Sciencemadness Discussion Board - Bases as solvents, metals

Bases as solvents, metals

Romix - 2-4-2016 at 01:30

I understand what happens when acid reacts with metal.
Halogen gains electrons, releasing hydrogen.

But what happens when base acts as a solvent.
For example Al + NaOH. Hydrogen released here too.
What about ammonia solutions with copper? No hydrogen in this reaction, but it dissolving. Same for nickel but much much slower.

[Edited on 2-4-2016 by Romix]

[Edited on 2-4-2016 by Romix]

ave369 - 2-4-2016 at 02:11

Only metals that are amphoteric in their lowest stable state of oxidation react with alkalis. Hydroxide ion gains electrons, metal gives them resulting in the metal oxide and hydrogen, oxide then reacts with another hydroxide ion giving a metalate (or hydroxometalate) ion.

brubei - 2-4-2016 at 02:15

Pourbaix diagramm gives the state of a metal in different conditions

for exemple: aluminium is corroded in aqueous solution at pH < 4 and pH > 9 while H2O gives H2 or O2

In non acidic condition, corrosion is given by the couple
O_2(g) + 2 H₂O + 4 e^- ⇄ 4 OH^-_(aq) E = +0,40V

As you can see there is no gaz generated.

Then copper is oxidized to oxide or hydroxide (see area pH > 7 Eh/V > 0.4, corresponding to aqueous ammonia)

Then ammonia give complexe with non-valent electron and produce soluble compounds

[Edited on 2-4-2016 by brubei]

By the same way nickel is oxidized in basic aqueous condition, but it tend to produce NiO a solid acting as a protection against oxydation ( Ni(OH)₃ is out of the domain of H2O stability)

[Edited on 2-4-2016 by brubei]

[Edited on 2-4-2016 by brubei]

Romix - 2-4-2016 at 03:25

Quote: Originally posted by brubei

Pourbaix diagramm gives the state of a metal in different conditions

for exemple: aluminium is corroded in aqueous solution at pH < 4 and pH > 9 while H2O gives H2 or O2

In non acidic condition, corrosion is given by the couple
O_2(g) + 2 H₂O + 4 e^- ⇄ 4 OH^-_(aq) E = +0,40V

As you can see there is no gaz generated.

Then copper is oxidized to oxide or hydroxide (see area pH > 7 Eh/V > 0.4, corresponding to aqueous ammonia)

Then ammonia give complexe with non-valent electron and produce soluble compounds

[Edited on 2-4-2016 by brubei]

Copper corrodes, and ammonia dissolves its oxide?
Maybe.

[Edited on 2-4-2016 by Romix]

[Edited on 2-4-2016 by Romix]

Romix - 3-4-2016 at 20:45

Quote: Originally posted by brubei

By the same way nickel is oxidized in basic aqueous condition, but it tend to produce NiO a solid acting as a protection against oxydation ( Ni(OH)₃ is out of the domain of H2O stability)

Yes, right. And it's black.

Romix - 14-4-2016 at 07:45

Oxygen needed in both reactions.