Category: Metals

Why does copper turn green after some time when exposed to the atmosphere?

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Copper reacts with oxygen in the air to form a copper(II) oxide coating.
2Cu (s) + O2 (g) –> 2CuO (s)
Copper(II) oxide reacts with moist carbon dioxide to form a mixture of copper(II) carbonate and copper(II) hydroxide. The green copper(II) carbonate causes the green appearance of copper.
2CuO (s) + H2O (l) + CO2 (g) –> CuCO3 (s) + Cu(OH)2 (s)

The mixture of copper(II) carbonate and copper(II) hydroxide forms a protective coating, preventing further corrosion of copper underneath the coating.
Whereas in the corrosion of iron or steel, the coating of rust (hydrated iron(III)oxide) flakes off easily, exposing the iron/steel underneath, causing corrosion of iron/steel to continue until the whole piece of iron/steel is corroded to iron(III)oxide.

Describe, with the help of chemical equations, the reactions in the blast furnace which lead to the production of molten iron.

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Coke reacts with oxygen in the air to form carbon dioxide.

C (s) + O2 (g) –> CO2 (g)

Coke then reacts with carbon dioxide to form carbon monoxide.

C (s) + CO2 (g) –> 2CO (g)

Carbon monoxide reduces haematite to form molten iron and carbon dioxide.

Fe2O3 (s) + 3CO (g) –> 2Fe (l) + 3CO2 (g)

The action of heat on metals and metal carbonates

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Based on the data given, suggest which 2 were the metals and which 2 were the metal carbonates. Explain your answers.

Metals: A and D
Metal carbonates: B and C

Explanation:

Metals, when heated, will be oxidized by oxygen in the air to form metal oxides. The oxygen gained to form the oxide will cause the mass of the product formed to be higher. Mass increase for solids A and D after heating, so these two are metals.
Metal carbonates, when heated, can decompose to form metal oxides and carbon dioxide. The carbon dioxide formed escape to the surroundings, causing the mass of the solid product formed to be smaller.
The mass of B decreased after heating, so it must be one of the metal carbonates.
The mass and appearance of C remained unchanged, so it must be the other metal carbonate, which is not decomposed by the heat.

List down the metals reactivity series, from most reactive metal to the least reactive metal.

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Potassium, (most reactive)
Sodium,
Calcium,
Magnesium,
Aluminium,
(Carbon),
Zinc,
Iron,
Tin,
Lead,
(Hydrogen),
Copper,
Silver,
Gold,
Platinium (least reactive)

Use this mnemonic to help u remember.
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Give 3 advantages of recycling metals.

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It helps to reduce pollution. Extraction of metals from their ores produces much more air, land and water pollution compared to recycling of metals.

It conserves energy resources. Extraction of metals from their ores uses up much more energy compared to recycling of metals.

It conserves limited land resources. Metal mining and smelting processes use up large area of land. Recycling metals reduces the need for these metal mines, and free up the land for alternative uses.

Why is there a need to recycle metals?

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Metals are finite resources.

With the increasing demand for metals, our metal reserves will not last much longer.

Hence, there is a need to recycle metals to conserve the metal resources.

Recycling metals also use up less energy and produce fewer pollutants than extracting metals from their ores.

Explain, using structure and bonding, why alloys are stronger and harder than pure metals.

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Pure metals consist of a lattice of positive ions, arranged in regular pattern, surrounded by a sea of delocalised electrons. When a force is applied, the layers of positive ions slide over one another easily, without disrupting the metallic bonding. This makes the pure metal soft and malleable.

An alloy is a mixture of a pure metal with other elements. The atoms of the added element have a different size from those of the pure metal. This breaks up the regular arrangement of atoms in the pure metal. When a force is applied, the atoms of different sizes cannot slide over one another easily. This makes the alloy stronger and harder.