Question 2 Page 42 - Chapter 3 Class 9 - Atoms And Molecules

Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?

Answer

To find which one has more atoms, we’ll find the number of moles of both.

Since 1 mole of any substance has the same number of atoms, the element having more number of moles will have more atoms .

Let,

Given mass of Na = m n =100g

Given mass of Fe = m f =100g

We know that,

Molar mass of a substance = Atomic mass of the substance (in g)

Therefore, 

Molar mass of Na = M _n = 23g

Molar mass of Fe = M _f = 56g

Now,

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

For Na, = m _n /M _n

             = 100/23

             ≈  4.34 moles

For Fe, = m _f /M _f

             = 100/56

             ≈  1.78 moles

Since, Number of moles of Na > Number of moles of Fe .

100g of Na will have more atoms than 100g of Fe .