Question

What mass of Nitrogen, N₂, will contain the same number of molecules as 1.8g of water, H₂O?

Answer 1

Atomic mass of H2O is 18 grams

hence 1.8 gram H2O=1.8/18 moles=0.1 moles=0.1×6.022×10^23 molecules

for same number of N2 molecules we need 0.1 mole of N2

as 1 mole N2 has 28 gm mass

so 0.1 mole N2 will have=0.1×28 gram
=2.8 grams

hence we need 2.8 grams N2