Purpose: In this experiment, you will be converting the aluminum metal from a beverage

can into the chemical compound potassium aluminum sulfate, KAl(SO4)2•12

H2O, commonly referred to as alum.

Data and Calculations: In this lab, a beverage can is used to get aluminum sheet and then, sheet

is cut into small pieces with scissor. These pieces are further used to get

Alum in last.

Mass weighing bottle + aluminum 12.11 g

Mass of weighing bottle 11.04 g

Mass of aluminum 1.07 g

Concentration and volume of KOH 3 M and 20 mL

Concentration and volume of H2SO4 9 M and 20 mL

Mass weighing bottle and Alum 25.18 g

Mass of weighing bottle 11.04 g

Mass of Alum 14.14 g

Observations:

After rubbing aluminum can becomes shiny like silver color.

After adding KOH to 250 mL beaker containing aluminum chips, it starts bubbling.

After placing on hot plate it starts bubbling vigorously and the KOH solution turns grey

in color.

The aluminum chips were visible for few minutes but with continuous heating it starts

dissolving into solution.

The content turns into black in color due to impurities like paint and plastics.

H2 gas was evolving continuously and silver color aluminum chip turn white.

After taking back beaker from hot plate, the content starts cooling and visible chips were

dissolving and the whole contents turns black.

After the vacuum filtration process the content becomes clear.

Dissolved content containing aluminum is transparent and colorless.

While adding 9 M H2SO4 to the content, the content slowly turns into white color cloud.

After adding whole 20 mL of H2SO4 the content becomes white in color and with

continuous stirring, the white cloud disappears.

The content wasn’t clear so we put it on hot plate and after placing it on hot plate the

content slowly turns clear and transparent.

After 10 minutes the whole solution turns clear.

After 12 minutes, there was formation of crystals (white color). The white color crystals

look like clouds.

After pouring the crystals for filtration, there was no change but specific smell was

coming out.

After rinsing the beaker with ethanol there was no change. The crystals are purely white

and looks like snow and common salt shaped.

The filter flask was partially filled with white color solution.

The while color Alum was ready at end.

Theoretical value of synthesis of Alum:

Chemicals equations involved into the formation of Alum.

2 Al (s) + 2 KOH + 6 H2O 2 K[Al(OH)4] + 3 H2 (l)

2 K[Al(OH) 4] + H2SO4 2 Al(OH)3 (s) + 2 H2O + K2SO4

2 Al(OH)3 + 3 H2SO4 Al2(SO4)3 + 6 H2O

Al2(SO4)3 + K2SO4 + 24 H2O 2 K[Al(SO4)2]•12H2O

2 Al (s) + 2 KOH + 4 H2SO4 + 22 H2O 2 K[Al(SO4)2]•12H2O + 3 H2

Mass of Aluminum used = 1.07 g

Molar Mass of Aluminum = 26.98 g / moles

Number of moles Al = Mass of Al (g)

Molar mass of Al (g/ moles)

Number of moles Al = 1.07 g / 26.98 (g / moles)

= 0.0397 moles

Since, 2 moles of Aluminum gives 2 moles of Alum. So, there is ration of 1:1 .

Numbers of moles of Alum = 0.0397 moles

Molar mass of Alum = 474.39 g / mole

Mass of Alum yielded = Number of moles * Molar mass of Alum

Mass of Alum yield = 0.0397 moles * 474.39 (g / mole)

= 18.83 g

% yield = (Actual yield (g) / Theoretical yield (g)) * 100

= (14.14 g / 18.83 g) *100

= 75.1 %

Discussion: The experimental value for the yielding of alum is 14.14 g and theoretical value is

18.83 g. The percent yield is 75.1 % which is relatively a good result as per waste aluminum can

is concerned. The beverages bottles contain aluminum, plastic and paint of organic compounds

which has much effectively influenced our results. Aluminum beverage cans generally have a

thin coating of plastic on the inside that protects the aluminum from the corrosive action of the

chemicals in the beverage. The outside usually has a thin coating of paint. These coatings must

be removed before any chemical reactions with the metal can be carried out. Aluminum sheet

from aluminum beverages can were cleaned, plastic and paint were removed before the chemical

reactions but there were still spots of plastic and visible paint which can’t be removed easily

from aluminum sheet, as a result it gives absolute error in measurements. For better chemical

reaction, there should be large surface area for chemical absorption process to get chemical

reaction. So, aluminum sheet was cut into tiny pieces but there were still large pieces in the

beaker which may cause error, as chemical reaction do not went properly. While reaction with 20

mL of KOH solution over the hot plate, the whole solution turns black this shows the presence of

impurities into aluminum sheet, as no beverage company use pure aluminum metal for the cans.

The pipe connected to filtrated flask was not tightly held so vacuum pressure might be less and

filtration of content were not obtained properly and we get less liquid for reaction with 20 mL

H2SO4 to get alum. This might be reason we get 14.14 g of actually alum as compared to

theoretically calculated alum (18.83 g). The addition of H2SO4 results in the formation of white

color crystals of alum but to separate it from liquid content it was again filtrated using vacuum

filtration process. The beaker was rinse with ethanol to get all crystals into Buchner funnel but

there was a lot crystals stick with beaker which wasn’t be able to get filtered, moreover by using

excess amount ethanol to get crystals could lead to another chemical reaction and we might have

lost our alum crystals and has got 14.14 g yield as compared to 18.83 g (theoretical).

The primary source of less percent yield (75 %) is because of presence of a lot of impurities in

aluminum sheet. Moreover, the process of vacuum filtration was not that success which lead to

less value of yield (14.14 g) because the crystals were stick to beaker and wasn’t able to remove

for filtration. Also, the aluminum sheet we used, wasn’t pure aluminum metal. It was coated with

plastic and organic paint and aluminum sheet must contain some other metals to make it hard and

stable, so this must has caused error on the result as compared to theoretical value of yield (18.83

g).

Conclusion: To conclude, this experiment was success as we got 75 % of percent yield of Alum

from aluminum beverage can sheet. There were many possible sources of errors in

this lab due to impurities or random errors which may lessen our actual yield, that is;

14.14 g as compared to theoretical value, that is; 18.83 g. This lab was in pair of

two, so we learnt the team work and cooperation.