how many molecules are in 18.02 g of water?

Question

how many molecules are in 18.02g of water?

 

Answer 1

Find the molecular weight (MW) of H₂O in g/mol.

 

MW = 2(1.01) + 16.00 = 18.02 g/mol

 

Divide the number of grams by the molecular weight in g/mol.  In this question, the two are the same number, so when you divide, you get 1.  That is the number of moles of H₂O in 18.02 g of H₂O.  So you have 1 mole of water, and 1 mole contains Avogadro's number of molecules, which is 6.02 x 10²³.