Zinc isn't the ONLY thing that bubbles with acid

[el34]

Like many others I've used muriatic acid (hydrochloric acid) to test for zinc. You hear "if the acid makes it bubble, you got zinc!".

But zinc isn't the only metal that reacts. Actually lead does too, but not much. From http://au.answers.yahoo.com/question/index?qid=20100311034531AAxxxwG -


For a metal to react with an acid to form a salt and hydrogen gas, it has to be above hydrogen in the electrochemical series (ECS).

The Electrochemical Series is a list of elements in order of their reactivity (high to low).
The list is as follows: Potassium(most reactive), Sodium, Calcium, Magnesium, Aluminium, Zinc, Carbon, Iron, Tin, Hydrogen, Lead, Copper, Silver, gold(least reactive)In your experiment, the Magnesium reacted most vigorously hence producing a lot of Hydrogen gas, which when lit with a glowing splint burned with a pop.

Mg + 2HCl ------------------->MgCl2 + H2

Zinc should also have produced hydrogen gas quickly, however not as quickly or vigorously as Magnesium. Maybe a smaller amount of zinc was used in the experiment - hence the proportion of Hydrogen gas produced would be less.

Zn + 2HCl --------------------> ZnCl2 + H2

Aluminium should also produce hydrogen gas when reacted with HCl acid, however the aluminium may have been coated in Aluminium Oxide (due to corrosion with oxygen in the air).
This coating has to be dissolved by the Hydrochloric Acid before the main reaction proceeds.
So the reaction takes longer to start but when it does it will produce Hydrogen gas.

To dissolve the Al2O3 (aluminium oxide coating the aluminium metal)
Al2O3 + 6HCl---------------------------> 2AlCl3 + 3H2O
The main reaction then is:
2Al + 6HCl -----------------------> 2AlCl3 + 3H2

Finally Copper will not react with Hydrochloric Acid to produce Hydrogen gas as it is below Hydrogen in the Electrochemical Series.

[evan price]

Right... But when dealing with metals that we would be casting with (IE- they look and feel like lead) dripping acid on the suspect metal will give a nice violent fizz if there is zinc, whereas lead gives a scant few bubbles.

I don't know where you are going to find potassium or sodium in free air that is not reacting spontaneously. I don't think anybody will be mistaking magnesium, calcium, aluminum or copper for lead. And I doubt we'll find appreciable gold or silver in our scrap lead.

I mean, it's nice that you posted the scientific reactions for us.

[btroj]

True. Another great example of scientifically factual information that just doesn't matter to us.

If it looks like lead but reacts vigorously with acid then it is most likely zinc.

It isn't the reaction that matter but rather the rate and nature of the reaction.

[mold maker]

The best use of acid reaction is to determine pewter from the mostly zinc look alikes. The pewter only changes color while the zinc substitutes fizz and bubble.

[el34]

My first and only zinc party came from a $100 batch of range lead bought from a scrap dealer. At least I think it was zinc based on "if you ever get the oatmeal you'll know it" comment I received months ago. The disbelief led me to the pool store for a jug of muriatic, which 'proved' the zinc content. Later, after flux-skim-flux-skim-flux-skim, I took an ingot for analysis and it measured 0.66% zinc. I couldn't imagine how that could happen with range lead then realized many of the jackets were brass, like Montana Gold bullets, and perhaps the zinc came from them.

"If it bubbles you got zinc" might not be the whole story and I wanted to know what else would react with muriatic. Sure, the other metals in the list are improbable within the scope of boolit alloy, I'm grasping at anything to explain my experience. I thought the list of acid-vulnerable metals and the degree of bubbling might be useful, but I should have stripped out the equations, sorry about that. Being simple, I thought no bubbles=lead, any bubbles, gentle or violent,=zinc. It's good to know the whole story.

[bangerjim]

Hydrochloric acid HCl ( muriatic to the pool people) will only clean lead. It will definitely attach zinc and is about the only test the "average Joe" has to see if he has lead and not zinc. Pure tin is another story. It is shinier and is much lighter than lead and you do not really need to acid test for it.

And I have seen laments on here where some have bought items made of aluminum thinking they hit the pewter mother load, only to find out it is pretty much worthless aluminum. Al reacts with HCl also......not tin/pewter.

Zinc is the enemy we are after here. Shady loves it!

bangerjim

[kevin c]

My own experiences (sorry for the thread resurrection) was the slow formation of tiny bubbles on the surface of marked pewter, the same but less with pure tin from Rotometals, and the same but a bit more with a piece that was roughly 4% Sb, 2% Sn and the rest Pb. The bubbles took 30 seconds or more to form. No fizzing at all. The pure didn't change at all, but the other specimens were stained by the acid (no surface prep done).

ETA: and I think Shady is not trading for zinc any more?

[triggerhappy243]

muriatic acid will immediately react with zinc. Like BAM, THERE IT IS. I do not know if aluminum will "FLOAT OUT" of molten lead or not, but I would like to believe it does.

el34, that zinc could have come from cast bullets that were contaminated from newer w/w, or even the zinc plating that is on w/w clips. Hard to say where it came from.