Answer:
63.55 amu
Explanation:
The average atomic mass of an element can be calculated by multiplying the decimal abundance of each isotope of that element by the relative atomic mass and summing them up. That is;
Average atomic mass = {atomic mass of isotope 1 × decimal abundance of Isotope 1} + {atomic mass of isotope 2 × decimal abundance of isotope 2}
According to this question, two most abundant isotopes of copper contain 34 and 36 neutrons. The atomic mass of each isotope can be found by adding the no. of neutrons to the atomic number/proton no., which is 29.
Atomic mass of Isotope 1= 34 + 29 = 63
Atomic mass of Isotope 2= 36 + 29 =65
Decimal abundance of each isotope = percentage abundance ÷ 100
Isotope 1 (with 34 neutrons) = 72.5% = 72.5/100 = 0.725
Isotope 2 (with 36 neutrons) = 100 - 72.5 = 27.5% = 27.5/100 = 0.275
Therefore, the average atomic mass
= {63 × 0.725} + {65 × 0.275}
= {45.675} + {17.875}
= 63.55
Hence, the average atomic mass of copper is 63.55 amu
