Synthesis of Alum.docx - Synthesis of Alum Introduction...

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Synthesis of Alum Introduction: Aluminum is the most abundant metal in the Earth’s crust and is mined as the ore called bauxite (Al 2 O 3 ). Despite the abundance, Aluminum requires large amounts of electricity to convert from its ore to the pure metal. In this lab, you will convert the Aluminum metal from a soda can to a product known as Alum whose formula is KAl(SO 4 ) 2 . Background: The production of Aluminum metal from its ore (bauxite) requires several steps. The bauxite (Al 2 O 3 ) must first be dissolved in sodium hydroxide to isolate the Aluminum metal from any other metals. This is due to the fact that Al +3 will form a soluble complex ion with the hydroxide ions as Al(OH) 4 - . Then, the resulting solution can be acidified to recover pure Al 2 O 3 . The Al 2 O 3 is then mixed with cryolite (Na 3 AlF 6 ) and heated to its melting point of between 950 – 980 o C. In the final step, the Al +3 is reduced in an electrolytic cell using up to 350,000 amperes of electricity. Overall, the production of Aluminum metal in just the U.S. uses 5% of our annual supply of electricity. Once Aluminum is refined, the surface of the metal quickly oxidizes to re-form Al 2 O 3 . However, unlike Iron, this oxide coating is impervious and prevents any metal atoms below the surface from oxidizing. This is both a good and bad property. On one hand, metal parts made from Aluminum will remain shiny and look new for a long time (An example of this is any modern commercial airplane). On the other hand, Aluminum discarded to a landfill will not decompose for a very long time. For this reason, it is important that as much Aluminum as possible gets recycled. Also, the cost of recycling is about 5% of the original cost to produce the Aluminum. In this particular lab, you will “recycle” the Aluminum from a soda can into a product called Alum, which is KAl(SO 4 ) 2 . Alum is an important chemical used in both the paper industry and the water purification process.
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