Gold (Au) and platinum (Pt) are ideal for making jewellery because they possess a rare combination of properties: chemical inertness (unreactivity), brilliant lustre, high malleability and ductility, and resistance to tarnishing. Being at the bottom of the activity series, they do not react with air, water, or most acids under normal conditions, ensuring jewellery retains its beauty indefinitely.
Gold and platinum are at the bottom of the activity series — most chemically unreactive metals.
They do not react with air, water, or dilute acids — no tarnishing or corrosion.
Both are highly malleable (beaten into sheets) and ductile (drawn into wires).
Gold dissolves only in aqua regia (3:1 conc. HCl : conc. HNO₃).
Gold has density 19.3 g/cm³ and melting point 1064°C.
Platinum has density 21.4 g/cm³ and melting point 1768°C.
Both are hypoallergenic — safe for prolonged skin contact.
24 karat gold is pure; 22 karat (91.7%) and 18 karat (75%) are used in jewellery.
Gold and platinum are at the bottom of the activity series (reactivity series):
Activity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au > Pt
Being at the bottom means:
This chemical stability means jewellery made from these metals retains its appearance forever.
Malleability — can be beaten into thin sheets without cracking. Gold can be beaten into sheets 0.1 µm thin (gold leaf).
Ductility — can be drawn into thin wires. 1 gram of gold can be drawn into 2 km of thin wire.
Lustre — shiny and attractive natural appearance. Gold: yellow metallic shine. Platinum: silvery-white shine.
Hardness — sufficiently hard to hold shape but workable. Pure gold is soft (alloyed with Cu or Ag for strength — 22 karat, 18 karat).
High density — gives a sense of quality and value. Gold: 19.3 g/cm³. Platinum: 21.4 g/cm³.
High melting point — can withstand heat during crafting. Gold: 1064°C. Platinum: 1768°C.
Gold purity: • 24 karat = pure gold (100%) • 22 karat = 91.7% gold (mixed with Cu/Ag for hardness) • 18 karat = 75% gold
Platinum in jewellery: • Naturally white — no plating needed • Stronger than gold — better for holding gemstones • Hypoallergenic — ideal for sensitive skin
Gold and platinum are suitable for jewellery because: (1) They are chemically unreactive — at the bottom of the activity series, so they do not tarnish, rust, or corrode; (2) They have brilliant natural lustre; (3) They are highly malleable and ductile — can be shaped easily; (4) They are hypoallergenic and non-toxic; (5) They retain their appearance permanently.
Gold and platinum are at the very bottom of the activity series, making them the least reactive metals. This means they do not react with air, water, dilute acids, or most chemicals under normal conditions, which is why jewellery made from them lasts indefinitely.
Gold is extremely unreactive under normal conditions. It only dissolves in aqua regia — a mixture of concentrated HCl and concentrated HNO₃ in a 3:1 ratio. It does not react with oxygen, water, dilute acids, or alkalis.
Pure gold (24 karat) is too soft for jewellery and scratches easily. It is alloyed with small amounts of copper or silver to increase hardness. 22 karat gold (91.7% pure) and 18 karat gold (75% pure) are commonly used in jewellery making.
Gold has a yellow colour and density of 19.3 g/cm³, while platinum is silvery-white and denser at 21.4 g/cm³. Platinum is harder than gold, making it better for holding gemstones. Both are chemically unreactive and hypoallergenic, but platinum is naturally white and does not need plating.
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