Plutonium-236 is an alpha emitter with a half-life of 2.86 years. If a sample initially contains 1.35 mg of Pu-236, what mass of Pu-236 is present after 5.00 years?

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SORT You are given the initial mass of Pu-236 in a sample and asked to find the mass after 5.00 years. STRATEGIZE Use the integrated rate law (Equation 21.3) to solve this problem. You must determine the value of the rate constant (k) from the half-life expression (Equation 21.1). Use the value of the rate constant, the initial mass of Pu-236, and the time along with integrated rate law to find the final mass of Pu-236. Since the mass of the Pu-236 (mpu-236) is directly proportional to the number of atoms (N), and since the integrat- ed rate law contains the ratio (N₁/No), you can substitute the initial and final masses for the initial and final number of atoms. GIVEN: Mpu-236(initial) = 1.35 mg; t = 5.00 yr; t1/2 = 2.86 yr FIND: Mpu-236(final) CONCEPTUAL PLAN [1/2 ty2 = 0.693 k k k, mpu-236(initial), t N₁ In No -kt mpu-236(final)