The synthesis of alum, KAl(SO4)2⋅12H2O, can be accomplished through the following reactions. Aluminum is first oxidized by potassium hydroxide to form a soluble salt in the chemical reaction.
2 Al(s) + 2 KOH(aq) + 6 H2O(l)2 KAl(OH)4(aq) + 3 H2(g)
After filtration to remove any residual plastic or paint, the solution is clear and colorless. The H2 is evolved as a gas and mixes with the atmosphere (this is why there is no smoking in the lab). The chemical species in solution are K+, Al(OH)4-, and unreacted KOH. Sulfuric acid is added and two sequential reactions occur. Initially, as the acid is added, a precipitate, Al(OH)3 forms.
2 KAl(OH)4(aq) + H2SO4(aq)2 Al(OH)3(s) + 2 H2O(l) + K2SO4(aq) Then as more sulfuric acid is added the precipitate
2 Al(s) + 2 KOH(aq) + 6 H2O(l)2 KAl(OH)4(aq) + 3 H2(g)
After filtration to remove any residual plastic or paint, the solution is clear and colorless. The H2 is evolved as a gas and mixes with the atmosphere (this is why there is no smoking in the lab). The chemical species in solution are K+, Al(OH)4-, and unreacted KOH. Sulfuric acid is added and two sequential reactions occur. Initially, as the acid is added, a precipitate, Al(OH)3 forms.
2 KAl(OH)4(aq) + H2SO4(aq)2 Al(OH)3(s) + 2 H2O(l) + K2SO4(aq) Then as more sulfuric acid is added the precipitate