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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: zeoblade on March 01, 2010, 09:26:31 PM

Title: Distinguishing qualitatively HCl and CH3COOH
Post by: zeoblade on March 01, 2010, 09:26:31 PM

I'm trying to think of a qualitative test to distinguish between HCl and CH3COOH and I can come up with nothing other than the reaction rate.

For example:

HCl(aq) + Zn(s) --> ZnCl₂(aq) + H₂(g)
The reaction will happen very fast relative to:

CH₃COOH(aq) + Zn(s) --> Zn(O₂CCH₃)₂(aq) + H₂(g)

Is there a better way to distinguish qualitatively? I'm so tempted to use a pH metre but the purpose is qualitative, not quantitative

Title: Re: Distinguishing qualitatively HCl and CH3COOH
Post by: zeoblade on March 01, 2010, 09:34:49 PM

I was also thinking of using AgNO₃(s) so that with HCl(aq) --> HNO₃(aq) + AgCl₂(s) forms that can be heated to produce Ag(s) and Cl₂(g)

However, AgNO₃(s) + CH₃COOH(aq) --> HNO₃(aq) + AgO₂CCH₃(s) forms that won't give off the yellow-green coloured Cl₂(g)

Is this fair to state?

Also would the acetate decompose to CO₂(g) + H₂O(l)?

Title: Re: Distinguishing qualitatively HCl and CH3COOH
Post by: Borek on March 02, 2010, 03:04:45 AM

Silver idea is not a bad one - what do you know about solubility of siver chloride and silver acetate? What should you observe adding AgNO₃ to both acids?

Note: silver chloride is NOT AgCl₂.

Title: Re: Distinguishing qualitatively HCl and CH3COOH
Post by: 408 on March 02, 2010, 03:20:46 AM

Smell.  ( I am serious)

Title: Re: Distinguishing qualitatively HCl and CH3COOH
Post by: Borek on March 02, 2010, 03:21:49 AM

Deadly serious  ;D

Title: Re: Distinguishing qualitatively HCl and CH3COOH
Post by: zeoblade on March 02, 2010, 04:40:06 AM

Thanks guys,

I have been mainly targeting solubility to get a precipitate on one but not the other since the cation really influences the colour of the solution. But it seems to be a tedious process of blindly choosing complementary ions and checking their solubility. Isn't there some easier way of dichotomously coming to the appropriate ion?

I'm not allowed to use any instrumental techniques such as ion chromatography, just simple qualitative tests involving the use of cations or anions. I instantly thought of odour and pH but I've been restricted to manipulation of ions.

It mainly seems you have to be creative and pluck an ion out of thin air from a VAST knowledge of product solubility, colour, stability. Is there some logical rationale I could use?

Title: Re: Distinguishing qualitatively HCl and CH3COOH
Post by: 408 on March 02, 2010, 12:13:39 PM

Knowing solubility tables far too well.  Use lead nitrate or silver nitrate as said above.  Seeing as you cannot go the easy route of smelling them.