Platinum (Pt): Comprehensive Study Guide for JEE/NEET/CBSE

Introduction: Why Platinum Matters

Platinum (Pt) is a rare, dense, ductile, malleable, highly unreactive, and valuable precious metal. Its exceptional corrosion resistance, high melting point, and catalytic properties make it indispensable in various high-technology applications. Its significance extends from critical industrial processes to advanced medical treatments and luxury goods.

CBSE/JEE Quick Revision Notes

Symbol: Pt
Atomic Number: 78
Atomic Mass: 195.084 u
Group: 10 (formerly VIIIB in older classifications)
Period: 6
Block: d-block
Classification: Transition Metal, Noble Metal
Physical State at STP: Solid
Colour: Silvery-white
Density: 21.45 g/cm³ (one of the densest metals)
Melting Point: 1768.3 °C
Boiling Point: 3825 °C
Characteristic: Highly resistant to corrosion, oxidation, and chemical attack (inert).

Electron Configuration & Bonding Behavior

Ground State Electron Configuration: [Xe] 4f¹⁴ 5d⁹ 6s¹
- Note: This configuration is an exception to the Aufbau principle, where an electron from the 6s orbital is promoted to the 5d orbital to achieve a more stable electronic configuration (pseudo-filled d-subshell).
Common Oxidation States:
- +2: Often forms square planar complexes (e.g., [PtCl₄]²⁻).
- +4: Most stable and common oxidation state, forms octahedral complexes (e.g., [PtCl₆]²⁻).
- Other oxidation states (+1, +3, +5, +6) are rare but exist in specific compounds.
Bonding: Platinum forms strong covalent bonds. Its vacant d-orbitals readily accept electron pairs from ligands, leading to extensive complex formation.

Crucial Chemical Reactions

Platinum’s high inertness means it reacts with very few reagents, primarily under specific, often harsh, conditions.

1. Reaction with Aqua Regia

Platinum does not react with single acids (like nitric acid or hydrochloric acid) but dissolves in aqua regia (a mixture of concentrated nitric acid and hydrochloric acid, typically in a 1:3 molar ratio). This reaction is crucial for its refining and processing.

3Pt(s) + 4HNO₃(aq) + 18HCl(aq) → 3H₂[PtCl₆](aq) + 4NO(g) + 8H₂O(l) Here, nitric acid acts as an oxidizing agent, and hydrochloric acid stabilizes the Pt(IV) ions by forming the hexachloroplatinate(IV) complex ion [PtCl₆]²⁻.

2. Reaction with Halogens

Platinum reacts with halogens at elevated temperatures to form halides.

With Chlorine: Pt(s) + 2Cl₂(g) → PtCl₄(s) (at approx 250-300 °C)
With Fluorine: Platinum reacts vigorously with fluorine to form platinum fluorides, often in higher oxidation states.

3. Reaction with Molten Alkalis or Peroxides

Under extreme conditions (high temperatures with molten alkalis or alkali peroxides), platinum can be attacked. This reaction is generally not encountered in standard high school curricula in detail but indicates platinum’s ultimate reactivity limit.

Industrial and Biological Importance

Industrial Importance

Catalysis: Platinum is a premier catalyst.
- Automotive Catalytic Converters: Converts harmful gases (CO, NOx, unburnt hydrocarbons) into less noxious substances (CO₂, N₂, H₂O).
- Chemical Industry: Used in the production of nitric acid (Ostwald process), sulfuric acid, and in hydrogenation/dehydrogenation reactions in organic synthesis.
- Petroleum Refining: Catalyst for cracking and reforming processes to produce higher-octane gasoline.
Jewellery: Valued for its rarity, natural white luster, durability, and resistance to tarnish.
Electronics: Used in electrical contacts, electrodes, thermocouples, and hard disk coatings due to its excellent conductivity and corrosion resistance.
Laboratory Equipment: Platinum crucibles, electrodes, and dishes are used in chemistry labs for high-temperature applications due to their inertness and high melting point.
Medical & Dental: Used in pacemakers, dental fillings, and as an electrode material in some medical devices.

Biological Importance

Chemotherapy Drugs: Several platinum-based coordination compounds are potent anticancer agents. The most notable example is Cisplatin (cis-diamminedichloroplatinum(II), cis-[Pt(NH₃)₂Cl₂]), which inhibits DNA replication in rapidly dividing cancer cells.
Bio-inertness: In its metallic form, platinum is largely bio-inert and non-toxic, making it suitable for implants. However, certain platinum compounds can be toxic or cause allergic reactions.