Domain: Natural Science — Chemistry
Target concept: Cobalt(II) Chloride Hydration Equilibrium: The Pink-Blue Color Transition Accompanying the Change in Hydration Status

Video generation prompt: A transparent glass test tube containing a cobalt(II) chloride solution was alternately placed in a hot water bath and an ice water bath on the laboratory bench.

Evaluation guide:
(i) Target concept: Reversible, temperature-driven hydration equilibrium of CoCl₂ in aqueous solution, manifested as binary pink/blue color transition.
Minimum mechanism: Aqueous Co²⁺ must be present in dynamic ligand exchange environment; thermal energy must drive ligand displacement (H₂O ↔ Cl⁻) without decomposition; glass container must permit unobstructed color observation; solution must be dilute enough to avoid precipitation and concentrated enough for vivid color.
(ii)Storyline: Frame 1–3: Static shot of test tube on bench beside two adjacent baths (hot left, ice right). Frame 4–6: Hand places test tube into hot bath → liquid becomes uniformly blue within immersion. Frame 7–8: Hand removes test tube → blue persists briefly. Frame 9–10: Test tube placed into ice bath → liquid becomes uniformly pink within immersion. Perspective: Fixed frontal bench-level view; full test tube always in frame; no occlusion; color change must occur only during active immersion, never during transfer.

Manual:
Experimental Procedure
1. Place a transparent glass test tube containing aqueous cobalt(II) chloride solution on a laboratory bench.
2. Submerge the test tube fully into a hot water bath for several seconds.
3. Remove and immediately submerge it fully into an ice water bath for several seconds.
Observation of Experimental Phenomena
The solution reversibly changes from blue (in hot water bath) to pink (in ice water bath) — color shift is sharp, complete, and correlates precisely with bath immersion.
Summary of Experimental Principles
Cobalt(II) chloride exists in equilibrium between hydrated [Co(H₂O)₆]²⁺ (pink) and dehydrated [CoCl₄]²⁻ (blue) forms; cooling favors hydration (pink), heating favors dehydration (blue).

Prompt Grounding rubric:
level_1: No transparent glass test tube visible; no hot water bath or ice water bath present; no laboratory bench setting; no alternation between two baths; core objects (test tube, baths) entirely absent.
level_2: At least one of the three core objects appears (test tube OR hot water bath OR ice water bath), but none are simultaneously present; no alternation action shown; laboratory bench not established as background context.
level_3: Transparent glass test tube AND at least one bath (hot OR ice) AND laboratory bench are all present and visibly co-located in same scene; alternation is implied by presence of both baths side-by-side, but no visible placement action of the test tube into either bath.
level_4: Transparent glass test tube, hot water bath, ice water bath, and laboratory bench are all present and co-located; test tube is visibly placed into one bath, then removed and placed into the other bath; sequential placement action is fully shown; no teleportation or discontinuity in test tube position between placements.
level_5: All elements from score 4 are present AND the test tube remains continuously visible throughout the entire sequence (no occlusion, no cut-away, no disappearance); placement into hot bath occurs first, followed by placement into ice bath; correct order matches posted_prompt; both baths are adjacent and clearly distinguishable by visual cues (e.g., steam vs. condensation/frost), confirming side-by-side spatial relationship.

Scientific and Causal Correctness rubric:
level_1: No color change observed; test tube contents remain constant pink or constant blue or unidentifiable color throughout; no hydration equilibrium phenomenon visually represented.
level_2: Color change occurs but in wrong direction (e.g., pink → pink, blue → blue, or blue → pink when heated); or color change coincides with incorrect bath (e.g., pink appears during hot bath exposure); or color is non-chemically plausible (e.g., green, yellow, opaque).
level_3: Color change occurs: solution is pink when in ice water bath AND blue when in hot water bath; both colors are visually distinct and consistent with cobalt(II) chloride hydration states; however, the color transition is not temporally aligned with bath placement (e.g., color changes before placement or after removal).
level_4: Color change is correctly directionally aligned: solution appears pink during full immersion in ice water bath AND blue during full immersion in hot water bath; color state is stable and sustained while immersed; no intermediate or mixed colors appear during immersion; causal link between bath type and color is visually unambiguous.
level_5: All conditions from score 4 are satisfied AND color transition occurs only upon immersion (not before or after); pink and blue states are pure, saturated, and fully cover the visible liquid volume without streaking, clouding, or phase separation; no residual color memory (e.g., no pink tint remaining after hot bath exposure); color states are mutually exclusive and never co-occur in the same frame during immersion.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal breakdown: test tube teleports between locations; abrupt light/shadow jumps; sudden scale/rotation changes; structural break in test tube (e.g., split, warp, vanish); frames freeze or skip unpredictably.
level_2: Major discontinuities: test tube disappears for ≥1 continuous frame during motion; lighting shifts abruptly between shots (e.g., warm → cool without transition); visible jump-cut between bath placements; bench surface geometry distorts across frames.
level_3: Minor but detectable artifacts: brief flicker during color transition; slight jitter in test tube position during stationary phases; minor shadow inconsistency under static lighting; no teleportation or structural breaks; motion is continuous but not perfectly smooth.
level_4: All motion is continuous and physically plausible: test tube moves smoothly into and out of baths; no frame drops, no jitter, no lighting jumps; shadows and reflections remain consistent with fixed viewpoint and static lighting; bench surface and bath containers retain stable geometry and alignment.
level_5: All conditions from score 4 are met AND camera viewpoint remains absolutely fixed (no pan/tilt/zoom); test tube maintains consistent orientation and depth relation to bench surface throughout; reflections on glass test tube and bath surfaces evolve naturally with motion; no inter-frame misalignment of object edges or parallax shifts.