CHEMISTRY FORM THREE TOPIC 8: EXTRACTIONS OF METALS


 TOPIC 8: EXTRACTIONS OF METALS | CHEMISTRY FORM 3

Occurrence and Location of Metals in Tanzania

Locations of Important Metal Ores in Tanzania

Identify locations of important metal ores in Tanzania

Most metals are found naturally as compounds called minerals. Rocks are made up of crystals of metals. An ore is a rock that contains enough of a metal compounds for it to be worth extracting the metal. The most common ores contain oxides. An example is the ore haematite, which contains iron (III) oxide. Some contain other metal compounds. Malachite contains copper (II) carbonate.

Tanzania is blessed with an assortment of minerals. The mineral found in Tanzania include gold, which is found in Geita (Mwanza), Kahama (Shinyanga), Nyamongo, Buhemba and Majimoto (Mara), and Nzega (Tabora).

Large deposits of iron occur at Liganga in Ludewa (Iringa). Copper is found in Mpanda (Rukwa). We also have sodium which occurs in the form of sodium chloride, at Uvinza (Kigoma), in the form of soda ash (Na2CO3) in lake Natron, as a rock salt in Kilwa and as a dissolved salt (NaCl) in sea water.

The Abundances of Metals in the Earth’s Crust

Compare the abundances of metals in the earth’s crust

Metals occur in the sea and in the earth. The form in which they occur depends on their reactivity. The most reactive metals are extracted from the sea. Calcium is extracted from limestone, chalk and marble in the sea. Metals of medium reactivity are found in the earth in form of oxides and sulphides. Examples of these metals include aluminium, zinc, iron and tin. Least reactive metals such as silver and gold occur as free uncombined elements.

We obtain most of the metals we use from the earth’s crust. The majority of metals are too reactive to exist as natural elements. They are found as compounds in ores. The chief ores in order of their economic importance are oxides, sulphides, chlorides and carbonates.

The most common metal is aluminium, which makes about 7.8% of the earth’s crust, followed by iron, which accounts to approximately 4.5%. Others include calcium (3.5%), sodium (2.5%), potassium (2.5%) and magnesium (2.8%). The remaining metals make about 3% of the earth’s crust.

Chemical Properties of Metals

The Difference between Physical and Chemical Strengths of Metals

Differentiate the physical and chemical strengths of metals

Metals are known to have a greater tendency to lose electrons in the course of which they go into solution as ions. A metal, therefore, may be defined as an element which can ionize by electron loss. The number of electrons lost per atom is the valency of the metal and the ion carries an equal number of positive charges, as: