Question

A sample of Rh-105 (104.906 g/mol) has an activity of 4.89 x 1021 Bq. What mass of Rh-105 is lost after 7 minutes?

Calculate the answer ____________ g Rh-105 is lost.

Answer 1

Activity of sample = 4.89 x 10²¹ Bq

Activity of sample = 4.89 x 10²¹ Bq * (1 disintegrations per second (dps) / 1 Bq)

Activity of sample = 4.89 x 10²¹ dps

Time = 7 min

Time = 7 * (60 s / 1 min)

Time = 420 s

Total disintegrations = (Activity of sample) * (Time)

Total disintegrations = (4.89 x 10²¹ dps) * (420 s)

Total disintegrations = 2.05 x 10²⁴ disintegrations

Total atoms lost = Total disintegrations

Total atoms lost = 2.05 x 10²⁴ atoms

moles of Rh-105 lost = (Total atoms lost) / (Avogadro's number)

moles of Rh-105 lost = (2.05 x 10²⁴ atoms) / (6.022 x 10²³ atoms/mol)

moles of Rh-105 lost = 3.41 mol

mass of Rh-105 lost = (moles of Rh-105 lost) * (molar mass Rh-105)

mass of Rh-105 lost = (3.41 mol) * (104.906 g/mol)

mass of Rh-105 lost = 357.8 g