Domain: Engineering — Civil & Environmental Engineering
Target concept: Electrolytic Chromium-Containing Wastewater

Video generation prompt: Yellow wastewater containing hexavalent chromium (Cr⁶⁺) was introduced into a transparent electrolysis cell. The anode (iron electrode) was connected to the positive terminal of a direct current power supply, while the cathode (graphite electrode) was connected to the negative terminal. The electrodes were fully immersed in the wastewater and maintained a fixed distance apart. A stable direct current was then applied after closing the circuit.

Evaluation guide:
(i) Target concept: Electrochemical reduction of Cr⁶⁺ to Cr³⁺ in wastewater using sacrificial iron anode and inert graphite cathode.
Minimum mechanism: The iron anode must oxidize (Fe⁰ → Fe²⁺) once the circuit is closed, releasing Fe²⁺ into solution; this Fe²⁺ then chemically reduces Cr⁶⁺ to Cr³⁺, so the color change should appear at or near the anode and spread into the bulk solution, not at the cathode; Cr³⁺ formation requires the aqueous environment and is pH-dependent, but a visible precipitate need not form within the recorded 10 s.
(ii)Storyline: Frame 1–2: Static shot of transparent cell filled with uniform yellow wastewater; iron and graphite electrodes fully immersed, side-by-side, wired to labeled (+) and (−) terminals of DC supply. Frame 3: Circuit closure action (e.g., switch contact, wire snap-in) visible. Frame 4–10: Gradual emergence of a greenish hue in the solution originating at/around the iron anode and spreading outward; concurrent uniform dulling/corrosion of the iron anode surface; graphite cathode shows no comparable color change; all elements remain in fixed viewpoint with no occlusion, repositioning, or lighting shift.

Manual:
Experimental Procedure
1. Place yellow hexavalent chromium (Cr⁶⁺) wastewater into a transparent electrolysis cell.
2. Immerse iron anode (connected to positive terminal) and graphite cathode (connected to negative terminal) side-by-side at fixed distance.
3. Close circuit to apply stable DC current.
Observation of Experimental Phenomena
- Yellow wastewater gradually develops a greenish hue starting near the iron anode and spreading into the surrounding liquid.
- Iron anode surface dulls or shows a light rust-like film as it corrodes.
- Graphite cathode shows no comparable color change.
Summary of Experimental Principles
- At the anode, Fe⁰ is oxidized to Fe²⁺, which then chemically reduces Cr⁶⁺ to Cr³⁺ (green) in solution (indirect reduction); this is why the color change appears near the anode rather than the cathode.

Prompt Grounding rubric:
level_1: No transparent electrolysis cell is shown; the yellow wastewater is missing; neither the iron anode nor the graphite cathode appears; no DC power supply or terminals are visible; the circuit is never shown closing.
level_2: The transparent cell holding yellow liquid is shown, but the electrodes are missing, both are shown as the same material (e.g., both graphite), or neither connects to a power source; or a power supply appears with no wiring running to either electrode.
level_3: The transparent cell with yellow wastewater, the iron anode, the graphite cathode, and the DC power supply are all shown; the anode connects to the positive terminal and the cathode to the negative terminal; the circuit is shown closing (e.g., a switch flips or a wire is connected); but the electrodes' depth of immersion or their spacing from each other is not shown consistently across the clip.
level_4: Everything required for score 3 holds, and both electrodes stay fully submerged in the wastewater, keep the same side-by-side spacing throughout the clip, and the wiring runs continuously without gaps from the power supply to each electrode, with neither electrode nor wire jumping or vanishing between frames.
level_5: Everything required for score 4 holds, and the whole setup is shown from one unmoving camera position for the entire clip; neither electrode drifts, comes loose, or detaches from its wire; the wiring's contact points with the terminals look the same in every frame; and there is no cut, zoom, or reframing that changes the viewpoint.

Scientific and Causal Correctness rubric:
level_1: The wastewater stays exactly as yellow as it started for the whole clip, with no green tint, cloudiness, or precipitate appearing anywhere, and neither electrode shows any visible change, regardless of whether the circuit is shown closed.
level_2: Some visible change occurs (a color shift, cloudiness, or bubbling appears somewhere), but it is not tied to the circuit: for example the wastewater's color changes before the circuit is closed, a change appears only at the graphite cathode while the iron anode stays untouched, or the wrong color appears (blue, brown, or black) instead of green.
level_3: After the circuit closes, a greenish tint appears in the solution starting at or around the iron anode and gradually spreading into the surrounding liquid; the iron anode's surface visibly dulls or shows a light rust-colored film consistent with corroding; the graphite cathode shows no comparable greening or corrosion; no wrong colors (blue, purple, black) appear anywhere.
level_4: Everything required for score 3 holds, and the greenish color keeps building up gradually rather than appearing all at once, the iron anode's dulling or corrosion visibly progresses further as the clip continues rather than staying static, and the graphite cathode remains visually unchanged in color and surface texture throughout.
level_5: Everything required for score 4 holds, and the green color is never present before the circuit closes and never fades or reverses once it appears; the anode's corrosion advances steadily across its whole submerged surface rather than in random patches; and at no point does any part of the solution or either electrode show a competing color (blue, brown, black, purple); the greenish hue and the anode's dulling are the only changes visible, and they clearly originate at the anode.

Spatiotemporal Consistency rubric:
level_1: The iron anode or the graphite electrode vanishes and reappears, or jumps to a different spot between frames; the liquid's fill level in the cell jumps up or down for no reason; the power supply blinks out of frame and back; the whole cell appears to rotate or resize with no camera movement to explain it; or an electrode appears to float free of its wire.
level_2: The gap between the two electrodes visibly changes from frame to frame even though nothing moves them; the wastewater's surface heaves or wobbles as if the cell were shaken with no cause shown; a wire connection vanishes and reappears with no hand or motion touching it; or the anode and cathode swap left-right positions partway through the clip.
level_3: The electrode positions, the liquid level, and the wiring all look the same throughout, and the cell's lighting does not swing between bright and dark from one frame to the next; but there is one small, noticeable slip (a brief flash of glare hiding part of an electrode for an instant, or a slight unexplained shimmer on the liquid surface) that does not repeat.
level_4: Everything required for score 3 holds, and the electrodes stay rigidly in their side-by-side positions with no perceptible repositioning, the liquid surface stays calm and level in every frame, the wiring stays taut and attached to the same terminals throughout, and the direction of the shadows on the cell and electrodes stays the same from the first frame to the last.
level_5: Everything required for score 4 holds, and there is no visible drift, wobble, or repositioning of either electrode across the entire clip; the liquid surface shows no ripple, splash, or distortion at any point; the wiring's attachment points to the power supply and electrodes look identical in every frame; and the brightness, color, and direction of the lighting and reflections on the cell never noticeably change.