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### Homework Problem E9 Part B

Posted: **Tue Oct 01, 2019 11:58 pm**

by **Andrew F 2L**

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

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

Posted: **Wed Oct 02, 2019 12:49 am**

by **Doris Cho 1D**

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.

### Re: Homework Problem E9 Part B

Posted: **Wed Oct 02, 2019 10:56 am**

by **ayushibanerjee06**

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

### Re: Homework Problem E9 Part B

Posted: **Wed Oct 02, 2019 11:01 am**

by **Angela Patel 2J**

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).