(ii) One mole ofelectrons = 6.022 × 10²³ electrons
Mass of 1 electron = 9.1 × 10^-31 kg
Mass of 6.022 × 10²³ electrons = (9.1 × 10.31kg) × (6.022 × 10²³)= 5.48 × 10^-7 kg
Charge on one electron = 1.602 × 10^-19 coulomb
Charge on one mole electrons = 1.602 × 10^-19 × 6.022 × 10²³ =9.65 × 10⁴ coulombs

Question - 2 : - (i) Calculate the total number of electronspresent 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 ofa 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 thetemperature and pressure are changed ?

Answer - 2 : -

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

(ii) Step I. Calculation of totalnumber of carbon atoms
Gram atomic mass of carbon (C-14) = 14 g = 14 × 10³ mg
14 × 10³ mg of carbon (C-14) have atoms = 6.022 × 10²³

Step II. Calculation oftotal number and tatal mass of neutrons
No. of neutrons present in one atom (C-14) of carbon = 14 – 6 = 8
No. of neutrons present in 3-011 × 10²⁰ atoms (C-14) of carbon= 3.011 × 10²⁰ × 8
= 2.408 × 10²¹ neutrons
Mass of one neutron = 1.675 × 10^-27 kg
Mass of 2.408 × 10²¹ neutrons = (1.675X10^-27 kg)× 2.408 × 10²¹
= 4.033 × 10^-6 kg.

(iii)Step I. Calculation of totalnumber ofNH₃ molecules
Gram molecular mass of ammonia (NH₃) = 17 g = 17 × 10³ mg
17 × 10³ mg of NH₃ have molecules = 6.022 × 10²³

Step II. Calculation oftotal 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.
No, the answer will not change upon changing the temperature and pressurebecause only the number of protons and mass of protons are involved.

Question - 3 : - How many protons and neutrons are present inthe following nuclei

Answer - 3 : -

Question - 4 : - Write the complete symbol for the atom (X)with the given atomic number (Z) and atomic mass (A)
(i) Z = 17,A = 35
(ii) Z = 92, A = 233
(in) Z = 4, A = 9.

Answer - 4 : -

Question - 5 : - Yellow light emitted from a sodium lamp has awavelength (2) of 580 nm. Calculate the frequency (v) and wave number (v) ofyellow light.

Answer - 5 : -

Question - 6 : - Calculate the energy of each of the photonswhich
(i) correspond to light of frequency 3× 1015 Hz
(ii) have wavelength of 0-50 A.

Answer - 6 : - (i) Energy of photon (E) = hv
h = 6.626 × 10^-34 J s ; v = 3 × 10¹⁵ Hz = 3 ×10¹⁵s^-1
∴ E = (6.626 × 10^-34 Js) × (3 × 10¹⁵ s^-1) = 1.986 × 10¹⁸ J
Energy of photon (E) = hv = hcλ
h = 6.626 × 10 34 J s; c = 3 × 10⁸ m s^-1 ;
λ= 0.50 Å = 0.5 × 10^-10 m.

Question - 7 : - Calculate the wavelength, frequency, andwavenumber of lightwave whose period is 2.0 × 10^-10 s.

Answer - 7 : -

Question - 8 : - What is the number of photons of light withwavelength 4000 pm which provide 1 Joule of energy ?

Answer - 8 : - Energy of photon (E) = hcλ
h = 6.626 × 10^-34 Js, c = 3 × 10⁸ m s^-1,λ = 4000 pm = 4000 × 10^-12 = 4 × 10^-9 m

Question - 9 : - A photon of wavelength 4 × 10^-7 mstrikes on metal surface ; the work function of the metal being 2.13 eV.Calculate (i) the energy of the photon,
(ii) the kinetic energy of the emission
(iii) the velocity of thephotoelectron. (Given 1 eV = 1.6020 × 10^-19 J).

Answer - 9 : -

Question - 10 : - Electromagnetic radiation of wavelength 242 nmis just sufficient to ionise the sodium atom. Calculate the ionisation energyof sodium in k-J mol^-1.

Answer - 10 : -

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