Ncert Solutions Chemistry Class 11th Chemistry Class 11th Structure of Atoms

(i) Calculate the total number of electrons present in one mole of methane.

(ii) Find (a) The total number and (b) The total mass of neutrons in 7 mg of ¹⁴C. (Assume that mass of a neutron = 1.675 × 10^-27kg).

(iii) Find (a) The total number and (b) The total mass of protons in 34 mg of NH₃ at STP. Will the answer change if the temperature and pressure are changed?

5 Views | Posted 3 months ago

1 Answer

Answered by

alok kumar singh | Contributor-Level 10

3 months ago

(i) One mole of methane (CH₄) has = 6.022 × 10²³molecules
No. of electrons present in one molecule of CH₄ = 6 + (4 x 1) = 10
No. of electrons present in 6.022 × 10²³ molecules of CH₄ = 6.022 × 10²³ × 10
= 6.022 × 10²⁴ electrons

(ii)  (a) Calculation of total number of carbon atoms
           Gram atomic mass of carbon (C-14) = 14 g = 14 × 10³ mg
            14 g or 14 × 10³&nbs

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(ii)  (a) Calculation of total number of carbon atoms
           Gram atomic mass of carbon (C-14) = 14 g = 14 × 10³ mg
            14 g or 14 × 10³ mg of carbon (C-14) has 6.022 × 10²³atoms

No of neutrons on 1 atom of (C-14) = 14-6= 8

⇒ No. of neutrons in 14g of (C-14) = 6.022× 10²³ ×8

So, 7 mg of carbon (C-14) has = (6.022 × 10²³ ×8) / (14 x 10³ mg) x (7 mg) = 2.408 × 10²¹ neutrons

        (b) Calculation of total number and total mass of neutrons
            Mass of one neutron = 1.675 × 10^-27 kg
            Mass of 2.408 × 10²¹ neutrons = (1.675 x 10^-27 kg) × 2.408 × 10²¹
= 4.033 × 10^-6 kg

(iii) (a) Calculation of total number of NH₃ molecules
Gram molecular mass of ammonia (NH₃) = 17 g = 17 × 10³ mg
17 × 10³ mg of NH₃ have molecules = 6.022 × 10²³

34 mg of NH₃ have molecules = (6.022 × 10²³) / (17 x 10³) x 34 mg = 1.2044 x 10²⁰ molecules

       (b) Calculation of total number and mass of protons
            No. of protons present in one molecule of NH₃ = 7 + 3 = 10
            No. of protons present in 12.044 × 10²⁰ molecules of NH₃ = 12.044 × 10²⁰ × 10
= 1.2044 × 10²² protons
            Mass of one proton = 1.67 × 10^-27 kg
            Mass of 1.2044 × 10²² protons = (1.67 × 10^-27 kg) × 1.2044 × 10²²
= 2.01 × 10^-5 kg

Since, the mass and number of protons is independent of the temperature and pressure conditions. So, there will no change in the answer upon changing the temperature and pressure because only the number of protons and mass of protons are involved.

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(i) One mole of methane (CH4) has = 6.022 × 1023 molecules      No. of electrons present in one molecule of CH4 = 6 + (4 x 1) = 10      No. of electrons present in 6.022 × 1023 molecules of CH4 = 6.022 × 1023 × 10      = 6.022 × 1024 electrons(ii)  (a) Calculation of total number of carbon atoms             Gram atomic mass of carbon (C-14) = 14 g = 14 × 103 mg             14 g or 14 × 103 mg of carbon (C-14) has 6.022 × 1023 atoms            No of neutrons on 1 atom of (C-14) = 14-6= 8            ⇒ No. of neutrons in 14g of (C-14) = 6.022× 1023 ×8            So, 7 mg of carbon (C-14) has = (6.022 × 1023 ×8) / (14 x 103 mg) x (7 mg) = 2.408 × 1021 neutrons         (b) Calculation of total number and total mass of neutrons               Mass of one neutron = 1.675 × 10-27 kg               Mass of 2.408 × 1021 neutrons = (1.675 x 10-27 kg) × 2.408 × 1021               = 4.033 × 10-6 kg (iii) (a) Calculation of total number of NH3 molecules             Gram molecular mass of ammonia (NH3) = 17 g = 17 × 103 mg             17 × 103 mg of NH3 have molecules = 6.022 × 1023            34 mg of NH3 have molecules = (6.022 × 1023) / (17 x 103) x 34 mg = 1.2044 x 1020 molecules        (b) Calculation of total number and mass of protons             No. of protons present in one molecule of NH3 = 7 + 3 = 10             No. of protons present in 12.044 × 1020 molecules of NH3 = 12.044 × 1020 × 10             = 1.2044 × 1022 protons             Mass of one proton = 1.67 × 10-27 kg             Mass of 1.2044 × 1022 protons = (1.67 × 10-27 kg) × 1.2044 × 1022             = 2.01 × 10-5 kgSince, the mass and number of protons is independent of the temperature and pressure conditions. So, there will no change in the answer upon changing the temperature and pressure because only the number of protons and mass of protons are involved.

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