If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust.
(a) Do you think rust is different from iron?
(b) Can you change rust back into iron by some simple method?
(c) Do you think formation of rust from iron is a chemical change?
(d) Give two other examples of a similar type of change.
(a) Yes. Rust is iron oxide (Fe2O3) which is not same as Iron (Fe). Both are different substance.
(b) No. Rusting of iron is a chemical change resulting in the formation of new substance Iron oxide as product. It can’t be reversed by any simple method.
(c) Yes, rusting of iron is a chemical change. Iron combines with oxygen in presence of water to form a new substance ‘iron oxide’. The iron oxide is rust.
Iron (Fe) + Oxygen (O2, from the air) + water (H2O) —> rust (iron oxide Fe2O3)
It can’t be reversed. Hence, Rusting is a chemical change.
(d) Examples of similar type of chemical change are:
i) Burning of magnesium ribbon to form magnesium oxide.
ii) Souring of milk.