A sample of oxygen contains two isotopes of oxygen with masses 16 u and 18 u respectively. The proportion of these isotopes in the sample is 3 : 1. What will be the average atomic mass of oxygen in this sample?

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Q: 13 (NDA-II/2018)
A sample of oxygen contains two isotopes of oxygen with masses 16 u and 18 u respectively. The proportion of these isotopes in the sample is 3 :
1. What will be the average atomic mass of oxygen in this sample?

question_subject: 

Science

question_exam: 

NDA-II

stats: 

0,10,25,8,6,11,10

keywords: 

{'average atomic mass': [0, 0, 0, 1], 'isotopes': [0, 0, 3, 6], 'oxygen': [3, 0, 1, 0], 'proportion': [1, 1, 2, 8], 'sample': [0, 0, 3, 5], 'masses': [1, 1, 0, 7]}

The correct answer is option 4, 16.5 u. The average atomic mass of an element is calculated by taking into account the mass and proportion of each isotope present in a sample. In this case, the sample contains two isotopes of oxygen with masses of 16 u and 18 u, and the proportion of these isotopes is given as 3:1.

To calculate the average atomic mass, we use the formula:

Average atomic mass = (mass of first isotope * proportion of first isotope) + (mass of second isotope * proportion of second isotope)

Using the given proportions, we have:

Average atomic mass = (16 u * 3) + (18 u * 1) = 48 u + 18 u = 66 u

Finally, to find the average atomic mass per oxygen atom, we divide by the total number of isotopes in the sample, which is 4 (3 + 1):

Average atomic mass = 66 u / 4 = 16.5 u

Therefore, the average atomic mass of oxygen in this sample is 16.5 u.