Question

Enter your answer in the provided box. Alpha particles produced by radioactive decay eventually pick up electrons from their surroundings to form helium atoms. Calculate the volume (in mL) of He collected at STP when 2.30 g of pure 226Ra is stored in a closed container for 136 years. (Assume that there are five alpha particles generated per 226Ra as it decays to 206Pb.)

Answer 1

Number of moles of 226Ra = 2.3/226.025 = 0.01017 moles

number of 226Ra atoms = 0.01017 * 6.023 * 10^23 atoms

                      = 6.1254 * 10^21 atoms

1 atom of 226Ra produces 5 atoms of He

6.1254 * 10^21 atoms of 226 Ra produces 5 * 6.1254*10^21 atoms of He

                                       = 3.0627 * 10^22 atoms of He

Number of moles of He = 3.0627 * 10^22/(6.023 * 10^23)

                      = 0.05085 moles

PV = nRT

1 * V = 0.05085 * 0.0821 * 273

V = 1.1397 L of He is produced

Volume of He gas = 1.1397 * 10^3 mL = 1139.7 mL