How would you prove that sodium hydroxide is a base without using a litmus paper to test? Give the equation for the reaction?
It is through the equation that is Al2O3 + 2NaOH ->2Na +2[Al(OH)4]-
You can do a reaction with sodium hydroxide which will proceed only if the pH is very high, proving sodium hydroxide is a high pH base.
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 there you have it. Caution, the reaction liberates a lot of heat, and hydrogen gas, and it usually ignites.