Nuclear Chemistry — Practice · Grade 11 Science
Chapter: Redox, Cells & Nuclear ChemistryWhat this practice covers
By the end of Nuclear Chemistry you should be able to:
- I can describe alpha, beta, and gamma decay and write balanced nuclear equations for them.
- I can use half-life to calculate how much of a radioactive sample remains after a given time.
- I can compare nuclear fission and fusion as processes that convert mass into enormous amounts of energy.
9 questions, multiple choice, numeric and written answer, each with a worked explanation.
Vocabulary used: radioactivity, alpha decay, beta decay, gamma decay, half-life, nuclear fission, nuclear fusion.
Problem 1
- a high-energy photon
- a single proton
- a single electron
- a helium-4 nucleus (2 protons and 2 neutrons)
Answer and explanation
a helium-4 nucleus (2 protons and 2 neutrons)
An alpha particle is a helium-4 nucleus, ⁴₂He — two protons and two neutrons.
Problem 2
Answer and explanation
40 g
12 ÷ 6 = 2 half-lives, so the sample halves twice: 160 → 80 → 40 g (or 160 ÷ 2² = 40 g).
Problem 3
- increases by 1
- decreases by 1
- decreases by 2
- stays the same
Answer and explanation
increases by 1
In beta-minus decay, a neutron becomes a proton while an electron and antineutrino are emitted, so Z rises by 1 and A stays the same. Beta-plus decay follows a different change.
Problem 4
Answer and explanation
Fission splits a heavy nucleus into lighter ones — for example, uranium-235 splitting inside a nuclear power reactor. Fusion joins light nuclei into a heavier one — for example, hydrogen fusing into helium in the core of the Sun. Both release large amounts of energy.
Problem 5
Answer and explanation
1.5 g
6 ÷ 2 = 3 half-lives, so the sample halves three times: 12 → 6 → 3 → 1.5 g (or 12 ÷ 2³ = 1.5 g).
Problem 6
Hints
Balance both mass number and charge number.
Answer and explanation
A stays unchanged; Z increases by 1 as a neutron converts to a proton with emitted particles.
Problem 7
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
Dose, energy, exposure route, duration and shielding matter as well as radiation type.
Problem 8
Answer and explanation
No. Mass number is nucleon count; different binding energies can produce a rest-mass difference and energy transfer.
Fission splits a heavy nucleus into smaller products and can release neutrons; fusion combines light nuclei. Whether a specified channel releases energy depends on the complete initial/final mass and binding-energy account, not the claim that splitting or joining always releases energy. Mass-number sums count nucleons, while precise mass differences connect with E=Δmc². Use either nuclear or atomic masses consistently so electron masses are not accidentally omitted or double-counted. Reaction accessibility and control require a separate mechanism account.
No. Mass number is nucleon count; different binding energies can produce a rest-mass difference and energy transfer.
Response criteria
- Interpret labels, structures, axes, units and directions correctly.
- Explain the chemistry relationship or mechanism.
- Respect stated assumptions and distinguish observation from inference.
Problem 9
Answer and explanation
Daughter A=234 and Z=90, corresponding to thorium. Precise consistent masses or binding energies are needed for an energy calculation; mass-number conservation is not equality of exact rest masses.
Daughter A=234 and Z=90, corresponding to thorium. Precise consistent masses or binding energies are needed for an energy calculation; mass-number conservation is not equality of exact rest masses.
Response criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the chemical mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.