Question

Help! How do I write generic word equation and a chemical equation for the reaction that occurs when an anhydrous salt is placed in water (hydrated)? O.O

Answer 1

mass of empty crucible: 39.43 g
mass of crucible and hydrated salt: 42.43 g
mass of hydrate: 3.00 g
mass of crucible and dehydrated salt (after 1st heating): 41. 49 g
mass of crucible and dehydrated salt (after 2nd-heating): 41.39 g
mass of anhydrous salt: 1.96 g
mass of water released: 1.04 g
% water in hydrated salt:34.67 g

Answer 2

In general if you place a salt in water, it will dissolve to give a solution:
\[Salt + Water \rightarrow Solution\]
Chemically this would be written as
\[Salt _{(s)} \rightarrow Salt_{aq}\]
The subscript s and aq are state symbols - s referring to "solid" and aq referring to "aqueous" (ie, aqueous solution).

Hydrated salts can be written in the form
\[MX.nH_2O\]
Where MX is a salt and n is the number of water molecules present in the hydrated form.

In the dehydration (by heating) that you describe,
\[MX.nH_2O \rightarrow MX + nH_2O\]
Ie, water is liberated.

From the experimental data you have, given the identity of the salt, it should be possible to work out n.

Hope this helps

Answer 3

is it still the same as AB.XH2O -> AB + XH2O?
Also, AB means metal and nonmetal right? Since salt is created from metal and nonmetal?

Why is it that my teacher shows me the same answer you have but of a different question: the reaction when a hydrated salt is heated.

What is the the difference between a hydrated salt that is heated and anhydrous salt placed in water (hydrated)? Please help!

Answer 4

Hi,

When a hydrated salt is heated, the reaction I put last in my answer happens - same as AB - you're exactly right about the composition of a salt :).

When an anhydrous salt is placed in water, it will dissolve - this is what I mentioned at the start of my answer. In theory, though, before dissolution the salt will become hydrated. This would just be the reverse of the dehydration your teacher and I showed (the reaction when a hydrated salt is heated):

\[AB_{(s)} + nH_2O \rightarrow AB.nH_2O \rightarrow AB_{(aq)}\]

Does that help?

Answer 5

So the generic word equation you showed above is for the reaction when a hydrated salt is heated? Not \[AB .XH2O ->AB + XH2O\] (underneath the arrow there's a triangle to identify that it is heated)

And AB.XH2O -> AB + NH2O is for the anhydrous salt is placed in water (hydrated)? What is hydrated?

Answer 6

The two formula in your last comment:

AB.XH2O -> AB + XH2O

refer to the reaction upon heating a sample of hydrated salt.

Hydrated means that the salt, as part of its crystal structure, contains water. An anhydrous salt contains only the ions A+ and B-, while a hydrated salt contains some water molecules too - represented by the ".H2O" in the compound's formula. However, there are so few water molecules that the salt is still a solid!

A sample of anhydrous salt, when added to water, will become hydrated and then dissolve. That's what my formula in my last comment represented.

Since we've discussed quite a few different formulas/reactions here, it might be best if anything else is unsure that we quote the uncertain formulas directly. Through all the comments I think we've worked through the question and the background understanding, so it might help to have another look through if anything is unclear.

Thanks!

Answer 7

thank you so much!! :)

Answer 8

np

Answer 9

hello, I'm sorry to ask another question but how do I \[\eta\] using the information I had?