Domain: Natural Science — Chemistry
Target concept: When sulfide is added, copper ions form a black copper sulfide precipitate (chalcocite)

Video generation prompt: Two transparent beakers are placed side by side, each containing the same blue copper ion solution; a colorless sulfide is slowly added to the left beaker, while the right beaker remains unchanged.

Evaluation guide:
(i) Target concept: Precipitation reaction driven by ion combination forming an insoluble binary compound.
Minimum mechanism: Cu²⁺(aq) + S²⁻(aq) → CuS(s); the product must be thermodynamically stable, insoluble, and black under standard conditions; aqueous copper(II) must remain visibly blue prior to reaction; sulfide reagent must be colorless and non-reactive with solvent alone.
(ii)Storyline: Frame 0–2: Two beakers enter view side-by-side, both filled with uniform blue liquid; Frame 3–5: Colorless liquid stream enters frame and contacts left beaker only; Frame 6–8: Black particles nucleate and increase in density within left beaker while blue background remains visible between them; Frame 9–10: Right beaker unchanged: same blue hue, no particles, no motion near it; entire sequence viewed from fixed frontal perspective with full beaker visibility and no occlusion.

Manual:
Experimental Procedure
1. Place two identical transparent beakers side-by-side.
2. Fill both with identical blue copper(II) sulfate solution.
3. Slowly add colorless sodium sulfide solution to the left beaker only.
4. Observe immediately.
Observation of Experimental Phenomena
Left beaker: blue solution develops black particulate precipitate that settles; right beaker: remains uniformly blue with no precipitate.
Summary of Experimental Principles
Copper ions (Cu²⁺) react with sulfide ions (S²⁻) to form insoluble black copper(II) sulfide (CuS), a characteristic precipitation reaction in qualitative inorganic analysis.

Prompt Grounding rubric:
level_1: No two beakers visible; or only one beaker present; or beakers not side-by-side; or no blue solution in either beaker; or sulfide addition not depicted at all.
level_2: Two beakers are present and side-by-side, but at least one lacks blue solution; or sulfide is added to both beakers; or sulfide is added to the right beaker only; or sulfide is added before both beakers are fully visible.
level_3: Two transparent beakers are side-by-side and both contain visibly blue liquid; sulfide is added only to the left beaker; right beaker remains unchanged throughout; no other containers or interfering objects dominate the frame.
level_4: All conditions for score 3 are met, and sulfide addition is clearly depicted as a distinct action (e.g., dropper/pipette entering frame or liquid stream visible) targeting only the left beaker; right beaker shows zero intervention: no motion toward it, no tool proximity, no visual cue of addition.
level_5: All conditions for score 4 are met, and the sulfide addition is visually unambiguous: a colorless liquid or solution is seen entering the left beaker (e.g., clear stream/droplets), with no ambiguity about source, trajectory, or target; right beaker remains completely static and isolated: no shared tool contact, no overlapping motion paths, no temporal overlap between addition action and right-beaker region.

Scientific and Causal Correctness rubric:
level_1: No color change occurs; or black precipitate appears in right beaker; or left beaker turns a color other than black (e.g., green, brown, purple, gray); or blue color disappears without black solid formation.
level_2: Black precipitate forms in left beaker, but blue color fully vanishes before black appears (i.e., no coexistence of blue solution and black solid); or black precipitate appears simultaneously in both beakers; or black material forms but is suspended uniformly (no particulate settling or cloudiness).
level_3: Left beaker shows emergence of black particulate matter within blue solution; black solid is visibly distinct from background blue liquid; right beaker retains uniform blue color with no black particles or discoloration; black precipitate does not appear before sulfide addition begins.
level_4: All conditions for score 3 are met, and black precipitate is confined exclusively to left beaker; no black particles migrate, float into, or adhere to right beaker’s walls or surface; left beaker’s blue color persists around black particles (i.e., solution remains translucent blue with opaque black solids dispersed/sedimenting).
level_5: All conditions for score 4 are met, and black precipitate exhibits characteristic appearance: granular, matte, non-reflective, and clearly insoluble; no dissolution, no sheen, no dispersion into colloidal haze; blue solution remains visibly homogeneous *between* particles, confirming copper ion presence coexisting with CuS solid; no fading, bleaching, or dilution of blue hue in left beaker unrelated to particle coverage.

Spatiotemporal Consistency rubric:
level_1: Beakers teleport between frames; or sudden size/position shift; or abrupt lighting change (e.g., flash, total darkening); or beaker geometry distorts (e.g., bending, warping); or liquid surface discontinuously jumps.
level_2: Beakers remain fixed in position but show inconsistent lighting (e.g., specular highlight appears/disappears erratically); or sulfide addition motion is jerky or segmented (≥2 disjoint motion events with pause >0.5s implied by frame gaps); or black precipitate appears instantaneously without progressive onset (i.e., fully formed in single frame).
level_3: Both beakers maintain stable position, shape, and orientation; lighting is consistent across all frames; sulfide addition is a continuous, unbroken motion toward left beaker; black precipitate emerges gradually, visible as increasing density/coverage of black particles over ≥3 consecutive frames.
level_4: All conditions for score 3 are met, and motion parallax is natural: tool movement follows smooth trajectory with no acceleration anomalies; liquid surface ripples (if any) propagate plausibly from impact point; black particles settle downward with consistent directionality and no upward drift or floating.
level_5: All conditions for score 4 are met, and spatial integrity is perfect: no interpenetration between beaker walls and particles/tool; no clipping of tool tip or droplets at beaker rim; no occlusion errors (e.g., black particles appearing behind beaker wall); no frame duplication, ghosting, or temporal stutter; every frame advances causally and continuously.