## Formula Units [ENDORSED]

monikac4k
Posts: 56
Joined: Fri Sep 28, 2018 12:25 am

### Formula Units

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?

Chem_Mod
Posts: 18022
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 418 times

### Re: Formula Units  [ENDORSED]

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.

Riya Shah 4H
Posts: 65
Joined: Wed May 02, 2018 3:00 am

### Re: Formula Units

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?

Kayla Vo 1B
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

### Re: Formula Units

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.