Question

Synthesis of Alum (Potassium Aluminum Sulfate) from Aluminum Aluminum cans can be recycled to make potassium aluminum sulfate dodecahydrate, KAK(SO)12H20, which is abbreviated to "alum". The 12 waters are part of the overall formula. Alum can be used to make dyes, printing fabrics, making paper, adhesives, pickling of food and vets use it to induce a dog to throw up. x 1 rxn 2 run 3 The following are the four reactions that lead to alum: Al(s) + 2 KOH + 6H 0 - 2 K[Al(OH)] + 3 H2 2 K[Al(OH)] + H SO. 2Al(OH),(s) + 2 H2O + K SO 2 Al(OH), + 3 H SO. - Al(SO4) + 6H20 Al:(SO4)3 +K SO4 + 24 H0 2 KAI(SO)212H 0 rxn 4 The overall reaction is: 2 Al(s) + 2 KOH(aq) + 4H2SO4 (aq) + 22 H2O → 2 KAI(SO.)•12H20 (5) + 3 H2 (8) Aluminum metal is dissolved in KOH to form the complex ion Al(OH), and H(g). This is exothermic and the hydrogen gas should not be inhaled and is highly flammable. Sulfuric acid is then added slowly and Al(OH), will form initially as a lumpy mass, and this will dissolve when heated. If left to stand overnight some triangular crystals of alum will form. The percent yield of the reaction can be calculated as follows: % yield = experimental yield -x100 theoretical yield Exp 8 Page 1 of 6 Rev 1/20

Answer 1

2. Mol of aluminium = weight/molecular weight

0.577/27 = .02137

Now convert moles of Al to moles of alum using the stoichiometric factor from the balanced chemical equation.

Mol of Alum = .02137

Mass of alum = mol of alum x molecular weight of alum

.02137 x 474.39 = 10.13 gram (theotrical Yield)

Net Mass of Alum = 53.624 - 45.282 = 8.34 gm (practical Yield)

% Yield = (Practical/Theotrical) x100

(8.34/10.13) x100 = 82

Post lab question:

1. Triangular shape

2. If % yield is more then 100%, it means that Crystal is not completely dry and there will be presence of moisture.

3. 2Al(s) + 3CuSO4(aq) ———→ Al2(SO4)3(aq) + 3Cu(s)

Limiting reagent: CUSo4 is excess reactant and Al is limiting reactant

3 moles of Cu produces from 2 moles of Al

mol of Al = .321/27 = .0118 mol

mol of Cu = 3/2 x.0118 = .0178 mol

theotrical yield of Copper = .0178 x 63.5 = 1.132 gm

4. actual yield = 1.06 gm

% yield = Actual /theotrical x100

1.06/1.132 x100 = 93.63