Question

Thallium-201 is a radioactive isotope that undergoes first-order decay. When the concentration of 201Tl is 0.0042 M, its half-life is 73.0 hours. What is the half-life of 201Tl when its concentration is 0.0136 M?

(A) 51.0 hours

(B) 73.0 hours

(C) 123 hours

(D) 236 hours

Answer 1

Answer:

(B) 73.0 hours.

Explanation:

• It is known that the decay of a radioactive isotope isotope obeys first order kinetics.

• Half-life time is the time needed for the reactants to be in its half concentration.

• If reactant has initial concentration [A₀], after half-life time its concentration will be ([A₀]/2).

• Also, it is clear that in first order decay the half-life time is independent of the initial concentration.

So, the half-life of 201Tl when its concentration is 0.0136 M is (B) 73.0 hours.