Domain: Natural Science — Chemistry
Target concept: Reaction between copper sulfate and sodium hydroxide

Video generation prompt: A test tube contains a blue copper(II) sulfate solution. A colorless sodium hydroxide solution is added using a pipette, and the test tube remains undamaged.

Evaluation guide:
(i) Target concept: Precipitation reaction producing insoluble copper(II) hydroxide via double displacement.
Minimum mechanism: Aqueous Cu²⁺ ions must encounter OH⁻ ions to nucleate and grow Cu(OH)₂ solid phase; reaction must occur in solution phase without thermal decomposition or side redox; glass container must withstand mild exotherm and mechanical stability of mixing.
(ii)Storyline: [Frame 0–2] Static shot: upright test tube centered, filled ~2/3 with homogeneous blue liquid; pipette held stationary above opening. [Frame 3–4] Pipette descends smoothly; colorless liquid begins exiting tip as coherent stream. [Frame 5] First contact: stream meets blue liquid surface → localized turbidity appears instantly. [Frame 6–8] Pale blue flocs expand downward and outward from impact zone; supernatant remains translucent. [Frame 9–10] Final state: stable suspension of pale blue precipitate in faintly blue supernatant; test tube fully intact, no overflow, no tilt. Perspective: fixed frontal view, eye-level to test tube midpoint; full test tube and pipette tip always in frame; no occlusion.

Manual:
1. Place a clean, upright test tube containing aqueous copper(II) sulfate solution (distinctly blue).
2. Hold a pipette filled with colorless sodium hydroxide solution above the test tube opening.
3. Dispense the sodium hydroxide solution into the test tube — contact occurs, forming an immediate pale blue precipitate while the test tube remains intact.
Observation: Blue solution + colorless liquid → immediate formation of fluffy pale blue precipitate suspended in solution; no color change to green/black/brown; test tube undamaged.
Principle: CuSO₄(aq) + 2NaOH(aq) → Cu(OH)₂(s)↓ + Na₂SO₄(aq); Cu(OH)₂ is an insoluble pale blue solid.

Prompt Grounding rubric:
level_1: No test tube present; or no blue liquid visible in test tube; or no pipette present; or no colorless liquid visibly dispensed from pipette; or test tube visibly cracked, shattered, or deformed.
level_2: Test tube is present and intact, and contains a liquid, but the liquid is not blue; OR pipette is present and dispenses liquid, but the dispensed liquid is not colorless; OR blue liquid and colorless liquid are both present but no contact occurs between them within the video.
level_3: Test tube is present and intact, contains a clearly blue liquid; pipette is present and dispenses a clearly colorless liquid into the test tube; contact between the two liquids occurs inside the test tube; no structural damage to test tube is visible at any frame.
level_4: All conditions for score 3 are satisfied, AND the pipette tip remains outside the test tube during dispensing (i.e., no insertion of pipette into liquid column), AND the blue liquid occupies the majority of the test tube volume before addition, AND the colorless liquid is dispensed as a distinct stream (not splashed, dripped erratically, or misted).
level_5: All conditions for score 4 are satisfied, AND the pipette is held vertically above the test tube opening with steady hand-like motion, AND the blue liquid surface remains undisturbed until the moment of first contact, AND the test tube maintains fixed upright orientation throughout, AND no visual artifact (e.g., flicker, cut, warp) interrupts the dispensing-to-contact transition.

Scientific and Causal Correctness rubric:
level_1: No color change observed after contact; or precipitate appears but is not pale blue; or precipitate appears but remains suspended without settling; or final mixture is uniformly green, purple, black, or white, none of which correspond to copper(II) hydroxide formation.
level_2: Contact occurs, but no precipitate forms; OR precipitate forms but is not pale blue; OR precipitate forms but appears granular, crystalline, or fibrous rather than fluffy and amorphous; OR blue color of solution disappears without precipitate formation.
level_3: Contact between blue copper(II) sulfate solution and colorless sodium hydroxide solution occurs, and a pale blue precipitate appears within the liquid column; the original blue solution remains visibly present around the precipitate; no other colors (e.g., green, brown, black) appear in the precipitate or supernatant.
level_4: All conditions for score 3 are satisfied, AND the pale blue precipitate forms immediately upon contact (no delay >1 visual continuity interval), AND the precipitate remains confined within the test tube (no overflow or ejection), AND the supernatant above the precipitate remains transparent and colorless or faintly blue (not cloudy white or yellow).
level_5: All conditions for score 4 are satisfied, AND the pale blue precipitate exhibits soft, flocculent morphology (not sharp-edged, not gelatinous, not sedimented into a compact layer), AND the boundary between precipitate and supernatant is diffuse and evolving (not sharply stratified or static), AND no dissolution, re-suspension, or color shift of precipitate occurs during observation.

Spatiotemporal Consistency rubric:
level_1: Test tube disappears and reappears; or pipette jumps between locations; or liquid changes volume/shape discontinuously (e.g., instant full fill); or lighting changes abruptly mid-sequence; or test tube rotates >30° without smooth motion.
level_2: Test tube wobbles or shifts position more than once without clear cause; or pipette motion is jerky or non-continuous; or liquid surface shows unnatural ripple freeze or oscillation; or shadow on test tube changes direction inconsistently across frames.
level_3: Test tube remains in fixed position and orientation; pipette moves continuously from above toward test tube opening; liquid level rises smoothly during dispensing; no object teleportation, no abrupt lighting shift, no structural warping or stretching of test tube or liquid.
level_4: All conditions for score 3 are satisfied, AND pipette motion is monotonic downward (no upward correction or hesitation), AND liquid stream maintains consistent width and trajectory from pipette tip to impact point, AND precipitate formation propagates downward from contact zone without lateral jump or fragmentation.
level_5: All conditions for score 4 are satisfied, AND motion parallax between foreground (pipette tip) and background (test tube wall) is visually consistent; AND no inter-frame flicker, ghosting, or motion blur that obscures object boundaries; AND temporal flow is unbroken (no cuts, dissolves, or frame drops), and all transitions (contact → turbidity → precipitation) occur in single continuous take.