Question

Chemistry - Class 7
a) The formula of a compound is AB. If the valency of B is 3, what will be the valency of A?
b) Baking soda is a white solid and has the formula NaHCO3. How many of each type of atoms are there in it?

Answer 1

1) The valency of A must be 3 . Since , the value of B is 3 and the molecular formula is AB , if the valency of A comes out to be 3 , it will fulfill the given condition . Valency is the combining capacity of an element .

When the molecular formula is AB , this means that the 3 electrons are gained completely by B ( as its valency is 3) and since no subscript as a number is added after A , the valency of A must be equal to B equal to 3 . This means that the three electrons gained by B are lose by A .

2) The number of atoms in a molecule of baking soda $\tt ( NaHCO_3)$ is :

• Na : 1 atom
• H : 1 atom
• C : 1 atom
• O : 3 atoms

The number written in the subscript gives the number of atoms in a molecule of that substance.