sense at all

here is what I have made sense of so far

(6.022 x 10^23 atoms/mol)(mass of element) = molecular mass

were molecular mass is just the mass number off the periodic table with units g/mol

solving for mass of element will provide the units of g/atoms which makes perfect sense so I think I have this part down if you want to be gramtically correct g/atom

Here's a sample problem in which I would use this equation: Calculate the mass in grams of a single carbon-12 atom

(12.0 g/mol)/(6.022 x 10^23 atoms/mol) = 1.993 x 10^-23 g/atom

Also
(molecular mass)n = mass of element

were mass is the mass of the element given in g and molecular mass is the mass number from periodic table with units g/mol

n is the number of moles

solving for n provides moles for the final unit so I think I get this equation down

Example probelm: How many moles of He atoms are in 6.46 g?

(6.46 g)/(4.003 g/mol) = 1.61 mol

I'm trying to solv this problem

How mnay molecules of ethane C2H6 are present in .334 g of C2H6?

Now I don't now how to solve the problem I posted above were its asking me for molecules

Can someone just show me the apropriate formulas as I'm just reading this crazy diagram and trying to make sense of it and deriving the formulas from it myself... thanks

1. DrBob222

OK.
You are correct that
moles = grams/molar mass
AND
atomic mass in grams/6.022 x 10^23 = mass of one atom.

# molecules in 0.334 g ethane.
Convert to moles.
moles = grams/molar mass.
0.334/30 = ?? I estimated the 30; you need to confirm it and change if appropriate.
We know 1 mole of anything contains 6.022 x 10^23 molecules; therefore,
# molecules = 6.022 x 10^23 molecules/mole x ??moles from above = # molecules.
By the way, I notice throughout the post that you are omitting an h in WHERE which made it a little difficult to understand when I first read it as WERE.

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