Question

Can somebody walk me through this question?

The mass of a proton is 1.00728 atomic mass units (amu) and the mass of a neutron is 1.00867 amu. What is the mass defect (in amu) of a nucleus whose nuclear mass is 59.9338 amu? What is the mass defect in kilograms? What is the energy equivalent of this mass in kilojoules?

So far, I think I've gotten the mass defect in amu, so check my work please? And help me with converting it to kg and kj?

So for amu I multiplied the protons & neutrons atomic mass and subtracted 60.48247 - 59.9338 to get 0.54867 amu. Is that right?

Answer 1

Well, it would have helped if you mentioned how many neutrons and protons there were in that nucleus so I searched for an isotopic mass of 59.9338 atomic mass units and finally found cobalt (60) which has a nuclear mass of 59.9338171 amu and has 27 protons and 33 neutrons.

27 protons have a mass of (27*1.00728) = 27.19656 amu
33 neutrons have a mass of (33*1.00867) = 33.28611 amu
totaling 60.48267 amu which agrees with your calculation to 3 decimal places

Calculating the mass defect we get:
60.48267 amu
-59.9338171 amu which equals
0.5488529 amu
which again agrees with your calculations to 3 decimal places.
This converts to 9.1139 x 10^-28 kilograms

Converting this mass to energy by the famous E=mc² equation we get
8.1912e-11 joules
A good calculator for mass to energy equivalence can be found here:
http://www.1728.org/einstein.htm

(I hope this helps you a little)

Answer 2

It did wow, thank you so much!

Answer 3

Glad I could help you out.
(Once I did that search for an isotope with a nuclear mass of 59.9338171 atomic mass units and found cobalt (60), I knew this problem had me hooked.)