## What is a formula unit? (Question E9 from Handout #1)

EmilyJoo_1G
Posts: 50
Joined: Thu Jul 25, 2019 12:16 am

### What is a formula unit? (Question E9 from Handout #1)

Question E9 from Handout #1 asks the following:

Epsom salts consist of magnesium sulfate heptahydrate. Write its formula. (b) How many formula units of the compound are present in 5.15 grams?

Im unsure as to what exactly we are supposed to calculate for part b.

jisulee1C
Posts: 149
Joined: Thu Jul 25, 2019 12:17 am

### Re: What is a formula unit? (Question E9 from Handout #1)

A formula unit indicates the lowest whole number ratio of ions in an ionic compound. Compared to a molecule which would be the smallest for a covalently bonded compound.

Michael Nguyen 1E
Posts: 120
Joined: Sat Aug 17, 2019 12:17 am

### Re: What is a formula unit? (Question E9 from Handout #1)

Hi!

A formula unit is the term used to represent one unit of an ionic compound. It is similar to molecules and atoms in that manner. (Atoms are to lone elements as formula units are to ionic compounds.)

As for this problem, you would first convert the 5.15 grams to moles. Then, using Avogadro's number (6.0221 * 10^23) you would convert those moles to formula units of the compound.

Rory Simpson 2F
Posts: 106
Joined: Fri Aug 09, 2019 12:17 am

### Re: What is a formula unit? (Question E9 from Handout #1)

A formula unit is the smallest integer unit possible for ionic compounds. For example, NaCl would be the formula unit for sodium chloride. An ionic compound wouldn't exist alone as a molecule, but the formula unit shows the ratio of ions as part of the larger array of ions. The formula unit for magnesium sulfate heptahydrate would be MgSO4 7H2O.