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 ?

Explanation

(i) Number of electrons in one molecular of `CH_4`
`=6+(1 xx 4)=10`
One mole of methane would contain `6.022 xx 10^(23)` molecules. Hence, total number of elecgrons in one mole of methane
`=10 xx 6.022 xx 10^(23)=6.022 xx 10^(24)`
(ii) (a) One mole of `""^(14)C` (14 g) contains `6.022 xx 10^(23)` atoms.
Number of `""^(14)C` atoms present in 7mg (0.007 g) of `""^(14)C`
`=(6.022 xx 10^(23))/(14) xx 0.007 =3.01 xx 10^(20)`
One atom of `""^(14)C` contains 8 neutrons.
Number of neutrons present in 7 mg of `""^(14)C`
`=3.01 xx 10^(20) xx 8`
`=2.4088 xx 10^(21)`
(b) Mass of neutrons present in 7 mg of `""^(14)C`
`=2.4088 xx 10^(21) xx 1.675 xx 10^(-27)`
(iii) (a) Number of protons in one molecule of `NH_3`
`=7+(1 xx 3) =10`
At S.T.P., one mole of ammonia (17 g) contains `6.022 xx 10^(23)` molecules.
Number of molecules present in 34 mg (= 0.034 g) of ammonia `=(6.022 xx 10^(23))/(17) xx 0.034=1.2044 xx 10^(21)`
Hence, number of protons in 34 mg of ammonia
`=1.2044 xx 10^(21)xx 10 = 1.2044 xx 10^(22)`
(b) Total mass of protons in 34 mg of ammonia
`=1.2044 xx 10^(22) xx 1.67262 xx 10^(-27)`
`=2.0145 xx 10^(-5)kg`
`("Mass of a proton "= 1.67262 xx 10^(-27)kg)`
There is no effect of temperature and pressure on the calculated values