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 is ` 7 mg of ^(14)C`.
( Assume that mass of neutron = ` 1.675 xx 10^(-27) kg)`.
(iii) find (a) the total number and (b) the total mas of protons in 34 mg of `NH_(3)` at STP .
will the answer change if the temperature and pressure are changed ?

Answer

(i) `24.096 xx 10^(20), (ii) 4.036 xx 10^(-7)kg`

Explanation

(i) `14g ""^(14)C` contains `6.023 xx 10^(23)` atoms,
Number of atoms in 7mg of `""^(14)C`
`=(6.023 xx 10^(23))/(14) xx (7)/(1000) =3.012 xx 10^(20)`
Mass number of `""^(14)C (A)=14`
Atomic number of `""^(14)C (Z)=6`
Number of neutrons in one atom of `""^(14)C=14-6=8`
Number of neutrons in 7mg of `""^(14)C=8 xx 3.012 xx 10^(20)`
`=24.096 xx 10^(20)`.
(ii) Mass of one neutron `=1.675 xx 10^(-27)kg`
Mass of neutrons present in `7"mg of "^(14)C`
`=24.096 xx 10^(20) xx 1.675 xx 10^(-27)=4.036 xx 10^(-6)Kg`