Question

calculate the number of atoms present in 4g of calcium (At.mass of calcium =40g

Answer 1

Calculate the number of atoms present in 4g of calcium
(At.mass of calcium =40g
at.massof calcium/atoms preasent=40/4=10

Answer 2

The molar mass (i.e. the mass of one mole of particles) of Calcium is 40g. This means that there are 6.023 X 1023 atoms of calcium in 40g of calcium. Thus

Number of atoms in 40g of calcium = 6.023 X 1023

number of atoms in 1g of calcium = (6.023 X 1023) / 40

number of atoms in 4g if calcium = (6.023 X 1023 X 4) / 40

= 6.023 X 1022

So, the number of atoms in 4g of Ca are 6.023 X 1022. We have to calculate the mass of sodium which contains the same number of atoms as 4g of Ca. Now the molar mass of sodium is 23g. This means that there are 6.023 X 1023 atoms of sodium in 23g of sodium. Thus

Mass of 6.023 X 1023 atoms of sodium = 23g 

Mass of 1 atom of sodium = [23 / (6.023 X 1023)]

Mass of 6.023 X 1022 atoms of sodium = [23 X (6.023 X 1022)] / (6.023 X 1023)

= 2.3g