Question

Enter your answer in the provided box. The 235U isotope (atomic mass = 235.00) undergoes fission when bombarded with neutrons. However, its natural abundance is only 0.72 percent. To separate it from the more abundant 238U isotope (atomic mass = 238.00), uranium is first converted to UF, which is easily vaporized above room temperature. The mixture of 23SUF, and 238UF gases is then subjected to many stages of effusion. Calculate how much more quickly 235UF, effuses than 238UF. Give the answer as the ratio of rates of 235UF to 238UF to four decimal places.

Answer 1

The atomic mass of F is 19 g/mol

Molar mass of

235 U F6 = 235 + 6(19) = 349 g/mol

Molar mass of

238 U F6 = 238 +6(19) = 352 g/mol

The rate of effusion is inversely proportional to the square root of molar mass.

RM R =VM

R = rate of effusion of 235 U F6 R' = rate of effusion of 238 U FE M = molar mass of 235 U F6 M' = molar mass of 238 U F6

Substitute values in above equation

RM R =VM

R 352 R = V 349

R p = V1.008596

R = 1.0043