PRELIMS

Alloys and Metal Compounds

Alloys are metallic solid mixtures that improve the physical properties of their constituent elements.

Common Alloys and Their Compositions

• Brass: Composition: Cu (70%) + Zn (30%). Primary Uses: Making utensils.
• Bronze: Composition: Cu (90%) + Sn (10%). Primary Uses: Coins, bells, utensils.
• German Silver: Composition: Cu + Zn + Ni (60:20:20). Primary Uses: Making utensils (Note: No silver!).
• Rolled Gold: Composition: Cu (90%) + Al (10%). Primary Uses: Cheap ornaments.
• Gun Metal: Composition: Cu + Sn + Zn + Pb (88:10:1:1). Primary Uses: Gun barrels, gears, bearings.
• Dutch Metal: Composition: Cu (80%) + Zn (20%). Primary Uses: Artificial ornaments.
• Monel Metal: Composition: Cu (70%) + Ni (30%). Primary Uses: Acid-resistant containers.
• Solder: Composition: Pb (50%) + Sn (50%). Primary Uses: Soldering.
• Magnalium: Composition: Al (95%) + Mg (5%). Primary Uses: Aeroplane frames.
• Duralumin: Composition: Al + Cu + Mg + Mn (94:3:2:1). Primary Uses: Aeroplane parts, utensils.
• Type Metal: Composition: Sn + Pb + Sb (5:80:15). Primary Uses: Printing industry.
• Stainless Steel: Composition: Fe + Cr + Ni + C (75:15:10:0.05). Primary Uses: Surgical cutlery, utensils.
• Nickel Steel: Composition: Fe (95%) + Ni (5%). Primary Uses: Electrical wire, auto parts.
• Nichrome: Composition: Ni + Cr + Fe (60:15:25 approx). Primary Uses: Heating elements (electric irons, heaters) due to high resistance and heat resistance.
• Invar: Composition: Fe (64%) + Ni (36%). Primary Uses: Very low thermal expansion — pendulum rods, measuring tapes, precision instruments.
• Alnico: Composition: Al + Ni + Co + Fe. Primary Uses: Making strong permanent magnets.

Amalgam

An alloy in which one of the component metals is Mercury (Hg). (e.g., Sodium Amalgam).

Important Compounds and Their Uses

1. Ferrous Oxide (FeO): Green glass; ferrous salts.
2. Ferric Oxide ( ): Electroplating and ferric salts.
3. Ferrous Sulphate ( ): Dye industry; Mohr's salt.
4. Iodine ( ): Antiseptic; making Tincture of Iodine.
5. Bromine ( ): Dye industry; laboratory reagent.
6. Chlorine ( ): Bleaching powder; Mustard gas.
7. Hydrochloric Acid (HCl): Formation of Aqua Regia ( ).
8. Sulphuric Acid ( ): Petroleum purification; Lead batteries; reagent.
9. Sulphur Dioxide ( ): Oxidants/reductants; bleaching agent.

UPSC Relevance

Alloy compositions and common compounds are frequently tested in "Science in Daily Life" context.

• Common Trap: German Silver (contains Copper, Zinc, Nickel) does not contain Silver.
• Aerospace Materials: The importance of Magnalium and Duralumin due to their strength-to-weight ratio.
• Chemistry in Warfare: Identification of gases like Mustard gas (related to Chlorine).
• Solvents: The composition of Aqua Regia (used to dissolve noble metals like Gold).