Question

How many grams are in 7.62 X 1017 molecules of oxygen?

Answer 1

The  number   of  grams  that are  in 7.62 x10^17    molecules  of oxygen is 4.064 x10^-5  grams

   calculation

by  use of Avogadro  constant  find  number of  moles  in  7.62 x10^-17
that is  1  mole =  6.02 x10^23  molecules
               ?       =    7.62 x10 ^17  molecules

cross  multiply

(1mole x 7.62 x10^17)/6.02  x10^ 23  =  1.27 x10^-6  moles

mass =  mole x  molar  mass

molar mass  of oxygen  molecule = 16 x2=32g/mol

mass =  11.27 x10^-6 moles x  32 g/mol  =  4.064  x10^-5  grams