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 ?



Q.2:- (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 ?

 

Answer:-

(i) Electrons present in 1 molecule of methane (CH4) = 6+4 = 10

∴ Electrons in  mol i.e. 6.022×1023 molecules = 6.022×1024

(ii) (a) Number of atoms in 14C in 1 mole= 6.022×1023 atoms
1 atom of 14C contains = 14-6 = 8 neutrons.



∴ The number of neutrons in 14 g of 14C = 6.022×1023×8 neutrons
Number of neutrons in 7 mg = (6.022×1023×8×7)/14000 = 2.4088×1021 neutrons
(b) Mass of one neutron = 1.674×10-27kg
Mass of total neutrons in 7 g of 14C = (2.4088×1021) (1.675 ×10-27 kg) = 4.035 ×10-6 kg
(iii) (a) 1 mol of NH= 17g NH= 6.022×1023 molecules of NH
1 atom of NH3  contains = 7+3 = 10 protons
∴ The number of protons in 1 mol of NH= 6.022×1024 protons.
Number of protons in 34 mg of NH= (6.022×1024×34)/17×1000 = 1.2044×1022 protons.
(b) Mass of one proton = 1.6726×10-27kg
∴ Mass of 1.2044×1022 protons = (1.6726×10-27) ×(1.2044×1022) kg = 2.0145×10-5 kg.
No, there will be no effect of temperature and pressure.