56. Radioactive tracers are useful in studying very low concentrations of chemical species. A
chemist has a sample of HgI2 in which part of the iodine is the radioactive nuclide of mass
131, so that the count rate is 5.0 1011 counts per minute per mole of I. The solid mercuric
iodide is placed in water and allowed to come to equilibrium. Then 100 mL of the solution
is withdrawn, and its radioactivity is measured and found to give 22 counts per minute.
What is the molar concentration of iodide ion in the solution?
57. Which statement is true about the following reaction?
Energy is absorbed in the reaction.
Energy is released in the reaction.
No energy change is associated with the reaction.
Not enough information is given to determine the energy change.
58. One of the hopes for solving the world’s energy problem is to make use of the fusion
reaction:
H + H → He + n + energy
How much energy is released when one mole of deuterium is fused with one mole of tritium
according to the above reaction? The masses of the atoms and the neutrons are:
H = 2.0140 amu H = 3.01605 amu
He = 4.002603 amu n = 1.008665 amu
The speed of light is 2.9979 108 m/s