 Given that natural sample of iron has isotopes in the ratio 5%, 90% and 5% respectively. What will be the average atomic mass of Fe? Write any two applications of isotopes.

 The relative atomic mass of boron is 10.8. Calculate the percentage of its isotopes occurring in nature.
 Write the number of neutrons present in C and C isotopes of carbon.
Write the number of neutrons present in C and C isotopes of carbon
 Average atomic mass of Fe = = = = 55.95 u
Two applications of isotopes are C14 is used to determine the age of old samples of fossils.
 Co60 is used in the treatment of cancer (radiotherpy).

 Let the percentage of be Y in the sample and the percentage of will be (100  Y) .
Average mass =
10Y + 11(100  Y) = 1.08 x 100
10Y + 1100  11Y = 108
⇒ Y = 20
Therefore, the percentage of = 20% and percentage of = 100  20 = 80%.  Number of neutron in = Mass number  atomic number = 12  6
Number of neutrons in = 14  6 = 8
 Let the percentage of be Y in the sample and the percentage of will be (100  Y) .