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Properties of Aluminum and Its Compounds

Objectives

  • To prepare common alum, KAl ( SO 4 ) 2 . 12 H 2 O size 12{ ital "KAl" \( ital "SO" rSub { size 8{4} } \) rSub { size 8{2} } "." "12"H rSub { size 8{2} } O} {} , from a discarded aluminum beverage can.
  • To perform qualitative analysis on alum.
  • To investigate the acid-base behavior of aluminum compounds.

Grading

You grade will be determined based on the following:

        Pre-lab (10%)

        Lab Report Form (80%)

        TA evaluation of lab procedure (10%)

Before coming to lab…..

        Read the lab instructions

        Print out the lab instructions and report form

  • Complete the pre-lab, due at the beginning of the lab. See page 616 in Brown, LeMay and Bursten for the definition of amphoteric behavior.

Introduction

Aluminum is the most abundant metal in the earth's surface (7.5% by mass). 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 size 12{ ital "KAl" \( ital "SO" rSub { size 8{4} } \) rSub { size 8{2} } "." "12"H rSub { size 8{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 ] size 12{ \[ ital "MM"' \( ital "SO" rSub { size 8{4} } \) rSub { size 8{2} } "." "12"H rSub { size 8{2} } O \] } {} , in which M (univalent) is commonly Na + size 12{ ital "Na" rSup { size 8{+{}} } } {} , K + size 12{K rSup { size 8{+{}} } } {} , NH 4 + size 12{ ital "NH" rSub { size 8{4} rSup { size 8{+{}} } } } {} , or Rb + size 12{ ital "Rb" rSup { size 8{+{}} } } {} and M' (trivalent) is commonly Al 3 + size 12{ ital "Al" rSup { size 8{3+{}} } } {} , Ga 3 + size 12{ ital "Ga" rSup { size 8{3+{}} } } {} , V 3 + size 12{V rSup { size 8{3+{}} } } {} , Cr 3 + size 12{ ital "Cr" rSup { size 8{3+{}} } } {} , Mn 3 + size 12{ ital "Mn" rSup { size 8{3+{}} } } {} , Fe 3 + size 12{ ital "Fe" rSup { size 8{3+{}} } } {} , or Co 3 + size 12{ ital "Co" rSup { size 8{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. 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.

Experimental procedure

Wear safety goggles. Wear gloves when using concentrated acid and base.

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Source:  OpenStax, General chemistry lab spring. OpenStax CNX. Apr 03, 2009 Download for free at http://cnx.org/content/col10506/1.56
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