Question

The mass of a proton is 1.00728 amu and that of a neutron is 1.00867 amu. What is the mass defect (in amu) of a Ni nucleus? (The mass of a nickel- 60 nucleus is 59.9308 amu.)

Answer 1

Mass Defect: 0.5505 amu.

Explanation

A nickel-60 atom contains sixty nucleons (neutrons and protons).

• Nickel has atomic number 28 as seen on a periodic table. 28 out of the 60 nucleons are thus protons.
• The rest of the 60 - 28 = 32 nucleons are, therefore, neutrons.

According to the question,

• each proton has a mass of 1.00728 amu. 28 of them shall have a mass of $28 \times 1.00728  = 28.20384\; \text{amu}$;
• each neutron has a mass of 1.00867 amu. 32 of them shall have a mass of $32 \times 1.00867 = 32.27744 \; \text{amu}$.

Mass of the 60 nucleons shall add up to $28.20384 + 32.27744 = 60.48128 \; \text{amu}$.

The mass defect of a nucleus is "the difference between the sum of masses of [its] components and [its] measured [mass]." ("Map: A Molecular Approach (Tro)", Chemistry Libretexts)

According to the question, the measured mass of a nickel-60 nucleus is 59.9308 amu.

The difference between the sum of the masses of its nucleon components and the mass of its nucleus is, therefore, $60.48128 - 59.9308 = 0.5505\;\text{amu}$ (accurate to four decimal places.)