Domain: Natural Science — Chemistry
Target concept: Heating a cobalt(II) complex to induce ligand exchange and reversible color change

Video generation prompt: A glass beaker containing a cobalt(II) chloride aqueous solution was heated on a hot plate and then removed, subsequently cooled to room temperature.

Evaluation guide:
(i) Target concept: Reversible ligand exchange in cobalt(II) complexes driven by thermal dehydration/hydration.
Minimum mechanism: Pink color requires octahedral [Co(H₂O)₆]²⁺; blue color requires tetrahedral [CoCl₄]²⁻; transition must be thermally triggered and fully reversible; aqueous medium and chloride ions must be present for equilibrium.
(ii)Storyline: Phase 1 (Initial state): Pink solution visible in static beaker on ambient-lit surface. Phase 2 (Heating onset): Beaker placed on hot plate → thermal glow appears beneath → pink color gradually replaced by uniform blue across entire liquid volume. Phase 3 (Steady heated state): Blue solution remains stable and uniform while on hot plate. Phase 4 (Removal): Beaker lifted vertically away from hot plate → thermal glow disappears. Phase 5 (Cooling): Blue solution gradually and uniformly reverts to pink over visible duration, ending in stable pink state. All phases occur from fixed frontal viewpoint; no occlusion of liquid surface; lighting remains neutral and diffuse.

Manual:
Experimental Procedure
1. Place a glass beaker containing cobalt(II) chloride aqueous solution (pink) on a hot plate.
2. Heat until color changes from pink to blue.
3. Remove beaker from hot plate and allow to cool to room temperature.
Observation of Experimental Phenomena
The solution reversibly changes from pink (hydrated Co²⁺) to blue (tetrahedral [CoCl₄]²⁻ chloro-complex) upon heating, and reverts to pink upon cooling.
Summary of Experimental Principles
Heating shifts the equilibrium from octahedral [Co(H₂O)₆]²⁺ toward tetrahedral [CoCl₄]²⁻ by ligand exchange with chloride ions already present in solution; cooling restores the hydrated form, reversing the color change. The solution remains aqueous throughout — nothing is literally dehydrated to a solid anhydrous salt.

Prompt Grounding rubric:
level_1: No glass beaker is visible; no cobalt(II) chloride solution is shown; no hot plate appears in frame; the beaker is never placed on or removed from a heat source.
level_2: A glass beaker, a pink or blue liquid, or a hot plate appears, but not combined correctly: e.g., the beaker floats without contacting the hot plate surface, the hot plate is missing while a heat-glow effect appears anyway, or the sequence begins with the beaker being removed and cooled before any heating is ever shown.
level_3: A glass beaker holding a uniformly colored liquid sits on a hot plate; the beaker is shown being placed onto the hot plate (or heating is indicated beneath it) and is later lifted off; no unrelated objects dominate the shot.
level_4: Everything in score 3 holds, and additionally the camera keeps the same fixed framing on the beaker for the whole sequence; the liquid stays inside the beaker the entire time (never disappearing then reappearing); the moment of removal from the hot plate is visually distinct from the still period that follows; no hands, tools, labels, or on-screen text cover the beaker or hot plate.
level_5: Everything in score 4 holds, and additionally the beaker stays centered and at constant size in the frame; the liquid surface is visible and unobstructed before heating, during heating, and after cooling; the whole sequence is one continuous, uncut shot with no zoom, pan, or camera cut.

Scientific and Causal Correctness rubric:
level_1: The liquid's color never changes across the whole sequence, or it changes to a color inconsistent with cobalt(II) chloride chemistry (e.g., turning green, yellow, or black) instead of the pink/blue pair.
level_2: A pink-blue color change occurs, but its timing relative to heat is wrong: e.g., the liquid stays pink for the entire time it sits on the hot plate and only turns blue after the beaker is lifted off and starts cooling, or it turns pink again while the beaker is still on the hot plate before removal; or the liquid starts blue at room temperature and turns pink specifically upon heating (the pink-cold/blue-hot association is reversed).
level_3: The liquid starts pink (hydrated Co²⁺), turns blue while sitting on the hot plate, and turns back to pink after the beaker is lifted off and left to cool; the pink and blue states are each a distinct, recognizable color (not an intermediate purple, lavender, or grey), and each transition occurs in the phase (heating or cooling) it is supposed to.
level_4: Everything in score 3 holds, and additionally the pink-to-blue shift starts only once the beaker is on the hot plate and completes while it is still there; the blue-to-pink shift starts only once the beaker is removed and completes during the cooling period; no in-between shade lingers once each phase has ended.
level_5: Everything in score 4 holds, and additionally each color is even across the whole liquid volume during its phase (no streaks, patches, or partial color pockets); there is no flicker or gradual color drift outside the heating/cooling windows; the pink shade matches typical aqueous cobalt(II) chloride and the blue shade matches the concentrated aqueous [CoCl₄]²⁻ chloro-complex, both viewed under the same ambient white light.

Spatiotemporal Consistency rubric:
level_1: The beaker jumps to a different position or vanishes and reappears between frames; the liquid disappears and reappears in the beaker; the hot plate pops in or out of frame; the room's lighting suddenly switches (e.g., bright to black) with no visible cause; the beaker's glass appears to bend, crack, or melt.
level_2: One or more clear physical-continuity breaks occur: the beaker changes size or shape partway through; the liquid's fill level jumps up or down between consecutive frames instead of changing smoothly; the shadow the beaker casts swings to a different direction even though nothing shows the light source moving; the hot plate's glow appears before the beaker actually touches it, or lingers after the beaker has been lifted away.
level_3: The beaker keeps its shape and size throughout; the liquid's surface stays level with the beaker and never jumps in height; the hot plate stays in the same spot and looks the same throughout; the shadow the beaker casts points the same direction with the same darkness for the whole sequence; nothing flickers, warps, or cracks.
level_4: Everything in score 3 holds, and additionally the beaker's motion is physically believable: it moves straight down onto the hot plate and straight up when lifted off, with no sliding or floating; the liquid surface only ripples during those placement/removal moments, staying flat and still while the beaker is not being moved.
level_5: Everything in score 4 holds, and additionally every motion (placing, heating, lifting, cooling) plays out smoothly with even timing and no stutters or sudden speed changes; the liquid surface is fully still before heating starts and stays still throughout heating; it shows no leftover sloshing or vibration during the cooling phase.