## Homework Problem E9 Part B [ENDORSED]

Andrew F 2L
Posts: 103
Joined: Sat Aug 17, 2019 12:17 am

### Homework Problem E9 Part B

I am a little confused as to what a formula unit is because the online definition says it is the empirical formula. After looking through and finding the answer, I am also still confused as to why we divide 5.15 by Epsom's molar mass.
Thank you

Doris Cho 1D
Posts: 53
Joined: Thu Jul 11, 2019 12:16 am

### Re: Homework Problem E9 Part B  [ENDORSED]

the formula unit is basically the empirical formula, so it's the lowest whole number ratio of ions in an ionic compound.
we divide 5.15 by the total mass of Epsom salts because of the formula of finding the number of moles, n=m/M, then, in this case, you multiply by Avogadro's number.

ayushibanerjee06
Posts: 177
Joined: Thu Jul 11, 2019 12:16 am
Been upvoted: 1 time

### Re: Homework Problem E9 Part B

It's poorly worded but you basically just multiply by Avogadro's number to find out how much you have of MgSO4*7H20

Angela Patel 2J
Posts: 110
Joined: Sat Aug 24, 2019 12:17 am

### Re: Homework Problem E9 Part B

You are basically trying to find the number of salt molecules in 5.15 g. To do this, you have to convert grams to moles by dividing by the molar mass of the whole molecule. Then you must convert that number of moles to number of molecules by multiplying by 6.022 x 10^23 (the number of molecules in one mole).