# Tough Chemistry Question

1. Feb 1, 2005

### Raza

Hello, I got this really hard question on my chemistry assignment and I don't know where to start; I am completely lost.

If 125g of magnesium sulfate heptahydrate is completely dehydrated, how many grams of anhydrous magnesium sulfate will remain?

Any help would be greatly appreciated!

2. Feb 1, 2005

### hypermorphism

Do you know the formula for the above mixture ? What does the formula tell you about how much each part contributes to the mass ?

3. Feb 1, 2005

### Raza

is it Mg2SO3 . 7H2O?

I could probably solve this if I knew what anhydrous meant.

4. Feb 1, 2005

### dextercioby

That's not SULPHATE,that's a wrong version of SULPHYTE.You need another formula...

Anhydruous=without water...

Daniel.

5. Feb 1, 2005

### Raza

I am sorry, I do not get this; could you please rephrase it for me?What's sulfyte?
and what is a difference between dehyration and anhydrate?

Last edited: Feb 1, 2005
6. Feb 1, 2005

### dextercioby

$MgSO_{3}$ is MAGNESIUM SULPHYTE and $MgSO_{4}$ is MAGNESIUM SULPHATE.One of them comes from the sulphurous acid,the other from sulphuric acid...

DEHYDRATION=losing water.
ANHYDROUS=without water...

Daniel.

7. Feb 1, 2005

### Raza

I finally get the question but how do I solve it?
I done this before but with knowing the weight of each elements.

Last edited: Feb 1, 2005
8. Feb 1, 2005

### dextercioby

Well,1 mole of $MgSO_{4}\cdot 7 H_{2}O$ has a certain mass...Can u compute it...?How about the mass of 1 mole of $MgSO_{4}$ ??

Daniel.

9. Feb 2, 2005

### GCT

You can observe the formula and from this find the final mole value of magnesium sulfate heptahydrate; find the molar mass of the compound and then find the realistic mole value using the 125 grams.

You know that for every one mole of the compound, there is 7 moles of H20. This should give you a stoichiometric ratio 7 moles of H20/1 mole of the compound. Convert using this ratio to moles of water. From this mole value, convert to grams of water. Subtract this value from 125, and that should be your answer.

10. Feb 2, 2005

### saltydog

I'd like to help:

mol. wgt of MgS04*7H20 = 246.3
mol.wgt of MgS04 = 120.3

Thus, the ratio of anhydrous/hydrous (without water/with water) = 0.488

Thus, when you remove the water from 125 grams of the hydrate, the remaining is:

125*0.488=61 grams MgSO4 left.

I believe that's right. It's been a while and I don't want to make it worst for you.

Salty

Last edited: Feb 2, 2005
11. Feb 2, 2005

### Raza

Thank you all, I got how you solve it now.
It seems so easy after you get what is doing on