Question

Question 21

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.

Answer 1

(a) Yes, rust is iron oxide $\left(F{e}_2{O}_3\right)$. Thus, rust and iron are not the same substance.
(b) No, rusting of iron is a chemical change because in this reaction, a new substance, rust (iron oxide) is formed. It cannot be reversed by any simple method.
(c) Yes, rusting of iron is a chemical change. During the rusting of iron, it combines with the oxygen in the presence of water (moisture) to form a new compound ‘iron oxide’. This iron oxide is a rust.
Iron + Oxygen + Water $⟶$ Iron Oxide
(From damp air) (Rust)
It is a permanent change which cannot be reversed back. So, rusting of iron is a chemical change.
(d) Burning of paper and cooking of vegetables are similar examples of chemical change