Question

Find (a) the total number neutron and (b) the total mass of neutrons in 7 mg of ${}^{14}C$.

[Assume that mass of a neutron =$1.675\times {10}^{-27}kg$]

Answer 1

The number of neutrons is equal to the difference in the mass number and atomic number.

It is equal to $14-6=8$.

(a) The number of neutrons present in 7 mg $(7\times {10}^{-3}g)$ of C-14:

$=\frac{7\times {10}^{-3}}{14}\times 6.02\times {10}^{23}\times 8$

$=2.408\times {10}^{21}$ neutrons

(b) Total mass of neutrons in 7 mg of C-14: ( mass of one neutron $=1.675\times {10}^{27}kg$

$=2.4088\times {10}^{21}\times 1.675\times {10}^{-27}$

$=4.035\times {10}^{-6}kg$.