Question

Oxygen has three (3) naturally occurring isotopes of mass number 16, 17, and 18. The mass of oxygen-16 is 15.9949 amu and it occurs 99.75% of the time. The oxygen-17 isotope occurs 0.0370% of the time with a mass of 16.9993 amu, and the oxygen-18 isotope has a mass of 17.9992 amu with a 0.204% occurrence. Find the average atomic mass of oxygen.

Answer 1

The average atomic mass of oxygen, considering its isotopic composition and relative abundances, is calculated to be approximately 16.0424 amu.

Step-by-step explanation:

The average atomic mass of an element with multiple isotopes is calculated by multiplying the mass of each isotope by its relative abundance, and then adding these values together. For oxygen with its three isotopes (¹⁶O, ¹⁷O, and ¹⁸O), the calculation involves the following steps:

• Multiply the mass of each isotope by its percentage abundance (converted to decimal form).
• Add these products together to get the average atomic mass.

For oxygen:

• (15.9949 amu * 0.9975) + (16.9993 amu * 0.00037) + (17.9992 amu * 0.00204)
• ≈ (15.9994 amu) + (0.0063 amu) + (0.0367 amu)
• ≈ 15.9994 amu + 0.0063 amu + 0.0367 amu
• ≈ 16.0424 amu

Therefore, the average atomic mass of oxygen is 16.0424 amu.