Laboratory Exercise: Smelting of Lead

Transcription

1 CHEM 109 Introduction to Chemistry Revision 1.0 Laboratory Exercise: Smelting of Lead In this laboratory exercise we will carry out a pyrometallurgical conversion of Lead Oxide into elemental Lead. This is the second step in the smelting of the ores of Lead to produce the free metal. Cerussite = Lead Carbonate Lead Oxide Elemental Lead As we have discussed, the elements Arsenic, Antimony, Bismuth and Zinc were all discovered by the metallurgist before 1600 AD because the naturally occurring ores of these substances can be relatively easily smelted. For example, the Zinc containing ore Calamine can be mixed with organic matter, such as Wool or Cow Dung, and heated to form Zinc. During the heating, a two step process occurs. Initially the mineral is converted to the Oxide of Zinc: Calamine Zinc Oxide + Gaseous Byproducts This Oxide then reacts with Carbon Monoxide, that forms as a result of the incomplete burning of the organic matter, to form Zinc metal. Zinc Oxide + Carbon Monoxide Zinc + Carbon Dioxide Something similar can be done to produce Lead. Minerals such as Cerussite that contains Lead Carbonate can be calcinated to form an Oxide of Lead. Cerussite Lead Oxide + Gaseous Byproducts Subsequent heating in an organic material, we will use a piece of filter paper as our organic matter, results in the formation of the element. Lead Oxide + Carbon Monoxide Lead + Carbond Dioxide

2 In this case, the Lead will form in a molten state that will naturally separate from other materials present in the ore. Rapid cooling of the molten Lead will allow it to form the metal before it can be re-oxidized to Lead Oxide.

3 Procedure Perform the following experiment in the Fume Hood. Compounds of Lead and its vapor are quite Toxic. 1. Obtain a small porcelain crucible and a 5cm filter paper. Moisten the paper and use it to line the lower portion of the crucible tightly. (This will prevent the forming Lead from reacting with the porcelain and cracking the crucilbe.) The paper should cover the lower third of the crucible. 2. Obtain two pieces of 7.5cm filter paper. Quarter each piece into a cone. Insert one cone into the other to form a double cone. Moisten the double cone and carefully insert it into the crucible. Make sure the double cone fits tightly into the crucible. 3. Scoop out a generous portion of Lead (II) Oxide, such that it will fill approximately one third of the double cone and place it in the filter paper. Caution: Lead (II) Oxide is toxic. Wear gloves and work in a fume hood. Make sure it is not spilled. Also, do not breathe the dust. 4. Fold over the top edges of the cone such that the Lead (II) Oxide powder is fully contained in the cone. 5. Cover the crucible and support it by a clay triangle on a ring attached to a ring stand. 6. In a well-ventilated fume hood, gently heat the crucible with a cool flame from a Meker burner. (This is to drive off the Water.) Do not heat it so hard as to burn the filter paper. 7. Then strongly heat the crucible to a Red Heat for approximately 40 minutes.

4 8. Before removing the crucible from the heat, gently agitate it. Do this by using your tong to clasp the clay triangle and rock it back and forth. (This causes the droplets of molten Lead to fall to the bottom of the crucible.) 9. Turn off the burner and remove the cover of the crucible. Rapidly pour the material's in the crucible into a 400 ml beaker half-full of Water. (This cools the molten Lead such that it will form the metallic solid.) 10. Recover the Lead and dry it. Obtain a 3 dram vial and submit a sample of your product. Label the vial with the following information: Name(s) Name of Element Symbol of Element Date

5 Smelting of Lead Observations: Name: Date: Signature:

6 Post Lab Questions: 1. Proceed to the Mineral Museum and make observations of the following Ores. (Include the Source and Museum Number for the Ore as well.) Cerussite (Carbonate of Lead) Smithonsite (Carbonate of Zinc) Malachite (Carbonate of Copper) Cinnabar (Sulfide of Mercury)