NCERT Question 9 (a) - Chapter 3 Class 9 - Atoms And Molecules

What is the mass of:

(a) 0.2 mole of oxygen atoms?

Answer

We know that,

Number of moles of a substance = Given mass of the substance / Molar mass of the substance

Therefore,

Mass of the substance = Number of moles x Molar mass of the substance

(a) 0.2 mole of oxygen atoms

Given mass of O = m = ?

Molar Mass of O = M = 16g

Number of moles = n = 0.2 = 2/10

We know that,

Mass of the substance = Number of moles x Molar of the substance

 m = n x M

     = (2 /10) x 16

     = 32 /10

     = 3.2g