I am recycling some metals (Aluminum and Zinc).  The salvage yard requires that the metals be kept seperate.  

From my high school chemistry, I remember that Hydrochloric acid (HCL) applied to Zinc (mossy), produces Hydrogen gas (HCL + Zn = H₂ and ZnCl₂).  Supposedly, that is the "test" for Zinc.

However, when I apply Hydrochloric Acid to known Aluminum, it releases a gas also, albeit less of a vigorous reaction.   And again from my high school chemistry, if a gas is produced, it is also most certainly Hydrogen (HCL + Al = H₂ and AlCl₂).

What am I missing here?  How can I determine if the metal(s) in question is/are Zinc or Aluminum using acids (I have both HCL and H₂SO₄ to work with)?

 

33 minutes ago, Bushranger said:

(HCL + Al = H₂ and AlCl₂).

Well, it's 6 HCl + 2Al --> 3 H₂ + " 2 AlCl₃

But that's hardly important.

Both metals (indeed most metals) react with dilute acid to give hydrogen gas.
However, if you take the solution of metal chloride and add an excess of ammonia solution you get different results.

With zinc you get a precipitate of Zn(OH)₂ but that dissolves when you add more ammonia.

With Al you get a white precipitate of Al(OH)₃ which doesn't dissolve when you add more ammonia.

It's worth doing the reactions on known  materials first so you get the "feel" of it.

Having said that, Aluminium is about a third  of the density of zinc, and that's often a pretty good way to tell them apart.

 

Also, it is very common to find alloys that are a mixture of aluminium and zinc.