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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: kioplo on April 21, 2005, 07:37:39 PM

Title: Unknown Compound: insoluble in water, it forms a precipitate when added to water
Post by: kioplo on April 21, 2005, 07:37:39 PM

I have an unknown compound that i have to figure out and what i have determined so far is that it is insoluble in water, it forms a precipitate when added to water, it has a melting point over 340 C, and is very soluble in dilute acids.  It would be great if someone could help me narrow down what it could be.  also it is a fine white powder and it smells a lot like naphthalene or moth balls....also when i added it to the nitric acid to test solubility it fizzed for a second while dissolving...

Title: Re:Unknown Compound
Post by: Mitch on April 21, 2005, 10:31:04 PM

That is nearly useless information.

We need a mass spec., proton or carbon NMR, an IR, uv-vis(since you think its an aromatic), in order to figure out what it is.

Title: Re:Unknown Compound
Post by: TCUrob on April 22, 2005, 12:23:44 AM

Quote from: kioplo on April 21, 2005, 07:37:39 PM

I have an unknown compound that i have to figure out and what i have determined so far is that it is insoluble in water, it forms a precipitate when added to water

That's not possible. If your unknown reacts with water, it IS soluble.

Title: Re:Unknown Compound
Post by: Garneck on April 22, 2005, 01:04:37 AM

Yeah, an IR with a 1H NMR should be fine here.  ;D

But probably you don't have that.

Title: Re:Unknown Compound
Post by: xiankai on April 22, 2005, 02:17:47 AM

all i can deduce atm that it is a metal compound (reacts with acid)

and dont think its insoluble because u still see pieces of it. u may have to add excess water.

Title: Re:Unknown Compound
Post by: Borek on April 22, 2005, 04:13:46 AM

Quote

it is insoluble in water, it forms a precipitate when added to water

Please explain, how it can precipitate out of the solution if it was never dissolved? Do you mean it behaves like a sand added to water - falls to the bottom and looks like a precipitate?  :-\

Title: Re:Unknown Compound
Post by: kioplo on April 22, 2005, 07:18:26 PM

well it made the water cloudy and what my chemistry teacher said was a precipitate, however most of what was added was on the bottom of the container....perhaps it is partly soluble in water, but i do not think that the water was over saturated because there was plenty of water...

Title: Re:Unknown Compound: insoluble in water, it forms a precipitate when added to wa
Post by: xiankai on April 25, 2005, 05:07:13 AM

oh yes, u dont add things to acid to test for solubility.

the acid reacts with the compound instead to form different compounds.

and it cant possibly be insoluble, else it will act like an unreactive compound and no reaction takes place at all. what you have mentioned is a result of a reaction.

if u add a white salt and find a white ppt, it could possibly be an insoluble hydroxidem which is the product of the reaction.