Chemistry 111 Laboratory Alum Synthesis Page C 3 THE SYNTHESIS OF POTASSIUM ALUMINUM SULFATE Alum FROM ALUMINUM SCRAP The Chemical Recycling of Scrap Aluminum This experiment has the following objectives 1 To be aware of the need for recycling solid wastes particularly scrap metal like aluminum 2 To learn some of the chemistry of aluminum 3 To become familiar with the use of laboratory equipment such as beakers flasks Bunsen burners and so on 4 To be able to perform the techniques of weighing gravity and vacuum filtration and crystallization 5 To be able to apply a knowledge of the stoichiometry of a sequence of chemical reactions to the calculation of the percentage yield of alum synthesized from aluminum scrap INTRODUCTION Modern societies have concentrated on what might be considered the most primitive of methods of solid waste disposal burning or burying This type of behavior is a strange anomaly because solid waste is probably the oldest of man s pollutants and yet has only recently received serious attention from scientists and technologists Like all other environmental problems solid waste problems are intensified by modern civilization more people and more things In 1920 the average American generated 2 3 4 pounds of solid waste per day in 1970 the average was 5 pounds per day and by 1980 it was about 8 pounds per day The composition of all this solid waste is shown in the TABLE on the next page it is drawn from a Public Health Service study of municipal refuse for 19661968 Unfortunately the problem is compounded by the fact that one of the most important types of resource at the base of our technological society is metal Metals such as copper chromium molybdenum tin zinc tungsten and aluminum have become as necessary to economics as water and fossil fuels Aluminum is a classic example Aluminum is the third most abundant element and most abundant metal in the Earth s crust It is concentrated in a number of high grade natural bauxite deposits almost all of which are located outside of the U S Changes Revised June 2005 Figure Two views of the unit cell smallest repeating unit of aluminum metal See the model of aluminum on the Chem Lab page for the course Looking at solid waste from the disposal end gives one set of priorities Looking at solid waste from the standpoint of recycling yields a completely different set of priorities and can illustrate areas of technological need that previously have been overlooked The salvage of aluminum from mixed municipal refuse is such an area From Recycling of Used Aluminum Products by Dr Robert F Testin Page C 4 Chemistry 111 Laboratory Alum Synthesis SOLID WASTE PROFILE 1965 to 1968 Item by Weight Paper products 55 0 Glass 7 7 Metals 6 8 Vegetable scraps 2 9 Meat scraps 2 9 Other foods 2 9 Leaves grass etc 10 0 Other 2 8 Adjusted moisture 9 0 in the international situation the so called Third World owns most of the bauxite and the depletion of high grade ores is forcing the aluminum industry to use lower grade ores with correspondingly higher prices for aluminum and products made from it At the same time this is happening the use of aluminum in disposable products e g beverage cans foil etc is increasing enormously Even the most solid of all solid wastes the automobile now contains more aluminum alloys The stimuli to recycle aluminum are thus very strong and are being reinforced by other recent developments The production of aluminum from natural sources like bauxite aluminum oxide Al2O3 and cryolite Na3AlF6 involves an electrolytic process which uses large amounts of electricity The sky rocketing cost of that form of energy is well known The energy costs of recycling aluminum metal by shredding melting and casting are a small fraction about 5 10 of the energy cost of producing the metal from ore Finally in an ironic twist one of the properties of aluminum that is responsible for its current wide spread use can cause a serious environmental problem Aluminum does not corrode as does iron and steel A fresh aluminum surface reacts very rapidly with oxygen to produce an oxide coating that is so Figure An electrochemical cell used to produce aluminum metal The aluminum in the form of compounds such as Al2O3 in Na3AlF6 is electrolyzed reduced at a graphite cathode Because the cell is at a high temperature the aluminum is molten and is drawn off the bottom of the cell See Chemistry Chemical Reactivity 6th edition page 1035 Revised June 2005 Chemistry 111 Laboratory Alum Synthesis Page C 5 tenacious and impervious that no further reaction takes place The thin layer is not necessary Hence skyscraper facings airplanes Airstream trailers and beer cans can be nice shiny objects The discarded aluminum can has become nearly immortal It has an average lifetime in the environment of greater than 100 years There are now a number of successful recycling programs for aluminum cans Collection centers are paying around 15 cents per pound for scrap aluminum The problem of recycling cans that end up in the municipal landfill has not yet been solved but progress is being made in designing large scale separators to separate aluminum steel glass and paper from trash The scrap aluminum is usually shredded melted down cast and eventually made into an aluminum product In this experiment you will be recycling aluminum scrap in a very unusual way and you will produce two products which are potentially very useful hydrogen gas H2 and very pure potassium aluminum sulfate KAl SO4 2 12 H2O or alum Hydrogen gas has great potential use as a fuel if some of its dangerous properties can be controlled mixtures of H2 and air are highly explosive Hydrogen gas when burned properly produces a large amount of heat and no pollution the only combustion product being water Alum is a widely used chemical in industry playing an important role in the production of many products used in the home and industry The pulp and paper industry alone consumes 70 of the more than one million tons of alum produced annually in the U S It is used to size the paper The second largest use is in the purification of water for human and industrial consumption Other uses include soaps greases fire extinguisher compounds textiles leather synthetic rubber drugs cosmetics cement plastics and pickles It is important to note here that this particular process for converting aluminum into alum would produce very expensive alum Alum can be made very cheaply at the moment using clay as the raw material