Question

Question 18
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 1

(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 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.
$Zn\left(s\right)+2HCI\left(dil\right)\to ZnC{l}_2\left(aq\right)+H_2\left(g\right)$

(c) It is physical property because cutting with a knife does not form the new substance.

(d) It is chemical property as the new compound is being formed by the reaction of metal oxide and water.

$M_{2}O\left(s\right)+H_{2}O\left(l\right)\to 2MOH\left(aq\right)MetaloxideWaterMetalhydroxide$