Preparation of Alum from Aluminum Metal
LABORATORY REPORT 4
PREPARATION OF ALUM
FROM ALUMINUM METAL
Huy Nguyen
October 2nd, 2012
The objective of the laboratory is to synthesize alum (KAl(SO4)2.xH2O) from aluminum powder and to determine the proportion of water in the alum crystals. Alum is a product from the reaction between potassium hydroxide and sulfuric acid. The reaction include several steps, as followed:
Aluminum powder reacts with potassium hydroxide to generate Al(OH)4- ions and release hydrogen.
2 Al(s) + 2 KOH(aq) + 6 H2O 2 K[Al(OH)4](aq) + 3 H2 (g)
A gelatinous precipitate of aluminum hydroxide was created when sulfuric acid was added to the aqueous solution of Al(OH)4- ions.
2 K[Al(OH)4](aq) + H2SO4 (aq) 2 Al(OH)3 (s) + K2SO4 (aq) + 2 H2O
Later, excessive addition of the acid causes the precipitate to dissolve in the solution.
2Al(OH)3 (s) + H2SO4 (aq) Al2(SO4)3 (aq) + 6 H2O
Precipitation of alum was resulted from cooling in ice water bath.
K2SO4 + Al2(SO4)3 + 2x H2O 2 KAl(SO4)2.xH2O
It is noticeable that alum is a hydrate (a hydrate consists of water molecules in its ionic structure), which leads to its solubility in water. However, a minimum amount of cold water will cause the alum to crystallize. The amount of water incorporated in the alum structure should be clearly defined to derive the full formula of alum, which makes it possible for calculations of theoretical, actual and percent yield of alum.
Experimental Methods The experiment was constructed based on the guidelines from Franklin and Marshall Lab Manual1. In a 400 mL-beaker, 0.5 g of aluminum and 2.01g of potassium hydroxide was prepared and mixed together. An amount of 25 mL of distilled water was poured into the beaker in the hood. The mixture was then continuously stirred to help disperse the heat generated from the exothermic reaction. As observed, hydrogen was liberated from the solution, along with aluminum powder gradually darkening and disintegrating into insoluble flakes. It
PREPARATION OF ALUM
FROM ALUMINUM METAL
Huy Nguyen
October 2nd, 2012
The objective of the laboratory is to synthesize alum (KAl(SO4)2.xH2O) from aluminum powder and to determine the proportion of water in the alum crystals. Alum is a product from the reaction between potassium hydroxide and sulfuric acid. The reaction include several steps, as followed:
Aluminum powder reacts with potassium hydroxide to generate Al(OH)4- ions and release hydrogen.
2 Al(s) + 2 KOH(aq) + 6 H2O 2 K[Al(OH)4](aq) + 3 H2 (g)
A gelatinous precipitate of aluminum hydroxide was created when sulfuric acid was added to the aqueous solution of Al(OH)4- ions.
2 K[Al(OH)4](aq) + H2SO4 (aq) 2 Al(OH)3 (s) + K2SO4 (aq) + 2 H2O
Later, excessive addition of the acid causes the precipitate to dissolve in the solution.
2Al(OH)3 (s) + H2SO4 (aq) Al2(SO4)3 (aq) + 6 H2O
Precipitation of alum was resulted from cooling in ice water bath.
K2SO4 + Al2(SO4)3 + 2x H2O 2 KAl(SO4)2.xH2O
It is noticeable that alum is a hydrate (a hydrate consists of water molecules in its ionic structure), which leads to its solubility in water. However, a minimum amount of cold water will cause the alum to crystallize. The amount of water incorporated in the alum structure should be clearly defined to derive the full formula of alum, which makes it possible for calculations of theoretical, actual and percent yield of alum.
Experimental Methods The experiment was constructed based on the guidelines from Franklin and Marshall Lab Manual1. In a 400 mL-beaker, 0.5 g of aluminum and 2.01g of potassium hydroxide was prepared and mixed together. An amount of 25 mL of distilled water was poured into the beaker in the hood. The mixture was then continuously stirred to help disperse the heat generated from the exothermic reaction. As observed, hydrogen was liberated from the solution, along with aluminum powder gradually darkening and disintegrating into insoluble flakes. It
References: 1. Franklin and Marshall College Chemistry 111/112 Laboratory Manual, Fall 2012/Spring 2013, p. 39-41.