Question

A sample of carbon that contains 70% carbon-12 and 30% carbon-14. What do you think is the average atomic mass of this sample?

(a) 14.5

(b) 14.14

(c) 14

(d) 12

This question was addressed to me in class test.

This key question is from Atomic and Molecular Masses topic in division Chemistry Basic Concepts of Chemistry – Class 11

Answer 1

Correct option is (c) 14

For explanation I would say: Given that, carbon-12 is of 70% and carbon-14 is of 30%. In order to find avg atomic mass, you should add the products of multiplications 12 with 70/100 and 14 with 30/100. 12 x 0. 7 = 9.8; 14 x 0.3 = 4.2. Now adding them 9.8 + 4.2 = 14.