Domain: Natural Science — Chemistry
Target concept: Reaction of chlorine water with potassium iodide

Video generation prompt: Place the test tubes side by side; add chlorine water to the potassium iodide solution in the test tube, then add carbon tetrachloride to induce layering.

Evaluation guide:
(i) Target concept: Halogen displacement redox reaction coupled with solvent extraction-based visualization.
Minimum mechanism: Chlorine must be present to oxidize iodide ions; iodine molecules must form and partition preferentially into carbon tetrachloride due to polarity mismatch; density difference must drive phase separation with CCl₄ as lower layer.
(ii)Storyline: Frame 0–2: Two empty test tubes placed side-by-side in fixed frontal view. Frame 3–4: Chlorine water bottle approaches and dispenses into left test tube (containing colorless KI solution). Frame 5–6: No color change in aqueous phase. Frame 7–8: Carbon tetrachloride bottle approaches and dispenses into same test tube. Frame 9–10: Visible mixing (implied), followed by rapid phase separation: upper layer clears to colorless, lower layer develops a violet-to-purple color with sharp horizontal interface; right test tube remains unchanged as control. Perspective remains static frontal; all critical events occur within field of view without occlusion.

Manual:
Experimental Procedure
1. Place two identical test tubes side-by-side in a test tube rack.
2. Add chlorine water dropwise to the first test tube containing potassium iodide solution.
3. Add carbon tetrachloride to the same test tube.
4. Gently shake and allow layers to separate.
Observation of Experimental Phenomena
The upper aqueous layer becomes colorless (or pale yellow); the lower carbon tetrachloride layer turns violet-to-purple due to extracted iodine.
Summary of Experimental Principles
Cl₂ oxidizes I⁻ to I₂; I₂ is more soluble in CCl₄ than in water, so it partitions into the lower organic layer. Because CCl₄ is non-polar, dissolved I₂ shows its characteristic violet-to-purple color there, rather than the brown/amber color I₂ (as I3⁻) can show in polar water.

Prompt Grounding rubric:
level_1: No test tubes appear on screen; none of the required bottles (chlorine water, potassium iodide solution, carbon tetrachloride) are shown; the two tubes are not shown next to each other; no pouring or addition of any liquid is depicted.
level_2: Two tube-like transparent containers appear next to each other, but one of the three reagents (chlorine water, KI solution, or CCl4) is missing entirely, or a liquid is poured into the wrong container, or it is unclear which container receives which liquid; no two-layer appearance results.
level_3: Two test tubes are shown side by side in the same shot; a bottle recognizable as chlorine water is shown pouring into the tube holding the colorless KI solution; afterward a bottle recognizable as carbon tetrachloride is poured into that same tube; two distinct liquid layers become visible in that tube.
level_4: All elements of score 3 are present AND: both test tubes stay in frame and upright the entire time; chlorine water is added only to the KI-containing tube, never to the other tube; CCl4 is added only after the chlorine water; the second (control) tube is never touched and stays visually unchanged; no unrelated objects or hands interfere with either addition.
level_5: All elements of score 4 are present AND: each bottle is held steadily and pours with a controlled, visible stream landing inside the target tube rather than beside it or in mid-air; both test tubes keep the same size, angle, and lighting relative to each other across the whole clip; no extra object enters or leaves the frame during the sequence; the contents of both tubes stay visible and unobstructed during and after each addition.

Scientific and Causal Correctness rubric:
level_1: No color change appears in either the aqueous KI layer or the CCl4 layer; the liquid remains a single colorless phase throughout, with no evidence that iodine has formed or migrated into the carbon tetrachloride.
level_2: A color appears somewhere in the tube, but not the correct one for this reaction: e.g., the aqueous (upper) layer turns deep brown/black, or the lower CCl4 layer stays colorless, or the lower layer turns amber/orange-brown instead of violet-to-purple; or only one layer is visible with no distinguishable second phase.
level_3: After chlorine water is added, the aqueous KI solution may show a faint yellow-brown tint; after CCl4 is added and the tube settles, two layers are visible with the lower, denser layer showing a violet-to-purple color characteristic of iodine dissolved in CCl4, while the upper aqueous layer is colorless to pale yellow.
level_4: All elements of score 3 are present AND: the violet-to-purple color is confined to the lower CCl4 layer only, with no violet/purple tint bleeding into the upper aqueous layer; the upper layer is colorless or only faintly pale yellow with no purple cast; the control (second) test tube shows no color change; the color only appears after CCl4 is added, not immediately after chlorine water alone.
level_5: All elements of score 4 are present AND: the lower CCl4 layer is a strong, saturated violet-to-purple with a sharp, stable interface against the upper layer; the upper aqueous layer is clear and colorless with no cloudiness; no purple color leaks across the interface into the aqueous layer over the course of the video; the color intensity in the CCl4 layer does not fade or bleed during the remaining observation time.

Spatiotemporal Consistency rubric:
level_1: Test tubes jump to different positions or sizes between frames; the room lighting switches from fully lit to dark with no transition; a liquid layer appears or disappears from one frame to the next without any pouring action; the interface between layers snaps into place instantly with no settling motion visible.
level_2: The two test tubes shift from side-by-side to a stacked or offset arrangement partway through the clip; the camera angle changes abruptly during a pour (e.g., jumping from a side view to looking down into the tube); the two liquid layers appear separated without any preceding mixing or swirling; the glass walls of a test tube visibly bend or shear between frames.
level_3: The two test tubes stay in the same side-by-side arrangement for the entire clip; each pour (chlorine water, then CCl4) proceeds as one continuous stream from bottle tip into the tube opening; the liquid stream keeps a steady thickness and path rather than cutting on and off; the violet-to-purple lower layer forms gradually, with a visible settling period and a meniscus, rather than snapping into place; no test tube blinks out of view or reappears at any point.
level_4: All elements of score 3 are present AND: the two test tubes stay at the same apparent distance from the camera throughout; the pouring motion neither freezes nor suddenly speeds up; there is no stutter or repeated frame; the direction and strength of shadows cast by the test tubes stay the same before and after each addition; the glass of the test tubes shows no warping or curvature change near the edges.
level_5: All elements of score 4 are present AND: the liquid stream during each pour is smooth and unbroken, without splattering or pulsing; the violet-to-purple CCl4 layer settles with a continuous downward motion while the aqueous layer above clarifies at the same time; the test tubes show no visible shaking or vibration once pouring stops; reflections of light on the glass and liquid surfaces stay consistent in position and brightness across the remaining frames.