# 12.E: Nuclear Chemistry (Exercises)

1. Given that many elements are metals, suggest why it would be unsafe to have radioactive materials in contact with acids.

2. Many alpha-emitting radioactive substances are relatively safe to handle, but inhaling radioactive dust can be very dangerous. Why?

3. Uranium can be separated from its daughter isotope thorium by dissolving a sample in acid and adding sodium iodide, which precipitates thorium(III) iodide:

Th3+(aq) + 3I(aq) → ThI3(s)

If 0.567 g of Th3+ were dissolved in solution, how many milliliters of 0.500 M NaI(aq) would have to be added to precipitate all the thorium?

4. Thorium oxide can be dissolved in an acidic solution:

ThO2(s) + 4H+ → Th4+(aq) + 2H2O(ℓ)

How many milliliters of 1.55 M HCl(aq) are needed to dissolve 10.65 g of ThO2?

5. Radioactive strontium is dangerous because it can chemically replace calcium in the human body. The bones are particularly susceptible to radiation damage. Write the nuclear equation for the beta emission of strontium-90.

6. Write the nuclear equation for the beta emission of iodine-131, the isotope used to diagnose and treat thyroid problems.

7. A common uranium compound is uranyl nitrate hexahydrate [UO2(NO3)2_6H2O]. What is the formula mass of this compound?

8. Plutonium forms three oxides: PuO, PuO2, and Pu2O3. What are the formula masses of these three compounds?

9. A banana contains 600 mg of potassium, 0.0117% of which is radioactive potassium-40. If 1 g of potassium-40 has an activity of 2.626 × 105 Bq, what is the activity of a banana?

10. Smoke detectors typically contain about 0.25 mg of americium-241 as part of the smoke detection mechanism. If the activity of 1 g of americium-241 is 1.26 × 1011 Bq, what is the activity of americium-241 in the smoke detector?

11. Uranium hexafluoride (UF6) reacts with water to make uranyl fluoride (UO2F2) and hydrogen fluoride (HF). Balance the following chemical equation:

UF6 + H2O → UO2F2 + HF

12. The cyclopentadienyl anion (C5H5) is an organic ion that can make ionic compounds with positive ions of radioactive elements, such as Np3+. Balance the following chemical equation:

NpCl3 + Be(C5H5)2 → Np(C5H5)3 + BeCl2

1. Acids can dissolve metals, making aqueous solutions.

2. Alpha rays are dangerous only when the alpha emitter is in direct contact with tissue cells inside the body.
1. 14.7 mL

4. 104 mL
1. $$\mathrm{^{90}_{38}Sr\rightarrow \, _{-1}^{0}e + \, _{39}^{90}Y}$$
6. $$\mathrm{^{131}_{53}I\rightarrow \, _{-1}^{0}e + \, _{54}^{131}Xe}$$
1. 502 g/mol

8. PuO = 260.06 g/mol; PuO2 = 276.06 g/mol; Pu2O3 = 536.12 g/mol

10. 3.15 x 107 Bq

11. UF6 + 2H2O → UO2F2 + 4HF

12. 2NpCl3 + 3Be(C5H5)2 → 2Np(C5H5)3 + 3BeCl2

1. Radioactivity is the spontaneous emission of particles and radiation from atomic nuclei.

2. C-14 or 14C is an example of radioactive isotope (answers may vary).
1. 5 protons; 6 neutrons
2. 13 protons; 14 neutrons
3. 26 protons; 30 neutrons
4. 86 protons; 138 neutrons
4.
1. 1 proton; 1 neutron
2. 48 protons; 64 neutrons
3. 99 protons;153 neutrons
4. 19 protons; 21 neutrons
1. An alpha particle is a combination of two protons and two neutrons and is equivalent to a helium nucleus.

6. A beta particle is an electron.
1. Gamma rays are high-energy electromagnetic radiation given off in radioactive decay.

8. Gamma rays have no mass. Hence not a particle.
1. $$\mathrm{^{244}_{94}Pu\rightarrow \, _2^4He +\, ^{240}_{92}U}$$; the daughter isotope is $$\mathrm{^{240}_{92}U}$$, an atom of uranium.

10. $$\mathrm{^{212}_{87}Fr\rightarrow \, _2^4He +\, ^{208}_{85}At}$$; the daughter isotope is $$\mathrm{^{208}_{85}At}$$, an atom of astatine.

11. $$\mathrm{_{50}^{121}Sn \rightarrow \, _{-1}^0e + \, _{51}^{121}Sb}$$; the daughter isotope is $$\mathrm{_{51}^{121}Sb}$$, an atom of antimony.

12. $$\mathrm{_{43}^{99}Tc \rightarrow \, _{-1}^0e + \, _{44}^{99}Mo}$$; the daughter isotope is $$\mathrm{_{44}^{99}Mo}$$, an atom of antimony.

13. 0.512 MeV

14. 3.16 x 10-14 J

15. Beta particles; shielding of the appropriate thickness can protect against both alpha and beta particles.

16. Gamma rays; can be shielded by thick, dense material such as lead (Pb). Alpha particles has low energy; can shielded by a piece of paper.

17. Nuclear fission is when large nuclei break down into smaller nuclei.

18. A nucleus must be very large. Examples are Th-232 and U-235.