Domain: Natural Science — Chemistry
Target concept: Equilibrium color change of cobalt chloride upon addition of water or heating

Video generation prompt: Display a transparent container filled with a concentrated cobalt chloride solution in hydrochloric acid on the laboratory bench, add water to it, and then gently place the same container on a hot plate for heating.

Evaluation guide:
(i) Target concept: Reversible chloro/aqua ligand-exchange equilibrium of cobalt(II) in concentrated hydrochloric acid, shifted by water addition and by thermal removal of water.
Minimum mechanism: Co²⁺ ions coordinated by either Cl⁻ ligands (blue, tetrahedral [CoCl₄]²⁻, favored when chloride is concentrated) or H₂O ligands (pink, octahedral [Co(H₂O)₆]²⁺, favored once water dilutes the chloride); the coordination change must be visually encoded as discrete, uniform, and causally bound color states.
(ii) Storyline: Phase 1 (0–3s): Static shot of the transparent container on the bench, containing a blue, concentrated cobalt chloride solution in hydrochloric acid; the background is visible through the container's walls. Phase 2 (3–6s): A hand enters frame holding a water source (e.g., dropper/bottle) and delivers water into the container; the solution visibly transforms from blue to uniform pink within the same container, with no mixing artifacts. Phase 3 (6–10s): The hand lifts the container and places it flat on the hot plate's surface; upon contact and sustained heating, water evaporates from the solution and it transforms back from pink to uniform blue; all transitions occur within a fixed frontal lab perspective, and the container never leaves the frame or loses full visibility.

Manual:
Experimental Procedure
1. Place a transparent container (e.g., glass beaker) filled with a blue, concentrated cobalt chloride solution in hydrochloric acid on a laboratory bench.
2. Add water to the container; as the water dilutes the chloride concentration, the solution turns uniformly pink.
3. Gently lift the container and place it centrally on a hot plate; heat until the water evaporates and the solution turns uniformly blue again.
Observation of Experimental Phenomena
- Initial state: blue color (tetrahedral [CoCl₄]²⁻ complex, favored in the concentrated hydrochloric acid).
- After water addition: rapid, uniform color change to pink (octahedral [Co(H₂O)₆]²⁺ complex forms as the chloride is diluted).
- After heating: gradual, uniform color reversion to blue (water evaporates, the chloride re-concentrates, and the tetrahedral complex is restored).
Summary of Experimental Principles
Cobalt(II) in concentrated hydrochloric acid shows a reversible ligand-exchange equilibrium: [CoCl₄]²⁻ (blue, tetrahedral) + 6H₂O ⇌ [Co(H₂O)₆]²⁺ (pink, octahedral) + 4Cl⁻. Adding water dilutes the chloride and drives the equilibrium right (pink); heating evaporates the water, re-concentrating the chloride and driving the equilibrium left (blue).

Prompt Grounding rubric:
level_1: No transparent container appears at any point; no cobalt chloride solution is shown inside it; no water is poured in; no hot plate appears; no heating action is shown; none of the three required elements (container with solution on the bench, the water-addition step, the hot-plate heating step) is present in the video.
level_2: Only one of the three required elements is present (e.g., the container and its solution appear but no water is ever added, or a hot plate appears but heating never actually starts); or the three steps appear out of order (e.g., the container is already on the hot plate before ever being shown on the bench); or a required object is swapped for something incompatible with the demo (e.g., an opaque ceramic mug stands in for the transparent container, so the solution inside can never be seen).
level_3: All three required elements appear: a transparent container holding the cobalt chloride solution, and a hot plate; the container is first shown resting on the bench; water is then poured into the container (a visible stream or drops entering the liquid); the container is then moved onto the hot plate; the three steps occur in this order; no object is substituted for an incompatible one (e.g., the water source is not mislabeled as some other reagent, and the heating surface is recognizable as a hot plate rather than an open flame or stove burner).
level_4: All conditions for score 3 are met, AND the same physical container is used throughout (it is not swapped for a different beaker or flask between the bench, water-addition, and hot-plate shots); the poured water visibly lands inside the container's mouth rather than beside it or hovering above it; when the container reaches the hot plate, its base visibly rests flat against the hot plate's surface; no shot consists only of a hand or water stream with the container itself out of frame.
level_5: All conditions for score 4 are met, AND the bench-to-water-addition-to-hot-plate sequence reads as one continuous action (via a single take or cuts that preserve the container's position and orientation, with no jarring jump where the container's location changes without a corresponding move being shown); the container stays centered and fully in view across all three phases; the hand that pours the water and the hand that places the container on the hot plate both move with clear, deliberate intent (entering frame, performing the action, then exiting); at no point does the container appear twice at once, get blocked from view by an unrelated object, or get treated as the wrong kind of vessel.

Scientific and Causal Correctness rubric:
level_1: The cobalt(II) chloride solution shows no visible color shift across the water-addition and heating steps (e.g., it stays blue, or stays pink, the whole time), or it shifts to a color inconsistent with cobalt(II) chloro/aqua chemistry (e.g., green, orange, or yellow), or the container holds only a dry powder with no liquid ever visible.
level_2: A blue-to-pink-to-blue color shift is present but breaks the causal order tied to this demo: pink appears before any water is poured in, or the return to blue appears before the container is heated on the hot plate; or the color shifts while the container sits untouched on the bench with no water or heat applied; or the water-addition step shows only clear, colorless liquid entering with no color change at all despite visible pouring.
level_3: Solution starts blue in the container on the bench (the tetrahedral chloro-cobalt complex in the concentrated hydrochloric acid); once water is poured in, the solution turns uniformly pink (the aqua-cobalt complex forming as the chloride is diluted); once the container is heated on the hot plate, the solution returns to uniform blue (water driven off, the chloro complex reforming); all three color states occur in this order and each is tied to the action that caused it; no unrelated colors (e.g., purple, brown, orange) appear in the solution at any point.
level_4: All conditions for score 3 are met, AND each color change begins only once its triggering action is complete or clearly underway: the shift to pink starts only after water has entered the container (not mid-pour, before the water lands); the shift back to blue starts only once the container has been heating on the hot plate for a visible interval (e.g., after steam or a heat shimmer appears above the solution); the solution never shows two different colors in different parts of the same liquid at once (e.g., no pink top layer sitting above an unmixed blue bottom layer).
level_5: All conditions for score 4 are met, AND the two colors read as chemically distinct and correctly saturated: the blue state reads as a clear, cool blue (not violet-tinted or grayish); the pink state reads as a warm rosy pink or magenta (not pale lavender or orange-salmon); each color change sweeps through the entire visible solution volume evenly, with no streaking or patchy gradients as it happens; once the solution has fully turned blue again at the end of heating, no leftover pink patches or tinting remain anywhere in the container.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal rupture: the container vanishes from one frame and reappears elsewhere without ever being carried there; the container's orientation flips or rotates instantaneously between frames with no visible motion carrying it there; the solution's liquid level jumps up or down between frames with no corresponding pour or heating event; the hot plate appears in frame or disappears from frame without the camera or container ever moving past it; the container's shape breaks apart and reforms (e.g., it appears to shatter and then is instantly intact again).
level_2: Moderate discontinuity: the container's size or shape changes between the bench shot and the hot-plate shot (e.g., a wide beaker on the bench becomes a narrow test tube on the hot plate); the solution's liquid level changes in a way not explained by the visible water addition or heating (e.g., it rises with no water shown entering, or drops with no steam or evaporation cue); the hot plate's surface or knob orientation is inconsistent between the moment the container is placed on it and later in the heating phase; the lab's light source or the container's cast shadow shifts direction or brightness between the bench shot and the hot-plate shot with no corresponding change in the room or in the heating element to explain it.
level_3: The container's size, shape, and orientation stay the same from the bench shot through the water-addition shot to the hot-plate shot, and it never appears in two places at once; the solution surface stays flat and undisturbed except for the ripples from the incoming water and the faint shimmer once heating begins; any change in the scene's brightness or in the container's cast shadow only happens when the hot plate visibly starts glowing or heating (not at some unrelated moment); the container travels from bench to hot plate along a single visible path, without jerking, floating unsupported, or passing through the bench or hot-plate surface.
level_4: All conditions for score 3 are met, AND all motion in the scene is physically plausible: the poured water falls straight down into the container's mouth rather than arcing sideways or hanging motionless in the air; when the container is set down on the hot plate, it decelerates smoothly to a stop rather than bouncing or sliding across the surface; the container's walls do not stretch, bulge, or squash while it is being carried or set down; the visible duration of the water pour and of the hand's carrying motion matches the speed of the liquid and the hand (no unnaturally sped-up or slowed-down segment).
level_5: All conditions for score 4 are met, AND the whole sequence holds together as one coherent physical scene: the container's base stays fully and flatly seated on the hot plate for the entire heating phase, without sliding, tilting, or lifting off; the curved meniscus of the solution's surface stays visible and consistent in shape while the color change happens; the container and the hand handling it stay in correct size relative to the bench and hot plate throughout (neither growing nor shrinking relative to its surroundings); the transition between the bench shot, the water-addition shot, and the hot-plate shot never skips or repeats a moment of the action (e.g., the water is never shown landing in the container twice, and the placement onto the hot plate is never shown out of order).