A saturated Na₂CO₃ solution isprepared, and a small excess of solid ispresent (white pile in beaker). A seedcrystal of Na₂ ¹⁴CO₃(¹⁴C is a radioac-tive isotope of ¹²C) is added (small redpiece), and the radioactivity is mea-sured over time. (a) Would you expectradioactivity in the solution? Explain.(b) Would you expect radioactivity inall the solid or just in the seed crystal? Explain.
A saturated Na₂CO₃ solution isprepared, and a small excess of solid ispresent (white pile in beaker). A seedcrystal of Na₂ ¹⁴CO₃(¹⁴C is a radioac-tive isotope of ¹²C) is added (small redpiece), and the radioactivity is mea-sured over time. (a) Would you expectradioactivity in the solution? Explain.(b) Would you expect radioactivity inall the solid or just in the seed crystal? Explain.
SOLUTION:
Step 1:
(a). the initial solution has the following equilibrium:
Na2 12CO3 (s)↔ 2 Na+ (aq)+12CO32-(aq)
After the addition of the Na214CO3 seed crystal, the Na+ and 14CO32- ions in the solid Na214CO3 seed crystal are in dynamic equilibrium with the Na+ and 12CO32- ions in the solution:
Na214CO3 (s)↔2 Na+ (aq)+12CO32-(aq)
There will be a continuous exchange of material between the solid seed crystal and the solution. Some of the radioactive 14CO32- ions from the solid seed crystal will dissolve into the solution, while some of the non-radioactive 12CO32- ions from the solution will precipitate out into the solid state.
Thus, the radioactivity is expected from the dissolved radioactive 14CO32- ions.
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