Question

Percent Yield: The final step is to determine the yield of the praction, both in terms of the mass of the final produet obtained and as the percent yield, which indicates the effectiveness of the reaction Mass of wateh glass+alum_SL 3824 Mass of watch ples_43.3413 Mass of alum covered 12.9 113 Siner the formula mass of aluminum and alum are often very different, you cannot compare the mass of product obtained against the mass of starting material used in the reaction to determine the theoretical and percent yield of a praction. To do this, you need to know how many moles of aluminum go into each mole of alum (Hint: Look at the overall reaction!) and the formula weight of alum. Summarize your results in the spaces below, and show all calculations in the spaces where indicated. Moles aluminum : moles alum Formula weight of alum p/mol Theoretical yield alum Percent yield alum Calculation of Formula Weight of Alum. KAl(SO), - 12 H,0 Calculation of Theoretical Yield Percent Yield Calculation ds Scanned with CamScanner

Answer 1

1) Given,
Mass of alum = 12.8713g
Atomic mass of aluminium = 26.9815 g
Molecular mass of alum = 474.4 g/mol

Moles of alum = Mass/ Molar mass
=12.8713/474.4
=0.027 moles

One mole of aluminum atoms has a mass of 26.98 grams, and contains 6.02×10²³ atoms.
Dividing 26.98/ 6.02×10²³ yields a mass of 4.48×10⁻²³g for one aluminum atom.

There is one aluminium atom in alum,so mass is 4.48×10⁻²³g.

Mass of aluminium = 4.48×10⁻²³g

Moles of aluminium = Mass/ Molar mass
= 4.48×10⁻²³/26.9815
= 1.66 x 10^-24

Moles of aluminium : Moles of alum = 1.66 x 10^-24 : 0.027

2) Formula of alum is KAl(SO4)2.12H2O
Mass of 1 K atom = 39.09 g
Mass of 1 Al = 26.98g
Mass of 2S = 32.06 x 2 = 64.12g
Mass of 20 O = 20 x 16 = 320g
Mass of 24 H = 24g

Formula mass of alum = 39.09 + 26.98 + 64.12 + 320 + 24 = 474.19 g

3) Calculate Theoretical yield of alum: = Mass of Al x  (1mol Al/26.99 g Al) x (1 mol Alum/ 1 mol Al) x (474 g Alum / 1 mol Alum)

= 4.48×10⁻²³ x (1mol Al/26.99 g Al) x (1 mol Alum/ 1 mol Al) x (474 g Alum / 1 mol Alum)

= 7.9 x 10^-22g Alum

4) Calculate %Yield:
= (Mass of Alum/theoretical yield) x 100%

= (12.8713/7.9 x 10^-22) x 100%

= 1.62 x 10^-22 x 100%

= 1.62 x 10^-20

Alternate way

1) Given,
Mass of alum = 12.8713g
Atomic mass of aluminium = 26.9815 g
Molecular mass of alum = 474.4 g/mol

Moles of alum = Mass/ Molar mass
=12.8713/474.4
=0.027 moles

Mass of aluminium = X g

Moles of aluminium = Mass/ Molar mass
= X/26.9815

Moles of aluminium : Moles of alum = X/26.9815 : 0.027

2) Formula of alum is KAl(SO4)2.12H2O
Mass of 1 K atom = 39.09 g
Mass of 1 Al = 26.98g
Mass of 2S = 32.06 x 2 = 64.12g
Mass of 20 O = 20 x 16 = 320g
Mass of 24 H = 24g

Formula mass of alum = 39.09 + 26.98 + 64.12 + 320 + 24 = 474.19 g

3) Calculate Theoretical yield of alum: = Mass of Al x  (1mol Al/26.99 g Al) x (1 mol Alum/ 1 mol Al) x (474 g Alum / 1 mol Alum)

= X x (1mol Al/26.99 g Al) x (1 mol Alum/ 1 mol Al) x (474 g Alum / 1 mol Alum)

= X x 17.6 g Alum

4) Calculate %Yield:
= (Mass of Alum/theoretical yield) x 100%

= (12.8713/ X x 17.6) x 100%

= (0.73/X) x 100 %

= 73/X %