question_answer 39)

  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.

Answer:

  (a) It is a physical property as no new compound is formed because steel is an alloy and alloy is a homogeneous mixture of two or more metals or of metallic elements with non-metallic elements. (b) It is 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. (c) It is physical property because cutting with knife does not form new substance. (d) It is chemical property as new compound is being formed by the reaction of metal oxide and water.