# Is it Economical to Recycle Aluminum? No quiz today to provide time for proposals and calculations.

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Is it Economical to Recycle Aluminum? No quiz today to provide time for proposals and calculations

Multi-Step Synthesis It all starts with aluminum… Target compound: KAl(SO 4 ) 2  12 H 2 O …from, say, an old aluminum can. Alum Potassium aluminum sulfate dodecahydrate

Multi-Step Synthesis Conversion of Al into a soluble salt 2 Al(s) + 2 KOH(aq) + 6 H 2 O  2 K + + 2 Al(OH) 4 - + 3 H 2 (g) A coordinate ion: Al(OH) 4 - KAl(SO 4 ) 2  12 H 2 O tetrahydroxoaluminate

Multi-Step Synthesis Conversion of Al(OH) 4 - into an insoluble salt 2 Al(OH) 4 - + H 2 SO 4 (aq)  Don’t forget there is potassium ion hanging around. KAl(SO 4 ) 2  12 H 2 O 2 Al(OH) 3 (s) + SO 4 2- + 2 H 2 O(l) Need to decompose this.

Multi-Step Synthesis Final assembly of KAl(SO 4 ) 2  12 H 2 O 2 Al(OH) 3 (s) + 3 H 2 SO 4 (aq)  Remember? There is potassium ion hanging around. KAl(SO 4 ) 2  12 H 2 O 2 Al 3+ + 3 SO 4 2- + 6 H 2 O(l) Al 3+ + K + + SO 4 2- + 12 H 2 O(l)  KAl(SO 4 ) 2  12 H 2 O Ta daaaa

Calculations For equation 1 –Calculate the amount of 2 M KOH needed for a 1.0 g sample of Al. You will actually use 2x this amount You will need to recalculate all amounts for your actual sample 2 Al(s) + 2 KOH(aq) + 6 H 2 O  2 K + + 2 Al(OH) 4 - + 3 H 2 (g)

Calculations For equation 2 –Calculate the amount of 9 M H 2 SO 4 needed Calculation must take into account: –Amount of Al(OH) 4 - produced in equation (1) –Amount of excess KOH that must be neutralized »What is the KOH to H 2 SO 4 ratio? –Increase the amount of H 2 SO 4 calculated by 2x You will need to recalculate all amounts for your actual sample 2 Al(OH) 4 - + H 2 SO 4 (aq)  2 Al(OH) 3 (s) + SO 4 2- + 2 H 2 O(l) 2 Al(s) + 2 KOH(aq) + 6 H 2 O  2 K + + 2 Al(OH) 4 - + 3 H 2 (g)

Calculations For equation 3 –Calculate the amount of 9 M H 2 SO 4 needed. You will need to recalculate all amounts for your actual sample Increase this volume by 2x and add it to the volume from reaction (2) Steps 2 and 3 can be combined into one step by adding the entire volume of H 2 SO 4 at one time 2 Al(OH) 3 (s) + 3 H 2 SO 4 (aq)  2 Al 3+ + 3 SO 4 2- + 6 H 2 O(l) 2 Al(OH) 4 - + H 2 SO 4 (aq)  2 Al(OH) 3 (s) + SO 4 2- + 2 H 2 O(l) 2 Al(s) + 2 KOH(aq) + 6 H 2 O  2 K + + 2 Al(OH) 4 - + 3 H 2 (g)

Types of filtration Gravity –Used to remove impurities –Use a small piece of glass or cotton wool in place of filter paper Vacuum (Büchner) –Used to isolate product

Other lab notes Never heat any reaction to boiling Remember that cans have paint and an inner coating Cut aluminum to ~1 cm 2 pieces to react Cover beaker when heating reaction (1). Allow reaction (1) to cool before adding H 2 SO 4.

Other lab notes If the solution has impurities after reaction (1) then gravity filter. If the solution is not clear after reaction (3) add additional H 2 SO 4 in squirts until all white gelatinous material dissolves. Don’t waste time here. Water and ethanol for wash should be ice cold. Crystals should be dried in a 70°C oven for ~30 minutes. Weigh the vacuum filter paper before filtering. Label with a pencil.

Proposal List of procedures at each step The type and volume of reagent added at each step Name and signature of each group member on proposal When you think you’re finished, you may leave

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