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Formula Units

Posted: Mon Oct 01, 2018 5:21 pm
by monikac4k
While working on the textbook problems, I came across problems asking for formula units. I am still confused about what a formula unit is. Can somebody please explain it to me and how to find it?

Re: Formula Units  [ENDORSED]

Posted: Mon Oct 01, 2018 6:52 pm
by Chem_Mod
I will cover this in class.

Molecular formulas refer to molecules.
Formula units refer to salts.

For example NaCl is the formula unit for table salt.
One cannot refer to NaCl as a molecular formula becasue NaCl is not a molecule.

Re: Formula Units

Posted: Wed Oct 03, 2018 1:28 pm
by Riya Shah 4H
So when we say 2NaCl we are referring to 2 formula units of NaCl? Calculating formula units is a little confusing too. Could someone please explain it?

Re: Formula Units

Posted: Wed Oct 03, 2018 2:41 pm
by Kayla Vo 1B
Correct. 2NaCl would mean that there are 2 formula units of NaCl. You usually first calculate the number of moles (divide the mass of the sample by the molar mass) and then multiply it by Avogadro's number (6.022 x 10^23) to calculate the number of formula units. This procedure is the same as if you were asked to find the number of molecules of water in a given mass of water (convert mass to moles and then to molecules) but the units are just a little different.