CHAPTER 4 | Reactivity of Metals
4.1 | Variety of Minerals
A variety of minerals are found in the crust that are commonly found in rocks.
What are minerals?
Minerals - natural substances with a fixed chemical composition.
Minerals exist in the form of: -
Elements (Gold, Silver, Mercury, Platinum, Carbon and Sulfur)
Compounds (Bauxite, Hematite, , Galena, Cassiterite, Pyrite, Magnesite & Calcite)
Gold
Silver
Carbon
Sulphur
Galena
Bauxite
Pyrite
Magnesite
Physical & Chemical Characteristics of Minerals
Physical Properties - Hardness and mineral colour
Colour
Hematite - Reddish-black
Malachite - Green
Calcite / Limestone - White
Galena - Gray
Cassiterite - Black
Hardness
Sclerometer (a tool to measure mineral hardness)
The Mohs Scale determines mineral hardness
Calcite (scale 3), Diamond (Scale 10- hardest)
How to use Sclerometer
Chemical properties - Solubility in water, mineral heating effect, reaction with acids & alkali.
Soluble in water
Minerals containing sodium & potassium only dissolve in water
The effect of heating
Minerals that contain metal oxides are usually not dissolved when heated. However, if heated with carbon, pure metal and carbon dioxide gas will be produced.
Minerals containing carbonate and sulfide metals are dissolved when heated.
Example:
Calcium carbonate -> Calcium oxide + carbon dioxide
Zinc sulphide -> Zinc oxide + sulphur dioxide
Metals reacts with acid
Minerals containing metal oxides and carbonates dissolve in acid and release carbon dioxide gas.
Calcium carbonate + hydrochloric acid --> calcium chloride + carbon dioxide + water
Uses of Minerals
Calcium oxide and calcium carbonate - neutralize acidic soils.
Calcium carbonate - used in gas furnaces to remove impurities during iron extraction.
Silicone dioxide - make glass.
Aluminum oxide - a substance in sunscreen, lipstick & nail polish.
4.2 Reactivity Series of Metals
Reactivity Series of Metals Based on Reactions with Oxygen
Metal heated with oxygen will produce metal oxide.
Different metals have different levels of reaction with oxygen.
Example:
Iron + oxygen --> Iron oxide
Magnesium + oxygen --> Magnesium oxide
Copper + oxygen --> Copper oxide
In a vigorous reaction between a more reactive metal such as magnesium and oxygen, a bright flame is observed.
In a less vigorous reaction between a less reactive metal such as iron and oxygen, only a glow or slow change in colour is observed.
Reaction of magnesium with oxygen
Reaction of iron with oxygen
Reactivity Series of Metals Based on Reactions with other metals
The position of a metal in the reactivity series of metals depends on the reactivity of the metal when reacting with oxygen.
More reactive metals will remove oxygen from less reactive metal oxide when both metals react.
Zinc is more reactive than copper. When the mixture of zinc and copper oxide is heated, zinc will remove oxygen from the copper oxide, while zinc will become zinc oxide
Zinc + Copper oxide --> Zinc oxide + Copper
Magnesium is more reactive than zinc. When the mixture of zinc and magnesium oxide is heated, there no reaction occur.
Zinc + Magnesium oxide --> no reaction occur
Position of Carbon & Hydrogen in the Reactivity Series of Metals
Metals which are less reactive than carbon in the reactivity series of metals can be extracted from their ores through the reduction of the oxide of these metals by carbon.
Examples
Zinc oxide + Carbon --> Zinc + Carbon dioxide
Lead (II) oxide + Carbon --> Lead + Carbon dioxide
The metal that more reactive than carbon in it metal reactivity series cannot be extracted from their ores.
Example
Aluminium oxide + Carbon --> no change
Application of the position of carbon in the reactivity series of metals for industrial use is metal extraction.
Reduction of Copper oxide with hydrogen
Extraction of Metals
Metals which are less reactive than hydrogen in the reactivity series of metals can be extracted from their ores through the reduction of the oxide of these metals by hydrogen.
Examples
Iron (III) oxide + Hydrogen --> Iron + water
Lead (II) oxide + Hydrogen --> Lead + water
The metal that more reactive than hydrogen in it metal reactivity series cannot be extracted from their ores.
Example
Aluminium oxide + Hydrogen --> no change
Hydrogen cannot reduces aluminium oxide
4.3 Extraction of Metals from their Ores
Extraction of metals is the process to obtain metals from their ores.
For metals higher than carbon in the reactivity series of metals, the extraction of the metal from its metallic compound is through electrolysis.
Potassium, sodium, calcium, magnesium and aluminium
For metals lower than carbon in the reactivity series of metals, the extraction of the metal from its ore is through the reduction of its oxide with carbon.
Zinc, iron, tin and lead
Extraction of the copper and mercury metals is done through direct heating of the metallic compounds.
Process of Iron Extraction
The extraction of iron from its ore is carried out in a blast furnace.
A mixture of concentrated iron ore or iron oxide, coke and limestone is added into a blast furnace through the top
A very hot blast of air is pumped into the furnace through the bottom.
Reactions that occur in the furnace at high temperature.
Production of iron
Iron(III) oxide + carbon -->iron + carbon dioxide
Iron(III) oxide + carbon monoxide--> iron + carbon dioxide
Iron(II) oxide + carbon--> iron + carbon dioxide
Production of slag
Calcium carbonate -->calcium oxide + carbon dioxide
Calcium oxide + silicon dioxide -->calcium silicate
At high temperature in the furnace,
iron that is produced will melt. The molten iron that has solidified is known as cast iron.
slag that is produced will melt. From time to time, the molten slag is tapped off and used to make the base of buildings and roads.
Mining issues in Malaysia
Air pollution due to burning of fuels
Water pollution due to cleaning of ore
Soil erosion due to mining of ore
Sound pollution from mining machinery
Destruction of habitat due to construction of mines
Usage of large amount of electrical energy
Air pollution by gases released from blast furnaces