Metal and Alloys (Iron)

Question 1

What are the key properties of metals?

Answer 1

• Good conductors of electricity and heat due to delocalized electrons.
• Malleable, ductile, and shiny.
• Form cations by losing electrons and react with oxygen to form basic oxides.

Question 2

What is an alloy, and how does it differ from a pure metal?

Answer 2

• An alloy is a mixture of a metal with other elements, enhancing properties like strength or resistance to corrosion.
• Alloys often prevent metal ions from sliding past each other, making them stronger than pure metals.

Question 3

Give examples of alloys and their uses.

Answer 3

• Duralumin (aluminum, copper, magnesium): Aircraft construction.
• Bronze (copper, tin): Statues, bearings.
• Stainless steel (iron, chromium, nickel): Cookware, cutlery, chemical plants.

Question 4

What is the significance of iron on Earth?

Answer 4

• Iron is the most common element in Earth’s core and the fourth most abundant in the crust.
• It is widely used in construction and steel production, accounting for 95% of all metals used annually.

Question 5

How is iron extracted in a blast furnace?

Answer 5

1. Main ore: Haematite Iron(iii) oxide (Fe₂O₃).
2. Process:
   - Haematite is mixed with coke and limestone in the furnace.
   - Hot air burns coke, forming carbon monoxide, which reduces Fe₂O₃ to molten iron.
   - Limestone removes impurities by forming slag (calcium silicate).
3. Equations
   - Fe2O3 + 3CO > 2Fe + 3CO2 (Reduction)
   - CaCO3 > CaO + CO2 (Decomposition of limestone)

Question 6

What are the different forms of iron, and how are they used?

Answer 6

• Cast iron: High carbon (4-5%), brittle; used in stoves, pipes, and manhole covers.
• Wrought iron: Nearly pure, malleable; used for gates and ornamental work.
• Steel: Iron-carbon alloy (0.1%-1.5% carbon); widely used in construction, vehicles, and tools.

Question 7

Why is steel more widely used than pure iron?

Answer 7

• Steel has improved strength and flexibility due to its carbon content and alloying elements.
• Pure iron is too soft and lacks durability for industrial applications.

Question 8

What is stainless steel, and what makes it resistant to corrosion?

Answer 8

• Stainless steel is an alloy of iron, chromium (15%), nickel (4%), and carbon.
• Chromium reacts with oxygen to form a thin, stable oxide layer, preventing further oxidation (corrosion).

Question 9

What is the role of slag in the blast furnace?

Answer 9

• Slag, formed by the reaction of silica impurities with calcium oxide, floats on molten iron.
• It prevents the furnace from clogging and is later used in road construction.

Question 10

What is the environmental alternative to iron production using coke?

Answer 10

Direct Iron Reduction (DIR): Uses natural gas to reduce iron ore to sponge iron, avoiding coke.
- Reaction
2CH4 + O2 > 2CO + 4H2 (Partial oxidation of natural gas)
Fe2O3 + CO +2H2 > 2Fe + CO2 + 2H2O

Question 11

How does rusting of iron occur, and how can it be prevented?

Answer 11

1. Rusting process:
   - Iron reacts with water and oxygen to form hydrated iron(III) oxide (Fe2O3.xH2O)
   - Requires both water and oxygen, accelerated by salt or acid.
2. Prevention methods:
   - Coating with paint or plastic.
   - Galvanizing with zinc (sacrificial protection).
   - Using stainless steel.

Question 12

What is the composition and application of duralumin?

Answer 12

• Composition: Aluminum (94%), copper (4%), magnesium (1%), with small amounts of manganese and silicon.
• Application: Aircraft construction due to its strength-to-weight ratio.

Question 13

How is carbon removed during steel production?

Answer 13

`- By blowing oxygen through molten iron to oxidize carbon into carbon dioxide.
- Impurities like sulfur and phosphorus are removed using basic refractories (lime).

Question 14

What is sacrificial protection, and where is it used?

Answer 14

• More reactive metals like zinc or magnesium are attached to iron/steel structures to prevent rusting.
• Used in ships, underwater pipelines, and oil rigs.