Domain: Natural Science — Environmental Science
Target concept: COD Rapid Determination of Water Quality (Potassium Dichromate Colorimetric Method)

Video generation prompt: Pipette 2 mL of water sample containing COD into a test tube, and add 2 mL of potassium dichromate-sulfuric acid reagent. Heat the mixture in a boiling water bath for 15 minutes.

Evaluation guide:
(i) Target concept: Visual confirmation of redox-driven colorimetric COD determination via dichromate reduction.
Minimum mechanism: Liquid-phase reaction requires physical contact between sample and reagent, followed by thermal activation to drive reduction; color transition must be temporally gated by heating and chemically constrained to orange→green only.
(ii)Storyline: [Frame 0–2] Pipette approaches water sample reservoir → [Frame 3–4] Pipette aspirates liquid with meniscus at 2 mL mark → [Frame 5–6] Pipette moves toward empty test tube → [Frame 7–8] Pipette tip enters tube mouth and dispenses → [Frame 9–10] Test tube now contains orange liquid → [Frame 11–12] Pipette withdrawn, reagent bottle brought near → [Frame 13–14] Reagent added, color remains orange → [Frame 15–16] Test tube placed into boiling water bath with visible steam → [Frame 17–18] Orange gradually shifts to green *only while steam rises continuously* → [Frame 19–20] Green color stabilizes and fills tube uniformly. Perspective: fixed frontal view, shallow depth of field, all critical objects (pipette tip, tube mouth, bath surface) remain fully visible and in-focus throughout.

Manual:
Experimental Procedure
1. Use a calibrated pipette to aspirate exactly 2 mL of water sample.
2. Dispense the sample into a clean glass test tube.
3. Add exactly 2 mL of potassium dichromate-sulfuric acid reagent to the same test tube.
4. Place the test tube vertically into a vigorously boiling water bath.
5. Maintain in bath for duration sufficient to observe color change.
Observation of Experimental Phenomena
- After reagent addition: solution turns uniform orange.
- During boiling: orange color gradually changes to emerald green.
Summary of Experimental Principles
- COD is determined by oxidation of organic matter with potassium dichromate in acidic medium.
- Dichromate (orange, Cr⁶⁺) is reduced to chromium(III) (green, Cr³⁺); color intensity correlates with COD concentration.

Prompt Grounding rubric:
level_1: No pipette, test tube, water sample, or potassium-dichromate/sulfuric-acid reagent is visible; or none of the three core actions (drawing up liquid, adding the reagent, and placing the tube in the boiling bath) ever happen.
level_2: Only one of the following shows up correctly: a pipette with liquid in it, a test tube with liquid in it, or a boiling-water-bath setup; the pipetting action is missing or applied to the wrong container, the reagent is never added or is added to the wrong vessel, or the boiling bath never actually contains a test tube.
level_3: All three core objects are present and identifiable (a graduated handheld pipette, an upright clear test tube, and a boiling water bath with visible steam), and all three actions happen in order (draw up liquid, dispense into the tube, place the tube in the bath); but something is off, such as an unclear volume marking, a volume that doesn't look close to 2 mL, or the pipette tip never actually entering the tube's mouth.
level_4: All core objects are clearly and correctly shown: the pipette's 2 mL mark sits roughly level with the liquid during drawing-up and dispensing; the test tube is empty beforehand and holds a single mixed liquid afterward; the boiling bath is actively bubbling/steaming and covers the lower third of the test tube; the three actions happen in strict order with nothing skipped, reversed, or extra, apart from one small flaw, such as the pipette being held at a slightly off angle, or the steam's density varying a bit from frame to frame without disappearing.
level_5: The pipette draws up liquid to approximately the 2 mL mark (a small, clearly measured volume), then empties it fully into the test tube with the tip inside the opening and no splashing or dripping outside; the test tube is then lowered vertically into the boiling bath, fully submerged and untilted, with steam rising continuously; every object keeps the same appearance, color, and position throughout, with no visible cuts, misalignment, or jumps in time.

Scientific and Causal Correctness rubric:
level_1: No color change happens at all; or the liquid already has color (e.g., blue or green) before the dichromate reagent is added; or the final mixture ends up colorless, black, or yellow, none of which match the orange-to-green transition; or the test tube is never placed in the heating bath.
level_2: A color change happens, but it breaks the expected order: e.g., the color shifts before the reagent is added or before heating starts; or the liquid turns green instantly with no heating step shown; or the orange color is never visible at any point after the reagent is added but before heating begins.
level_3: The liquid turns orange after the reagent is added and stays orange until heating starts; a green color appears only once heating begins and stays visible for at least a second afterward, but the orange and green stages overlap oddly (e.g., green appears while orange is still dominant, or green fades right after heating stops), or the color change happens without any visible steam or bubbling in the bath.
level_4: The liquid is clearly orange right after the reagent is added and before heating starts; green appears only while the bath is actively steaming/bubbling and stays the dominant color through the end of the clip; no other colors (brown, gray, yellow) show up in between; the color looks even throughout the liquid column with no layering or cloudiness, apart from one small deviation, such as green appearing a moment before the steam is visible, or slight cloudiness at the bottom that doesn't affect the overall hue.
level_5: The liquid starts out colorless or faintly yellow, turns distinctly orange as soon as the reagent is added, and stays orange until heating starts; once heating begins (with visible, continuous steam), the color shifts fully and evenly to a green shade with no orange patches left behind, no streaking, no fading, and no reverting back to orange; the color change tracks the heating step closely and holds steady for the rest of the heating phase, with no odd lighting-driven tint or glow.

Spatiotemporal Consistency rubric:
level_1: The pipette or test tube jumps from one position to another with no visible path connecting them (e.g., the pipette appears already inside the test tube); the test tube's position or tilt changes suddenly between frames with no transition; or the lighting switches abruptly from bright to dark with no visible cause.
level_2: The pipette tip disappears just before entering the test tube and reappears already inside it; the test tube rotates more than 90 degrees with no visible turning motion; steam appears fully formed in a single frame with no build-up; or background elements flicker, vanish, or reappear partway through the clip.
level_3: All movement looks continuous and physically plausible: the pipette travels in a straight path toward the test tube's mouth and the tip enters smoothly; the test tube descends into the bath along an unbroken vertical path; steam rises steadily without pulsing or disappearing; minor flaws are still allowed, such as the pipette's shadow briefly vanishing for a frame or two, or the bath water's reflection glitching once.
level_4: All conditions for the 3-score level are met, and in addition: the pipette follows a smooth arc into the tube with no jump or distortion; the test tube's insertion into the bath keeps a consistent vertical alignment and depth; steam rises continuously with a natural, gradually thinning density; shadows, reflections, and any occlusion by the bath's rim stay logically consistent from frame to frame.
level_5: All conditions for the 4-score level are met, and in addition: the pipette tip stays fully visible with correct perspective throughout its approach, entry, and withdrawal; the test tube enters the bath at a constant orientation without wobbling or changing apparent size; steam rises from the bath surface in an organic, irregular pattern rather than a rigid or perfectly uniform plume; shadows match the light source's position, and any reflection in the bath water matches the surface geometry; motion throughout stays smooth with no frozen or repeated moments.