Reactivity of metals

4.1Variety of minerals

Each ore looks different in colour, structure, shape and texture because it contains different minerals. Minerals in the Earth's crust are of two kinds.

Natural compounds and the elements in them

Names of natural compounds: textbook Table 4.1, p. 125.

Showing that a compound is made of several elements (Activity 4.1)

Calcium carbonate (found as limestone, marble, chalk, calcite, coral and shells) gives carbon dioxide in two different ways. Carbon dioxide turns limewater cloudy.

The gas contains carbon and oxygen, and the solid left behind contains calcium, so calcium carbonate is a compound of three elements: calcium, carbon and oxygen.

Properties and uses of minerals

• Limestone (calcium carbonate): used for roads, buildings and table tops.
• Calcium oxide is basic, so it neutralises acidic soil.
• Silicon dioxide has a high melting point, so it is used to make glass laboratory apparatus.
• Lithium and cobalt minerals make long-lasting batteries for electric cars.

4.2Reactivity series of metals

Magnesium burns in air with a bright flame (a vigorous reaction). Iron only glows or changes colour slowly (a less vigorous reaction). Metal + oxygen always gives a metal oxide.

Activity 4.3: metals heated with oxygen

Oxygen is supplied by heating potassium manganate(VII) crystals. The metal powder sits on a porcelain plate in a boiling tube, separated from the crystals by glass wool.

Order of decreasing reactivity from this activity: magnesium > aluminium > zinc > iron > lead.

Position of carbon and hydrogen in the series

Carbon and hydrogen are non-metals, but they also react with oxygen (carbon + oxygen → carbon dioxide; hydrogen + oxygen → water). They are placed in the series by testing whether they can take oxygen away from a metal oxide. Removing oxygen from an oxide is reduction.

Hydrogen reduces iron(III) oxide, lead(II) oxide and copper(II) oxide, but cannot reduce aluminium oxide or zinc oxide. So hydrogen is more reactive than iron, lead and copper, and less reactive than aluminium and zinc.

Keeping reactive metals

Potassium and sodium react with oxygen and water vapour in the air, so they are kept under paraffin oil. Lithium batteries can explode when heated, so passengers are not allowed to keep them in luggage placed in aircraft.

4.3Extraction of metals from their ores

Tin, which Malaysia has mined for a long time, lies below carbon, so tin ore (tin(IV) oxide) is heated with carbon: tin(IV) oxide + carbon → tin + carbon dioxide.

Extraction of iron in a blast furnace

1. A mixture of concentrated iron ore (iron oxide), coke and limestone is fed in at the top.
2. A blast of very hot air is pumped in at the bottom.
3. Reactions at high temperature:
   • Coke burns: carbon + oxygen → carbon dioxide (and heat).
   • Carbon dioxide + carbon → carbon monoxide, a strong reducing agent.
   • Iron oxide is reduced: iron(III) oxide + carbon monoxide → iron + carbon dioxide (carbon works too).
   • Limestone decomposes: calcium carbonate → calcium oxide + carbon dioxide.
   • Calcium oxide removes the sand impurity: calcium oxide + silicon dioxide → calcium silicate (slag).
4. Both iron and slag are molten and run to the bottom. Slag is less dense, so it floats on the iron. Iron is tapped off into moulds, where it freezes as cast iron. The slag is used for the base of buildings and roads.

Mining issues in Malaysia

Poorly planned mining harms life locally and globally. Creative, innovative ideas support sustainable development. Coal, a mineral found in Malaysia, is mostly in Sarawak (about 80%).

Summary