Question

the atomic mass of Calcium is 40 u . what will be the no. of atoms in 0.4 u of Calcium

Answer 1

Hi there !!!

Given mass = 0.4 u

Molar mass = 40 u
No: of moles = Given mass / Molar mass
= 0.4 / 40
= 0.01 moles

No: of atoms = No: of moles x Avogadro no:
= 0.01 × 6.022 × 10²³
= 0.06022× 10²³ atoms

Answer 2

40u contains 1 mole Ca 
0.4u contains (0.4/40 moles) Ca = 1/100 moles
1 mole of Ca contains 6.02*10²³ atoms
so 0.01 mole of Ca contains 6.02*10²¹ atoms