Question

Bell metal contains 80% copper the mass of bell metal which contains 1.5*10²⁰ atoms of copper is

Answer 1

According to Avogadro's constant, 1 mole of a any substance has exactly 6.022 × 10²³ atoms or molecules. 

Find the number of moles in the bell metal: 

If 6.022 × 10²³ atoms = 1 mole 

Then 1.5 × 10²⁰ = 1 ×1.5 x 10²⁰/6.022 × 10²³ 

= 0.00025 

moles molar mass of Cu is 64 

mass = moles × molar mass 

= 0.00025 mol × 64g/mol 

= 0.016 g 

Therefore 1.5×10²⁰ atoms of copper has a mass of 0.016 g 

This 80% of the piece of metal, weight of the mass is 100% 

= 100/80 × 0.016 = 0.02 g 

The piece of metal has a mass of 0.02 g