Question

calculate the number of atoms in 0.05g of hydrogen atoms?

Answer 1

First thing to do is to find no. of moles in 0.05g of HOH

molecular weight of HOH =18 g mol^-1

n = weight of HOH/ molecular weight=0.05/18=2.78*10^-3 mol

Then no. of molecules of HOH in 2.78*10^-3 mol is

No. of molecule= n* Avogadro no.= 2.78*(10^-3) * 6.022*(10^23)=16.74*10^20 molecules of HOH

Now move towards question, its given no. of atom and not no. of molecules. Hence for every molecule of HOH there are three atoms, two of H and one of O.

Hence final answer is 3(16.74)*10^20= 50*10^20=5*10^21

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Answer 2

1gm = 6.023×10²³

then , 0.05 g = 6.023×10²³ × 5/100

= 6.023 × 10²¹ × 5

= 30.115 × 10²¹ atom