Question

Calculate the no of atoms of oxygen present in 120g of nitric acid

Answer 1

Here, first we will calculate the number of moles of HNO3 that are present in 120 g of HNO3. The molar mass of HNO3 is 63g. Therefore

63g of HNO3 = 1 mole of HNO3

1g of HNO3 = (1 / 63) moles of HNO3

Therefore 120g of HNO3 = (120 / 63) moles of HNO3

= 1.905 moles of HNO3

Now 1 mole of a substance contains 6.023 X 1023 molecules of the substance. Therefore

1 mole of HNO3 = 6.023 X 1023 molecules of HNO3

So 1.905 moles of HNO3 = 1.905 X 6.023 X 1023 molecules of HNO3

= 1.147 X 1024 molecules of HNO3

Now 1 molecule of HNO3 contains 3 atoms of oxygen. Therefore 1.147 X 1024 molecules of HNO3 will contain

= 3 X 1.147 X 1024 atoms of oxygen

= 3.442 X 1024 atoms of oxygen

Answer 2

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