Question

Bell metal contains 80% copper. the mass of bell metal which contains 1.5×10^20 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 × 10^20  = 1 ×1.5 x 10^20/6.022 × 10²³
                              =     0.00025 moles 
molar mass of Cu is 64
     
mass = moles × molar mass
         =  0.00025 mol × 64g/mol
         = 0.016 g
Therefore 1.5×10^20 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