Question

Active mass of 5g CaO:
A.56
B.1
C.3.5
D.2

Answer 1

Basically, active mass is the concentration of the portion of a dissolved electrolyte that is dissociated into ions and is further capable of carrying the electric current. It is the concentration of the reacting substance which is usually expressed in moles per liter.

Complete step by step answer:
Active mass is also known as molar concentration or molarity. So, for a reactant A, the active mass would be given by:
$[A] = \dfrac{{mass\,of\,A}}{{molecular\,weight \times volume}}$
Basically, active mass is the amount of mass which is taking part I a reaction and that is further considered as the effective concentration of the substance. It is the concentration of the substance that is generally expressed in moles per litre. But the active mass in solids is always equal to one and hence the active mass of CaO will be 1g.
Hence, option B is correct.

Additional information:
Calcium oxide i.e. quicklime is an alkaline substance and it is believed that it is one of the oldest chemicals known to the human race. It is also known as burnt lime or lime. It can be prepared by thermal decomposition of materials like limestone or seashells that contain calcium carbonate in a lime kiln. The process that is used to prepare burnt lime is known as calcination. Further, calcium carbonate undergoes calcination and the products formed are burnt lime and carbon dioxide. The reaction is as shown:
$CaC{O_3} \to CaO + C{O_2}$

Note: Calcium oxide is widely used for medical purposes and insecticides. It also finds its application in manufacturing of cement, paper and high-grade steel. Moreover, lime is used as a reagent in labs for dehydration, precipitation reaction etc. It is the cheapest ingredient which is important in the manufacturing of caustic soda.