Question

calculate the number of molecules and atom in, 18 g of water

Answer 1

molecules

6.022×10^23

atoms

3

Answer 2

no of molecules = avagadro No. * given mass/molecular mass

molecular mass of H₂O = 1 *2 + 16 = 18 g

given mass = 18 g

avagadro number = 6.022 * 10²³

given mass/molecular mass = 18/18 = 1

=>1 * 6.022 * 10²³ = 6.022 * 10²³ = No. of molecules

no of atoms = No. of molecules * 3(as there are 3 atoms in H₂O)

which is

6.022 * 10²³ * 3 = 18.066 * 10²³ or 1.8066 * 10²⁴

which is also

3 moles of atoms

1 mole of molecules