Calculate Binding Energy...?

Question

Question:

An atom of 49K has a mass of 48.965514 amu. Calculate the binding energy in MeV per NUCLEON. Use the masses:

mass of 1H atom = 1.007825 amu
mass of a neutron = 1.008665 amu
1 amu = 931.5 MeV

Correct answer: 8.424
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ok, so this is what I tried:

1) Find mass defect, (19x1.007825)+(30x1.008665) - 48.965514 = .443111amu
2) Multiply that by 931.5 MeV...

As you can see, I'm not really sure what I'm doing. I'd appreciate any help, thanks!

Answer 1

Well, I'm not sure where you got the 19 and 30, but I'm guessing you estimated the number of protons and neutrons. It's a reasonable guess, but it is a Titanium atom with 22 protons and 27 neutrons. So you take 22*1.007825 + 27*1.008665 - 48.965514 = .440591. Then you divide by 49 beacuse it asks for binding energy per nucleon, and then you can convert to MeV. So you do .440591/49*931.5=8.3757... MeV.