Formula Units

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Gianna Graziano 1A
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Joined: Wed Apr 04, 2018 3:00 am

Formula Units

Postby Gianna Graziano 1A » Tue Apr 10, 2018 8:23 pm

I am confused on what formula units are. I see them coming up in a lot of the problems from outline 1, but have never learned about them in lecture or elsewhere. How do we find formula units? Also, is it always imperative that we convert them to moles?

Jade Corpus-Sapida 1G
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Re: Formula Units

Postby Jade Corpus-Sapida 1G » Tue Apr 10, 2018 11:02 pm

Based off previous posts, formula units appear to be salts and/or the number of "objects"/"things" etc.?
From the online definition: "A formula unit indicates the lowest whole number ratio of ions in an ionic compound."

Units within the formula are atoms of the element present, while coefficients are moles. If the problem gives the amount of atoms, then yes I would assume we would have to convert it (atoms) to moles.

Patience Olsen 1A
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Re: Formula Units

Postby Patience Olsen 1A » Tue Apr 10, 2018 11:09 pm

Formula units are basically empirical formulas for ionic compounds, but in most questions just represent molecules (in their simplest, empirical form). For example, E.9 (b) asks for the number of formula units of magnesium sulfate heptahydrate in a 5.15 g sample of the compound. This question is solved by dividing 5.15 g by the molar mass of the compound. Your answer will then be in moles.
I'm sure it would also be correct to convert your number of moles to the actual number of molecules with Avogadro's number but that just makes it much more complicated than it needs to be.

Jessica Lancisi - 1I
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Joined: Fri Apr 06, 2018 11:03 am

Re: Formula Units

Postby Jessica Lancisi - 1I » Thu Apr 12, 2018 10:50 pm

I read on another post that because formula units apply to salts like NACL, you cannot refer to these salts as molecules? is this true?

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Re: Formula Units

Postby juliaschreib1A » Sun Apr 15, 2018 12:36 pm

To calculate formula units, you use 6.022 x 10^23.

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Re: Formula Units

Postby Chem_Mod » Sun Apr 15, 2018 5:57 pm

formula units mean units of that formula.

For example, suppose one has a small NaCl salt crystal is made up of 9 NaCl compound. Then this crystal has 9 NaCl formula units in it.

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Re: Formula Units

Postby AdityaGuru1H » Mon Oct 01, 2018 10:38 pm

From my best understanding a formula unit refers to a group of atoms that are bonded ionically while a molecule refers to a group of atoms that are bonded covalently, but please feel free to correct me as I am still not 100% sure of this myself

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