Question

The isotope chlorine-35 has a mass of 34.969 amu , and the isotope chlorine-37 has a mass of 36.966 amu .  Given that 75.5 % of all chlorine atoms found in nature are chlorine-35 and 24.5 % are chlorine-37, find the atomic mass of chlorine, Cl(atomic number 17).

Answer 1

Average atomic mass is given by:

Avg mass = M_avg = (Amount of Cl-35*weight of Cl-35 + Amount of Cl-37*weight of Cl-37)/(total amount of Cl-35 and Cl-37 in nature)

Amount of Cl-35 in nature = 75.5% = 0.755

Amount of Cl-37 in nature = 24.5% = 0.245

Weight of Cl-35 = 34.969 amu

Weight of Cl-37 = 36.966 amu

Using above values:

M_avg = (0.755*34.969 + 0.245*36.966)/(0.755 + 0.245)

M_avg = 35.458 amu = atmoic mass of chlorine

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