# Homework Help: 5 moles of Hydrogen Iodide dihydrate,

1. Jun 4, 2009

### DarylMBCP

If I have 5 moles of Hydrogen Iodide dihydrate, for example, what is the mass? I knw that I have to tke the number of moles times the molar mass to find the mass but what is the molar mass of the compound I suggested? Do I hve to include the extra 2H2O part when finding the molar mass? Thanks for the help.

2. Jun 4, 2009

### alxm

Re: Hydrates

Yup. The water's going to be there if you weight it, right?

3. Jun 4, 2009

### GCT

Re: Hydrates

Yes , an example of another hydrate is the hydrate of hydrogen phosphate , it's crystalline which is able to be isolated.

4. Jun 4, 2009

### DarylMBCP

Re: Hydrates

Ok, thanks guys. Btw, how do I find the number of moles of Hydrogen Iodide dihydrate in 1dm3 of aqueous solution if the concentration of Hydrogen Iodide dihydrate is 1mol/dm3? Is is even possible to have the concentration of a hydrate in water? Thanks for the help again.

5. Jun 5, 2009

### Staff: Mentor

Re: Hydrates

If I dissolve 1 mole of substance in 1 liter of solution I have 1M solution. Doesn't matter if it was hydrate, dihydrate or something else. But as solution prepared by dissolving 1 mole of dhydrate is no different from the solution prepared by dissolving 1 mole of anhydrous salt (or 1 mole of decahydrate) - this 'hydrate' part is omitted.

There are probably very specific cases when such solutions will differ - for example it can be impossible to prepare concentrated solution of some substance using hydrated salt (too much water to get correct concentration). But these are rare cases, that can be safely ignored at first approach.

6. Jun 5, 2009

Re: Hydrates

Borek do you know who came up with the idea to shorten the word mole to mol?I think it was a brilliant idea and a great time saver.

7. Jun 8, 2009

### DarylMBCP

Re: Hydrates

K, thnks for the help guys.