به انگلیسی

One electron, two ways to push it

Science · Chemistry · ages 23-24

Name ______________________ Date ____________

In electron transfer, what are the donor and acceptor called, in that order?
- Proton donor and proton acceptor
- Dissolved solute and bulk solvent
- Reductant and oxidant
A species loses an electron in a reaction. What happened to it?
- It was oxidized
- It was reduced
- It stayed unchanged
Anodic oxidation can replace a consumed chemical oxidant, but the full cell still needs a cathodic reaction.
Circle one: True False
For PC* donating to A, Ered(A/A-) = -0.90 V and Ered(PC+/PC*) = -0.60 V on the same reference scale. Neglect other energetic terms. How is this transfer classified?
- Thermodynamically unfavoured
- Thermodynamically favoured
- Exactly at equilibrium in this model
PC* donates an electron to a substrate. A later step restores PC. What is the quenching cycle called?
- Reductive quenching
- Oxidative quenching
- Ground-state excitation
Combine D+ -> D2+ + e- and A + e- -> A-. Which net equation follows after cancelling electrons?
- D+ + A -> D + A+
- D+ + A -> D2+ + A-
- D+ + A -> D2+ + A+ + 2e-
A positive calculated delta E proves that excited-state electron transfer will be fast and that the catalyst will complete a productive cycle.
Circle one: True False
Radical coupling competes with trapping by substrate. Substrate concentration is held fixed. Which change can favour trapping by lowering radical concentration?
- Raise the radical generation rate
- Remove the radical-trapping substrate
- Lower the radical generation rate

Answer key

For grown-ups. Fold this page away before handing over the rest.

Reductant and oxidant · The donor reduces its partner and is the reductant. The acceptor oxidises its partner and is the oxidant.
It was oxidized · Losing electrons is oxidation; gaining them is reduction.
True · The anode removes electrons. A paired cathodic reaction accepts electrons elsewhere in the cell.
Thermodynamically unfavoured · Delta E = -0.90 - (-0.60) = -0.30 V. This negative value makes transfer unfavourable in the stated model.
Oxidative quenching · PC* is oxidised when it loses an electron, so this is oxidative quenching.
D+ + A -> D2+ + A- · One electron is produced and one consumed. Cancelling them gives D+ + A -> D2+ + A-, with total charge +1 on each side.
False · Positive delta E supports favourable thermodynamics in the model. Transfer kinetics, excited-state decay and catalyst regeneration need separate assessment.
Lower the radical generation rate · Coupling depends on radical concentration squared. Slower generation can lower radical concentration while substrate remains available.