Chapter 3: Atoms and Molecules

Mass of one mole of Aluminium atom = {13 × mass of each electron + 13 × mass of each proton + 14 × mass of each neutron} × Avogadro’s constant.

We know, if atoms convert into ions, only transfer of electrons takes place, in Al+3 ion, Aluminium atom loss three electrons,

So,

Mass of Al+3 ={10× mass of each electron +13 × mass of each proton + 14 × mass of each neutron} Avogadro’s constant

Now,

You see mass of aluminium atom is greater than aluminium ion by 3 electrons

Difference in mass =Mass of Aluminium atom -mass of aluminium ion

= 3 × mass of each electron x Avogadro’s constant .

= 3 × 9.1 × 10^-28x 6.023 x 10²³

=27.3 x 10^-28 x 6.023 x 10²³ g

=164.4 x 10^-5 g

= 1.644 x 10^-3 g

= 0.0016 g

Mass of silver = m g

Mass of gold = m /100g

Number of atoms of silver =  Mass/ Atomic mass X NA

= m /108NA   Number of atoms of gold

= m/ 100 X197

Ratio of number of atoms of gold to silver =  Au : Ag

= m/ 100 X 197 X NA : m/ 108 NA

= 108 : 100×197

= 108 : 19700  = 1 : 182.41

Solution coming soon.