What it does
An alloy is a metal mixed with other elements, melted together so the atoms mix. Most metal things around you are alloys, because pure metals are often too soft, rust too easily or melt too high. This page lets you mix your own:
- choose one of ten alloys: brass, bronze, old and lead-free solder, steel, stainless steel, duralumin, magnalium, 22 carat gold and dental amalgam,
- read the usual recipe, what it is used for and why,
- change the recipe with a slider for each element; numbers that don’t add to 100 % are scaled,
- set a batch mass to get the grams of each metal, the density by the mixing rule, the volume, and for gold the carat,
- push the top layers of atoms in a picture to see why a pure metal bends easily but an alloy resists,
- turn carats into per cent gold and grams of gold in a piece of jewellery.
It follows the Class 10 chapter on metals and non-metals (alloys) and the Class 8 topic of materials.
How readily each metal reacts, and so how it is extracted, is in the reactivity series lab; look up each element in the interactive periodic table, and see a thin layer of one metal put on another in the electroplating.
How to use it
- Choose the Alloy and type the Batch mass in grams.
- Move the sliders (or type per cent by mass). Back to the usual recipe resets them.
- Read the masses, the density working and, for gold, the carat.
- In Why alloys are harder, choose Pure metal or Alloy and press Push the top layers.
- In Gold carats, type a carat number and the mass of the jewellery.
A worked example
Brass, 65 % copper and 35 % zinc, batch 500 g:
- copper 0.65 × 500 = 325 g, zinc 0.35 × 500 = 175 g,
- density by the mixing rule: 1 ÷ (0.65 ÷ 8.96 + 0.35 ÷ 7.13) = 8.22 g/cm³, between copper (8.96) and zinc (7.13),
- the 500 g batch takes up about 60.8 cm³.
Gold: 22 carat means 22 parts gold in 24, which is 91.67 % (often stamped 917). A 10 g chain of it holds 9.167 g of pure gold.
Tips
- An alloy’s density is always between the densities of its metals (by this rule).
- Steel is iron with only a little carbon, yet much harder: the small carbon atoms sit in the gaps between iron atoms.
- Solder melts at a lower temperature than either tin or lead alone, which is why it is good for joining wires.
Check yourself
Four fresh questions each time: grams of zinc in brass, grams of gold in jewellery, the density of a two-metal alloy, and carbon in steel. Nothing is saved.
FAQ
Are these the exact recipes? No. Each alloy comes in many grades; the page uses typical round numbers so you can see how the sums work.
Is this from the NCERT book? It covers the same topic with fibub’s own examples. fibub is not part of NCERT.
Where the numbers come from
- Element densities are rounded handbook values at room temperature (general facts); alloy recipes are typical rounded ranges from general chemistry teaching, not a specification. The mixing rule 1/ρ = Σ w/ρ assumes the volumes simply add, which is an approximation. 24 carat = pure gold. Written for fibub.
- Checked against Python: brass of 65 % copper and 35 % zinc comes out at 8.2215 g/cm³; 500 g of it holds 175 g of zinc; 22 carat is 91.67 % gold; every recipe's density lies between those of its metals.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.