Question

Using atomic masses, If a certain batch of D2O has a purity of 99.75 weight %, what is its purity in atom (actually molecule) %

Answer 1

I'm not sure I know what the question is asking. First, 99.75 weight % of what? I will assume that means 99.75% w/w D2O in H2O. So in a 100 g same of the water,
99.75g D2O and 0.25g H2O

mols D2O = 99.75/molar mass D2O
molecules D2O = ? x 6.023E23

mols H2O = 0.25/molar mass H2O = z
molecules H2O = z*6.023E23

Total # molecules = sum of D2O and H2O

Then molecule% D2O =
[(molecules D2O/total molecules)]*100 = ?

molecule % H2O =
[(molecules H2O/total molecules)]*100 = ?