Question

(a) The average atomic mass of a sample of an element X is 35.5u. What are the percentages of isotopes ₁₇X³⁷ and ₁₇X³⁵ in the sample ? 

(b) Write any two applications of isotopes. 

Answer 1

(a) Let the percentage of ₁₇X ³⁷ is p 

Percentage of ₁₇X ³⁵ = (100 – p) 

Average atomic weight = 35.5 

Therefore 

35.5 = 37p + 35(100 − p) /100 

3550 = 37p + 3500 − 35p 

3550 – 3500 = 37p - 35p 

2p = 50 ⇒ p = 25% 

Therefore, sample of ₁₇X ³⁷ is 25% and ₁₇X ³⁵ will be 100 – 25 = 75% 

(b) Cesium 137 – Used to treat cancerous tumors. Calcium 47 – It is an important aid for biomedical researchers studying the cellular functions