0.3 Going green with al

Going Green With Al

Objectives

• To prepare common alum, KAl(SO ₄ ) ₂ .12H ₂ O, from a discarded aluminum beverage can.
• To perform qualitative analysis on alum.
• To investigate the acid-base behavior of aluminum compounds.

Grading

Your grade will be determined based on the following:

• Quiz (10%)
• Lab Report Form (90%)

Before coming to lab...

         Read the lab instructions

         Print out the lab instructions and report form, take the online quiz

Introduction

Aluminum is the most abundant metal in the earth's surface (7.5% by mass). Rubies and sapphires contain aluminum and it is used in a range of products from rocket fuel to antiperspirants. All of these products contain aluminum metal or aluminum compounds of various kinds. The abundance of aluminum, coupled with its attractive combination of physical and chemical properties, accounts for the fact that it is one of the principal industrial raw materials used by industrialized societies. Production of aluminum from raw materials is an energy intensive process.

Since the metal is not consumed rapidly by corrosion, the amount of scrap aluminum grows rapidly while the available supply of raw materials for the manufacture of aluminum decreases. The average predicted longevity of an aluminum can along the roadside is 100 years.

Environmental problems thus created are typical of those of several different metals. One obvious solution to the problem is to recycle the used fabricated aluminum into other useful metallic objects or into aluminum compounds. Aluminum metal can be recovered from scrap by melting the metal and separating it from solids and volatile impurities. This process uses a large amount of energy.  The energy requirement to prepare an aluminum can from recycling is only 5% of the energy required to produce the can from bauxite ore.

This experiment illustrates a chemical recovery process in which waste aluminum is converted chemically into an aluminum compound, hydrated potassium aluminum sulfate, KAl(SO ₄ ) ₂ 12 H ₂ O, or common alum. Although alum is an important industrial compound, the method of preparation in this experiment is not the way alum is obtained for use in industry. Nevertheless, this experiment will illustrate an interesting example of the reduction of environmental waste. "Alum" is a generic term that describes hydrated double salts of certain metals having the generalized formula, [MM' (SO ₄ ) ₂ .12 H ₂ O], in which M (univalent) is commonly Na ⁺ , K ⁺ , NH ₄ ⁺ , or Rb ⁺ and M' (trivalent) is commonly Al ³⁺ , Ga ³⁺ , V ³⁺ , Cr ³⁺ , Mn ³⁺ , Fe ³⁺ , or Co ³⁺ . True alums crystallize in well-defined octahedral shapes and many are beautifully colored, particularly those containing d -block transition metals. The ancient Egyptians, Greeks and Romans used alum as a mordant in dyeing cloth, which we will meet again in our last lab for this semester. A mordant contains metal ions that bind dyes to the fabric. Presently alum is used to harden photographic film, to prepare pickles, as a mordant, and for other purposes.