Acid + Metal reactions...

[MDJH]

One thing about acids that caught my attention back in high school chemistry was that they reacted chemically with metals to form hydrogen gas. Since then, I haven't done much of this in high school or college chemistry labs, but I've looked at youtube chemistry videos too, and found some things about acids and metals slightly confusing.

 

For example, according to

, aluminum is resistant to nitric acid; yet copper isn't. Hydrochloric acid, on the other hand, supposedly doesn't react with copper but does react with aluminum.

 

Another thing is how strong bases react with metals too, such as how sodium hydroxide supposedly reacts with aluminum to form hydrogen; so hydrochloric acid and sodium hydroxide placed in separate aluminum containers would react with the containers, but mixing them beforehand would give sodium chloride, which supposedly wouldn't react with the containers?

 

Is there any chart saying which acids and bases react with which metals? Or any way otherwise of finding out whether or not a given acid or base would react with a given metal?

[UC]

The problem here is that you are comparing two entirely different reactions.

 

When you use HCl, you are basically doing chemistry with the H+ ion present. The Cl- is pretty much inert. Look up an activity series. HCl will attack anything above hydrogen, including, but not limited to, lead, tin, zinc, aluminum, magnesium, sodium, etc. Lead is a bit fussy since lead chloride is insoluble and will form a protective coat that stops the reaction from proceeding, but it will react on the surface and heating helps drive it further. Copper is below hydrogen and so is not attacked.

 

When you use dilute nitric acid, the reactions are identical, but when you use concentrated nitric acid, you are no longer doing chemistry with that H+. Instead, you are utilizing the nitrate portion, which is a powerful oxidizing agent when in high concentration. The nitrate portion is reduced to NO2 gas and the metal in question is oxidized. This reaction allows concentrated nitric acid to also attack metals that are "below" hydrogen on the activity series (to a point). Mercury, copper, and silver are all readily attacked by this reaction.

 

The only reason that aluminum escapes oxidation is a total fluke. Aluminum has a high propensity to form a protective layer of aluminum oxide (corundum, the stuff rubies and sapphires are made of) and both in everyday air and under the strongly oxidizing conditions of concentrated nitric acid, this is exactly what happens. In more dilute solutions, the acidity would be able to dissolve this layer as aluminum nitrate and then the acid could attack as usual.

 

Magnesium is fairly close in reactivity to aluminum, but doesn't form such an oxide layer. It is rapidly attacked by strong nitric acid, as aluminum would be if it weren't for the pesky oxide layer. Of course, the oxide layer is what makes aluminum so great as a building material. Without it, anything made of aluminum would crumble in a few months at most from oxidation by air.

[MDJH]

When you use HCl, you are basically doing chemistry with the H+ ion present. The Cl- is pretty much inert. Look up an activity series. HCl will attack anything above hydrogen, including, but not limited to, lead, tin, zinc, aluminum, magnesium, sodium, etc.

According to Wikipedia, iron is above hydrogen on the activity series. Would hydrochloric acid attack steel, or would the carbon hold the reaction back?

 

When you use dilute nitric acid, the reactions are identical, but when you use concentrated nitric acid, you are no longer doing chemistry with that H+. Instead, you are utilizing the nitrate portion, which is a powerful oxidizing agent when in high concentration.

Ah, so nitric's corrosiveness has more to do with its anion than its hydronium... would the same apply to other nitrate salts, or does the hydronium still have to be present for such reactions to work?

 

The nitrate portion is reduced to NO2 gas and the metal in question is oxidized.

"Oxidized" as in given an oxide compound, or "oxidized" as in loses electrons? And where does the third oxygen atom in the nitrate ion go?

 

Of course, the oxide layer is what makes aluminum so great as a building material. Without it, anything made of aluminum would crumble in a few months at most from oxidation by air.

So would this mean that a can made of "aluminum" is actually aluminum oxide on the outer surface?

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And another thing, what about bases? I've heard that aqeuous sodium hydroxide reacts with aluminum to form hydrogen gas, how do reactions between metals and strong bases work?