Question

calculate the number of molecules in 45 gram of water

Answer 1

45 grams / 1 Mol H2O = 18.0152 g/mol

45 / 18.0152 = about 2.5 mols

2.5 mols x Avogadro's number(6.0221415 × 10^23) = Molecules in 45 grams H2O

Answer 2

given mass =m=45g
molar mass if water =M=18u
no.of moles=n=?
m=M×n
45=18×n
45/18=n
n=2.5