Question

calculate the number of molecules present in A) 0.9g of water B)1.7g of ammonia.

Answer 1

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a)Gram-molecular mass of water=18g

Number of moles in 0.9g of water =0.918

⇒0.05

Number of water molecules in one mole of water=6.02×1023

Number of molecules of water in 0.05 moles

⇒0.05×6.02×1023

⇒3.010×1022

As one molecule of water contains one oxygen atom ,so number of oxygen atoms in 3.010×1022 molecules of water =3.010×1022

b)Molecular mass of NH3 is 17g/mol

No. of moles of ammonia =1.7/17 =0.1 mole

No. of neutrons in one molecule of NH3 is 7 because H has no neutron.

No. of neutrons in 0.1 mole of NH3 =7×0.1×6.022×10^23

4.2154×10^23 neutrons

Hope it helps