What happens when aluminium powder is boiled with concentrated aquous solution of sodium hydroxide?
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There are actually two reactions involved in reacting aluminum metal in sodium hydroxide. You see, aluminum is a VERY reactive metal. It forms a thin oxide coating (Al2O3) almost instantly on exposure to air and that coating prevents further reaction with the metal, thus making the world safe for soda and beer cans (not to mention beer kegs!).
So if you want to react aluminum with sodium hydroxide, the first reaction you will need is one to get rid of that pesky aluminum oxide coating!
This is how:
Al2O3 + 2 NaOH --> 2Na+ + 2[Al(OH)4]-
The species, [Al(OH)4]- is the tetrahydroxoaluminate complex ion. It only appears at high pH. At low pH you cannot get it to form and thus, you will get no further reaction because you cannot dissolve the aluminum oxide coating on the metal. Fortunately, we are using sodium hydroxide and low pH is not even a remote possibility!
Now that you have pure aluminum metal, you can react that with more sodium hydroxide:
2 Al + 2 NaOH + 6 H2O → 2 Na+ + 2[Al(OH)4]- + 3 H2 (gas)
So if you want to react aluminum with sodium hydroxide, the first reaction you will need is one to get rid of that pesky aluminum oxide coating!
This is how:
Al2O3 + 2 NaOH --> 2Na+ + 2[Al(OH)4]-
The species, [Al(OH)4]- is the tetrahydroxoaluminate complex ion. It only appears at high pH. At low pH you cannot get it to form and thus, you will get no further reaction because you cannot dissolve the aluminum oxide coating on the metal. Fortunately, we are using sodium hydroxide and low pH is not even a remote possibility!
Now that you have pure aluminum metal, you can react that with more sodium hydroxide:
2 Al + 2 NaOH + 6 H2O → 2 Na+ + 2[Al(OH)4]- + 3 H2 (gas)
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