Question

The mass defect for a Li-6 nucleus is -0.03434 g/mol. How do you calculate the atomic mass of Li-6?

Answer 1

6.04783 a.m.u

Explanation:

`Li-6" "`nucleus has 3 protons and 3 neutrons.

The total mass of protons in the nucleus

`= 3xx1.0072766 \ a.m.u.\= 3.02183 \ a.m.u`

The total mass of neutrons in the nucleus

`= 3xx1.0086654 \ a.m.u. = 3.02600 \ a.m.u`

The mass defect `= 0.03434 \ g/(mol)`

`= 0.03434 \ g/(mol.) xx (6.02xx10^23 \ " a.m.u")/g xx (1\ mol.)/(6.02xx10^23 \ "atom"`

`= 0.03434 \ color(red) cancel (g)/(color(green)cancel(mol.)) xx (6.02xx10^23 \ "a.m.u")/color(red) cancel(g)xx (1\ color(green)cancel(mol.))/(6.02xx10^23 \ "atom"`

`=03434 \ (a.m.u)/("atom")`

Total mass of the nucleons ( protons + neutrons)

`= 6.04783 \ a.m.u`

Mass of the nucleus

`= "Total mass of the nucleons" - "mass defect"`

`= 6.04783 \ a.m.u - 03434 \ a.m.u`

`= 6.04783 \ a.m.u`

Note that the mass defect is due to the binding energy - i.e. The energy required to keep the nucleons together in the nucleus.