writing the formula of a molecule

[Jackie Ngo 1C]

hi! I'm stuck on question E9 of the Review of Chemical & Physical Principles. it lists that I need to write magnesium sulfate heptahydrate as a formula. how would I do that/read it? thanks so much for your time!

[Henri_de_Guzman_3L]

A magnesium ion is Mg2+
Sulfate is SO4 2-
Together that makes MgSO4

The heptahydrate basically just adds H2O at the end. Hepta- is a prefix for 7.

So the official formula is MgSO4 . 7H2O
In chemistry, it's standard to add a little dot between the compound and the hydrate

[maldonadojs]

I began this problem writing Magnesium Sulfate as MgSo4. Then the prefix hepta- refers to the number 7. Hydrate also refers to just water so it would result in MgSo4 7H2O.

[Jovian Cheung 1K]

Magnesium is Mg. It forms the ion Mg²⁺.
Sulfate refers to the sulfate ion, which is a polyatomic ion with formula SO₄^2-.
As their charges have the same absolute value, which is 2, their ratio in an ionic compound is 1:1.
Thus Magnesium Sulfate is MgSO₄. (As you see, the 2+ and 2- cancel each other out.)

As for heptahydrate, hepta- refers to seven, and -hydrate refers to water/H₂O.
Thus the heptahydrate means 7H₂O.

Combining the two, magnesium heptahydrate is MgSO₄ • 7H₂O
I'm guessing that sections about ionic bonding and polyatomic ions (Dr Lavelle said we'd eventually memorize the frequently seen ones) would be related to this problem. Can also check out hydrated ionic compounds / hydrates, as this is an example of one. Hope this helps! :0)

[Ruiting Jia 4D]

A magnesium ion is Mg2+
Sulfate is SO4 2-
Together that makes MgSO4

The heptahydrate basically just adds H2O at the end. Hepta- is a prefix for 7.

So the official formula is MgSO4 . 7H2O
In chemistry, it's standard to add a little dot between the compound and the hydrate

For quizzes/tests, would we have to automatically know how to add hydrates to compounds? I understand where the + 7H2O comes from, but I was wondering if we had to memorize prefixes for numbers such as hepta- in order to compose a chemical equation or formula.

[Henri_de_Guzman_3L]

While Dr. Lavelle didn't explicitly state to do so, I think it would generally be a good idea in chem to know these anyway. They're not hard! I pasted them below, they're pretty intuitive:

1: mono-
2: di-
3: tri-
4: tetra-
5: penta-
6: hexa-
7: hepta-
8: octa-
9: nona-
10: deca-