The simplest technique in the chapter, and the one you almost always use first when a mixture has several parts.
The property being used
DefinitionMagnetic attraction is used to separate magnetic substances from non-magnetic substances.
Magnetic substances such as iron and steel are attracted to a magnet. (Steel is a mixture of iron and other elements — which is why it is magnetic too.) Substances such as plastic, paper, glass, rubber and sulfur are non-magnetic and are left behind.
Iron filings and sulfur
On the magnet—
Left in the dish—
Only the iron moves. Sulfur is non-magnetic, so the magnet passes straight over it.
Where it is used: the scrapyard
In Singapore, scrap metal is one of the many waste materials generated. Scrap metal is a mixture of metals such as aluminium, copper and iron. Iron is magnetic, so passing a strong magnet over the scrap removes it. The iron obtained can then be reused or recycled, which helps to reduce waste.
Removed by the magnet
Left behind
steel bolts and nuts · iron bar · steel pipe · iron chain
glass mirror · rubber tyre · plastic car parts such as a bumper
The trap: not all metals are magnetic
Aluminium and copper are metals, but they are not magnetic. A magnet passed over scrap metal removes only the iron and steel — the aluminium and copper stay behind with the plastic and glass. If a question asks whether a magnet can separate copper from aluminium, the answer is no: neither is magnetic, so there is no difference to exploit.
Why this technique usually goes first
Magnetic attraction needs no water, no heat and no waiting, and it takes its target out cleanly and dry. In a multi-step separation such as iron filings + salt + sawdust, use the magnet before you add water — otherwise you have to fish wet iron filings out of a solution.