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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: aidanggg on May 14, 2019, 09:54:34 PM

Title: Need help with qualitative analysis lab.
Post by: aidanggg on May 14, 2019, 09:54:34 PM
Doing a qualitative analysis, and having trouble finding the cation/anion. If anyone can help me find out what the hell the compound is, I'd appreciate it greatly. I have guessed three times, with both the cation and anion being incorrect. I guessed NH4NO2, Ca(NO3)2, and Mg3PO4. Both parts of each of these three are incorrect. Below are a list of the characteristics, as well as the cations and anions it could be.

The compound is a colorless crystalline substance, that is very soluble in water.

When using blue litmus paper, the paper in a solution of water and the unknown turns the paper VERY slightly reddish.

When doing the flame test, the flame is a slightly lighter color orange than the flame when using no sample.

The ignition test turns the unknown into a liquid, and when cooled, the substance crystallizes and creates a 'film' that is cracked.

When put in dilute 6M sulfuric acid, the unknown turns slightly yellow. When this mixture is heated, the unknown produced a reddish-brown liquid, and an awful smell.

When put in concentrated 18M sulfuric acid, the same effect is shown when burned, but much more volatile. A greenish-white gas is produced, and emits a disgusting odor, an augmented odor seen in the 6M.

When a few drops of 6M NaOH is dropped into a solution of the unknown and water, a precipitate is NOT formed. and there is no noticable effect.

The possible cations are Li, Na, K, Sr, Ba, Fe, Ni, Cr, Co, Cu, Al, Zn, and Pb

The possible anions are a carbonate (CO3, HCO3 doesn't matter, C2H3O2, SO3, SO4, Cl, Br, and I.

 I can only guess incorrectly a limited amount of times, and this is my class final. Any help is appreciated, thanks in advance.
Title: Re: Need help with qualitative analysis lab.
Post by: mjc123 on May 15, 2019, 04:29:17 AM
Did you view the flame test through a violet glass?
Do you know of anything that is a reddish-brown liquid and whose name means "stench"?
Title: Re: Need help with qualitative analysis lab.
Post by: AWK on May 15, 2019, 03:57:27 PM
Color of salt (and possibly solution after dissolving salt) - 4 cations excluded
Test with 6M sulfuric acid - the next 3 cations excluded
flame test indecisive - but the next 2 cations excluded.

Of the remaining 3 cations, only one produces an acidic solution of the salt, but this indicates an incorrect NaOH test result (too concentrated solution). This cation gives a precipitate with ammonia, and the other 2 cations do not give.
The 6M sulfuric acid test also excludes almost half of the anions. The remaining anions may be differentiated by solutions of BaCl2 and AgNO3 (+ color of precipitate +  light)