(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.
Answers
Explanation:
Total number of electrons present in 1 methane molecule =6+4=10.
Total number of electrons resent in 1 mole of methane =10×6.023×10
23
=6.023×10
24
electrons.
The number of neutrons is equal to the difference in the mass number and atomic number.
It is equal to $$\d
isplaystyle 14-6=8 $$.
(ii)(a) The number of neutrons present in 7 mg of C-14 is
14
6.023×10
23
×8
×7×10
10−3
=2.4088×10
21
neutrons.
(b) Total mass of neutrons in 7 mg of C-14 is 2.4088×10
21
×1.675×10
−27
4.035×10
−6
kg.
(iii)(a)Number of protons present in 1 molecule of ammonia =7+3=10.
Number of molecules present in 34 mg of ammonia is
17
6.023×10
23
×34×10
−3
=1.2044×10
21
.
Total number of protons present in 34 mg of ammonia=10×1.2044×10
21
=1.2044×10
22
(b) Total mass of protons present in 34 mg of ammonia at STP is 1.6726×10
−27
×1.204×10
22
=2.0138×10
−5
kg.
When temperature and pressure are changed, there is no difference in the answer.