Classify the following as physical or chemical properties.
(a) The composition of a sample of steel is: 98% iron, 1.5% carbon and 0.5% other elements.
(b) Zinc dissolves in hydrochloric acid with the evolution of hydrogen gas.
(c) Metallic sodium is soft enough to be cut with a knife.
(d) Most metal oxides form alkalis on interacting with water.
Options (a) and (c) show physical properties. Options (b) and (d) show chemical properties.
(a) The composition of a sample of steel shows a physical property because steel is an alloy and alloy is a homogeneous mixture of two or more metals or of metallic elements with non-metallic. No new compound is formed.
(b) Such a reaction shows a chemical property because chemical reaction takes place between zinc and hydrochloric acid with the evolution of hydrogen gas and a compound zinc chloride is formed.
The chemical equation shows the following reaction:
Zn(s)+ 2HCI (dil)→ ZnCI2(aq) + H2(g)
(c) Cutting of metallic sodium shows a physical property because no new substance is formed in the process. It is just cutting a big portion of metal into a small portion.
(d) Such a reaction shows a chemical property because chemical reaction takes place between metal oxide and water to form metal hydroxide, which is a new substance.
M2O (s) (Metal oxide) + H2O (Z) (Water) → 2MOH (aq) (Metal hydroxide)