A rock contains 2.28 g of U-235 and 6.79 g of Pb-207. Assume that when the rock formed it contained no Pb-207 and that a
Posted: Fri May 06, 2022 11:38 am
A rock contains 2.28 g of U-235 and 6.79 g of Pb-207.
Assume that when the rock formed it contained no Pb-207 and that
all Pb-207 that formed in the rock due to decay of the U-235 is
still there. (Neither of these assumptions is necessarily, or even
likely, to be true.) The half-life U-235
is 7.04 × 108 years.
For these calculations use the approximation that the
atomic weight is equal to the mass number. For example, the atomic
weight of U-235 is 235 g/mol.
(a) How many U-235 nuclei are in the rock now?
(b) How many Pb-207 nuclei are in the rock now?
(c) How many U-235 nuclei were in the rock when it formed? (d) How
old is the rock?
Assume that when the rock formed it contained no Pb-207 and that
all Pb-207 that formed in the rock due to decay of the U-235 is
still there. (Neither of these assumptions is necessarily, or even
likely, to be true.) The half-life U-235
is 7.04 × 108 years.
For these calculations use the approximation that the
atomic weight is equal to the mass number. For example, the atomic
weight of U-235 is 235 g/mol.
(a) How many U-235 nuclei are in the rock now?
(b) How many Pb-207 nuclei are in the rock now?
(c) How many U-235 nuclei were in the rock when it formed? (d) How
old is the rock?