INTRODUCTION/ DEFINITIONS.
The law of conservation mass is based on the following postulate of Dalton’s Atomic theory.
“Atoms can neither be created nor destroyed during a physical change or a chemical reaction.”
Atomic mass unit may be defined as :
The mass of one-twelfth (1/12) of the mass of one atom of carbon taken as 12 u
Molecules are represented in terms of symbols of constituting atoms and it is known as chemical formula.
• Positive ion migrating towards cathode on passing electric current is known as cation.
• Negative ion migrating towards anode on passing electric current is known as anion.
1/12 of the mass of carbon atom taken as 12 u is used as a reference for the atomic masses of the elements.
Avogadro’s number is the number of particles (atoms, ions, molecules etc.) present in one mole of any substance. It is denoted either as NA or as NQ.
The number is also called Avogadro’s constant because its value is fixed (6.022 x 1023) irrespective of the nature of the particles.
The total mass of the products in a physical change or a chemical reaction is equal to the total mass of the reactants that have combined.
The law may also be stated in another form. The mass can neither he created nor destroyed in a physical change or a chemical reaction.
In other words, the mass remains unchanged or conserved in a chemical reaction. The law is also known as the Law of Indestructibility of Matter.
An atom is always neutral in the sense that it does not carry any charge. An ion carries either positive charge (cation) or negative charge (anion).
Ammonium (NH4)+ ion is a polyatomic cation while sulphate (SO4)2- ion is a polyatomic anion.
Hydrogen gas is diatomic in nature (H2) while helium gas is monoatomic (He).
Baking powder is the commercial name of the compound. Its chemical name is sodium hydrogen carbonate and the chemical formula is NaHCO3
All atoms of a particular element are identical in every respect. This means that they have same mass, same size and also same chemical properties.”