Domain: Natural Science — Chemistry
Target concept: Homologs of benzene

Video generation prompt: At room temperature, a beaker contains an appropriate amount of dilute acidified potassium permanganate solution. An appropriate amount of toluene is added to the beaker, and the mixture is gently shaken.

Evaluation guide:
(i) Target concept: Toluene, a homolog of benzene, bears a reactive methyl (-CH₃) side chain on its aromatic ring that benzene itself lacks. When toluene is mixed with dilute acidified potassium permanganate solution at room temperature, this side chain is gradually oxidized by MnO₄⁻, consuming the permanganate and causing the solution's purple color to visibly fade, a reaction that benzene, having no oxidizable side chain, does not undergo.
Minimum mechanism: Toluene must first be added to the beaker and remain immiscible with the aqueous KMnO₄ solution, initially floating as a separate, colorless upper layer (toluene's density is below that of the aqueous solution); the beaker must then be swirled or shaken to bring the two layers into contact; following this mixing, the purple aqueous layer must visibly and gradually lose color across the sequence, while the toluene layer itself must remain colorless throughout.
(ii) Storyline: Frame 1–2: Static shot of the beaker holding the purple, acidified KMnO₄ solution, meniscus visible. Frame 3–5: A dropper enters from above, delivering colorless toluene toward the solution surface. Frame 6–7: Toluene droplets coalesce into a distinct, colorless upper layer above the purple solution. Frame 8–9: The beaker is gently swirled or shaken, visibly disturbing the flat interface between the two layers. Frame 10: The aqueous layer appears noticeably lighter in color than in Frame 1, while the toluene layer remains colorless and separate. Viewpoint is fixed frontal close-up; the beaker rim, both liquid layers, and their interface remain continuously visible with no occlusion.

Manual:
Experimental Procedure
1. Place a clean glass beaker on a lab bench.
2. Pour dilute acidified potassium permanganate solution (purple, aqueous) into the beaker until ~1/3 full.
3. Using a dropper, add 2–3 mL of toluene (colorless, immiscible) onto the surface of the solution.
4. Gently swirl or shake the beaker to bring the two layers into contact.
Observation of Experimental Phenomena
- Toluene initially floats as a separate colorless layer above the purple aqueous layer (lower density, immiscible).
- After shaking, the purple color of the aqueous layer gradually fades as the reaction proceeds.
- The toluene layer remains colorless throughout and does not turn purple.
- No gas evolution or significant heat is observed.
Summary of Experimental Principles
- Toluene is immiscible with the aqueous solution due to its nonpolar nature and lower density, so it initially forms a separate upper layer.
- Unlike benzene, toluene (a homolog of benzene) carries a reactive methyl side chain that can be oxidized by acidified potassium permanganate; this oxidation gradually consumes MnO₄⁻ ions, causing the characteristic purple color to fade.
- Benzene itself, lacking such a side chain, would not decolorize acidified KMnO₄ under the same conditions — illustrating a key chemical difference between benzene and its homologs.

Prompt Grounding rubric:
level_1: No beaker is shown; no purple potassium permanganate solution is visible; no toluene liquid appears; no addition or shaking action occurs; the scene does not resemble a room-temperature chemistry bench setup.
level_2: A container is present but is not a beaker (e.g., a flask, cup, or test tube); only one of the two required liquids (the potassium permanganate solution or the toluene) is visible, not both; toluene is never shown being added into the container; the purple solution and the added liquid are not visually distinguishable by color or transparency.
level_3: A beaker holding a purple aqueous solution (consistent with acidified potassium permanganate) is present; a separate colorless liquid (toluene) is visible in a dropper, pipette, or vial; toluene is shown being added into the beaker; however, toluene never actually reaches the solution surface (e.g., it stays suspended above the beaker or spills outside it).
level_4: The beaker containing the purple solution is present; colorless toluene is delivered onto the solution surface and forms a visible upper layer; the beaker is subsequently swirled or shaken, visibly disturbing the interface between the two liquids; both liquids remain individually identifiable throughout, with no object substitution, duplication, or unexplained deletion.
level_5: The beaker is clearly a cylindrical glass vessel with an open top and flat bottom; the purple acidified potassium permanganate solution occupies the lower portion with a visible meniscus; toluene is delivered from a calibrated dropper or pipette as discrete droplets that coalesce into a colorless upper layer; the beaker is then swirled or shaken so the two layers visibly meet at the interface without the toluene layer disappearing; both the beaker and both liquids remain continuously identifiable and correctly positioned relative to one another, toluene above and the aqueous layer below, from the first frame to the last.

Scientific and Causal Correctness rubric:
level_1: The purple color of the potassium permanganate solution remains completely unchanged in saturation and hue from the first frame to the last, even after toluene is added and the beaker is shaken; the toluene layer never separates from or visibly interacts with the aqueous layer in any way; nothing in the sequence suggests toluene and the acidified KMnO₄ solution are chemically distinct rather than simply inert liquids sitting together.
level_2: A change in the purple solution's appearance is shown, but it is scientifically inconsistent with side-chain oxidation: for example, the color fades completely and instantly the moment toluene touches the surface, before any mixing or shaking occurs, or the toluene layer itself takes on a purple tint, or the aqueous layer's color deepens rather than fades.
level_3: After toluene is added and the beaker is shaken, the purple aqueous layer visibly lightens in hue; the toluene layer stays colorless and remains visually separate above the aqueous layer; however, the timing of the fading does not correspond to the shaking action: for example, fading begins before the layers ever make contact, or all of the color loss happens in a single instantaneous jump rather than progressing across the sequence.
level_4: After toluene is added and the mixture is shaken, the purple aqueous layer's color progressively and visibly lightens across the remaining sequence, consistent with the methyl side chain of toluene being oxidized by the acidified permanganate; the toluene layer remains colorless and distinct throughout; the purple color never re-intensifies or reappears once it has faded.
level_5: The purple aqueous layer shows a clear, gradual lightening in hue that begins only once toluene has been added and the beaker shaken, not before contact, and not as a single instantaneous change; the toluene layer remains visibly colorless and separate from the aqueous layer at every frame, never adopting the purple hue; by the final frame the aqueous layer is noticeably paler than at the start, correctly showing that toluene, unlike benzene, reacts with and decolorizes acidified potassium permanganate through oxidation of its methyl group.

Spatiotemporal Consistency rubric:
level_1: The beaker's position on the bench changes abruptly between two frames with no motion connecting them, or the liquid level inside jumps without any corresponding pour or addition being shown; toluene appears already spread as a full upper layer with no dropper or delivery motion ever shown; the beaker's outline warps or breaks apart between frames; or the lighting shifts dramatically between frames (e.g., bright to dark with no transition).
level_2: The beaker stays roughly in place but tilts or rotates with no swirling or shaking motion shown to explain it; the boundary between the purple and colorless layers blinks in and out of view across frames; a toluene droplet appears at the solution surface with no visible path leading down from the dropper tip; the highlight on the beaker's glass surface jumps to a different spot or disappears even though neither the beaker nor the camera has moved.
level_3: The beaker stays upright in the same spot on the bench throughout; the toluene layer appears only after the dropper is shown moving down to the solution surface along a continuous, traceable path; once the beaker is swirled or shaken, its rotation is smooth and gradual rather than jumping between distinct angles; the reflection of the room's lighting on the glass shifts only in ways that match the beaker's own swirling motion.
level_4: The meniscus curvature changes smoothly and plausibly as the beaker is swirled, without flattening out or inverting; the boundary between the toluene and aqueous layers deforms gradually during swirling rather than snapping between distinct shapes from one frame to the next; the beaker rim and the liquid interface keep the same relative position to the bench and to each other throughout, with no sudden shift in camera perspective; the dropper's earlier delivery motion and the later swirling motion both read as continuous physical actions rather than being pieced together from mismatched moments.
level_5: The swirling motion of both liquid layers stays continuous from the moment shaking begins to when it ends, with each frame's liquid configuration reachable by smooth motion from the frame before it; the beaker's rim and the internal liquid interface can be tracked smoothly across the whole sequence with no snapping or skipped positions; the light reflection on the glass moves only in step with the beaker's own motion, the camera itself never shifts, and the toluene layer's color and position never revert to an earlier state once changed.