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Class 11
Chemistry
Structure of Atom
i calculate the total number of electrons presen...

Question:
(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^–27 kg).

(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 chang

Answer:

(i) Molecule of CH⁴ (methane) contains electron = 10
Therefore 1 mole (6.022 x 10²³ atoms) contains electron = 6.022 x 10²⁴

(ii) a) 1g atom of 14C = 14g = 6.022 x 10²³ atoms = 6.022 x 10²⁴ x 8 neutrons
Thus 14g or 14000 mg have 6.022 x 10²⁴ x 8 neutrons
Therefore 7 mg will have neutrons = 6.022 x 10²⁴ x 8 / 14000 x 7 = 2.4088 x 10²²

b) mass of 1 neutron = 1.675 x 10^-27kg
Therefore mass of 2.4088 x 10²¹ neutrons = 2.4088 x 10²¹ x 1.67 x 10^-27 = 4.0347 x 10^-6 kg

(iii) a) 1 mol of NH₃ = 17g NH₃ = 6.022 x 10²³ molecules of NH₃ = (6.022x10²³)(7 + 3) proton = 6.022 x 10²⁴ protons
Therefore 34 mg i.e 0.034 g NH₃ = 6.022 x 10²⁴ x 0.034/1 = 1.2044 x 10²²protons

b) mass of 1 proton = 1.6726 x 10^-27 kg
Therefore mass of 1.2044 x 10²² protons = (1.6726 x 10^-27)(1.2044 x 10²²) kg = 2.0145 x 10^-5 kg

No, the answer will not change with change in temperature & pressure.

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