Question

What is the no. Of moles of O-atom in 126 amu of HNO₃

Answer 1

Answer: We have

1 amu = 1.66 x 10^-24 grams

126 amu = 126 x 1.66 x 10^-24

              = 209.16 x 10^-24 grams

1 mole HNO₃ = 63.01 g

Hence 209.16 x 10^-24 grams = 3.32 x 10^-24 moles

1 mole = 6.023 x 10²³ molecules

hence 3.32 x 10^-24 moles = 19.99 x 10²³  molecules

1 molecule of HNO₃ contains 5 atoms.

Hence, 19.99 x 10²³  molecules = 99.96 x 10²³ atoms

Therefore, 126 amu of HNO3 contains 99.96 x 10²³ atoms.