Domain: Engineering — Food and Bioprocess Engineering
Target concept: Determination of Copper in Food by Sodium Diethyldithiocarbamate Method

Video generation prompt: Take 2 mL of pig liver extract and place it in a test tube, then add sodium diethyldithiocarbamate solution.

Evaluation guide:
(i) Target concept: Visual verification of copper detection via Cu-DDTC chelation reaction.
Minimum mechanism: Pig liver extract must contain bioavailable Cu²⁺; sodium diethyldithiocarbamate must be chemically intact and reactive; aqueous environment enables rapid ligand exchange; color development requires stoichiometric complex formation, not dilution or oxidation artifact.
(ii)Storyline: Frame 1–2: Static shot of labeled test tube containing amber-brown liquid (pig liver extract), occupying lower third of tube, meniscus stable. Frame 3–4: Dropper with colorless-to-pale-yellow sodium diethyldithiocarbamate solution enters from top-right, aligns precisely with tube mouth. Frame 5: First droplet contacts surface; immediate localized color shift at impact zone. Frame 6–7: Color propagates radially and uniformly upward through liquid column. Frame 8–10: Fully homogenized yellow-brown solution with stable meniscus; no residual amber-brown zones or interface lines. Perspective: Fixed frontal close-up (tube fills ≥70% height), shallow depth of field isolating tube/dropper, consistent overhead diffuse lighting to reveal hue and transparency.

Manual:
Experimental Procedure
1. Place 2 mL pig liver extract into a clean test tube.
2. Add sodium diethyldithiocarbamate solution dropwise into the same test tube.
Observation of Experimental Phenomena
Amber-brown pig liver extract turns uniformly yellow-brown upon reagent addition, indicating Cu-DDTC complex formation.
Summary of Experimental Principles
Copper ions in the sample chelate with sodium diethyldithiocarbamate to form a stable yellow-brown complex, enabling spectrophotometric quantification.

Prompt Grounding rubric:
level_1: No test tube is visible, no amber-brown pig liver extract is shown inside any container, no sodium diethyldithiocarbamate solution or dropper appears, and no dispensing action occurs; none of the objects or steps named in the prompt are depicted.
level_2: Only one core element from the prompt appears (e.g., an empty test tube, or a liquid-filled container never identified as pig liver extract, or a dropper/vial that never approaches the tube); the extract is never shown inside the test tube, or the reagent is never dispensed into it, so the fill-then-add sequence does not occur.
level_3: A test tube holding an amber-brown liquid consistent with pig liver extract is shown, and a separate dropper or vial dispenses a liquid into that same tube; the roughly 2 mL fill level is plausible from the lower-third liquid column, but the dispensed liquid's color or clarity does not clearly read as sodium diethyldithiocarbamate solution (e.g., it looks opaque, an implausible color, or comes from an unlabeled, ambiguous container), so the reagent's identity is not confidently confirmed by sight.
level_4: The test tube already contains the amber-brown pig liver extract, occupying roughly the lower third of the tube, before any reagent is added; a dropper or vial then dispenses a visibly colorless-to-pale liquid consistent with aqueous sodium diethyldithiocarbamate into the same tube, in that order (extract first, reagent second); the dispensing action is unambiguous, with the dropper tip approaching and releasing near the tube mouth.
level_5: The test tube contains the amber-brown pig liver extract at a fill level consistent with about 2 mL before addition; a labeled dropper or vial dispenses a clearly colorless-to-pale-yellow sodium diethyldithiocarbamate solution with clean tip-to-mouth contact and no spillage outside the tube; the extract and reagent remain visually distinguishable as two liquids for at least half a second before mixing begins; every object, the implied quantity, and the extract-then-reagent order match the posted prompt exactly.

Scientific and Causal Correctness rubric:
level_1: No color change occurs after the reagent is added, or the mixture ends colorless or white, or it shows a hue with no basis in copper-dithiocarbamate chemistry (e.g., it turns blue, purple, or red); there is no visible link between adding the reagent and any color shift.
level_2: A color change occurs, but the resulting hue is clearly wrong for the Cu-DDTC complex (e.g., the mixture turns blue, pink, or gray rather than any brown or yellow tone), or the shift begins before the reagent contacts the liquid, or the color is identical whether or not the reagent is shown being added.
level_3: After reagent addition, the mixture shifts toward a brownish or yellow-brown tone broadly consistent with the Cu-DDTC complex, but the color is patchy, faded, or unevenly distributed through the liquid column (e.g., darker near the surface than at the bottom), and it develops slowly relative to how much reagent is shown entering.
level_4: After reagent addition, the mixture develops an even yellow-brown color throughout the liquid column, consistent with the Cu-DDTC complex, with no residual amber-brown streaks and no incorrect competing hues (e.g., no blue or purple tint); the liquid stays clear rather than cloudy, and the color change is clearly triggered by, and only by, the reagent's arrival.
level_5: The full liquid column transitions within about a second of reagent contact, turning uniformly from the original amber-brown pig liver extract to a saturated yellow-brown color matching the documented Cu-DDTC complex, with no patch of the original amber-brown remaining anywhere, no cloudiness or sediment, and the transition visibly begins only once the reagent contacts the liquid and settles without drifting toward green, blue, or gray.

Spatiotemporal Consistency rubric:
level_1: The test tube or dropper vanishes and reappears between shots, the amber-brown liquid or the added reagent jumps between containers with no visible pour, the scene cuts from a bright frame straight to a black one with no transition, or the tube's shape breaks (e.g., bends or splits) mid-clip.
level_2: The test tube shifts to a new position or rotates more than about 30° with no visible cause, the dropper's tip skips sideways mid-drip, the background changes abruptly, the lighting flashes once, or the liquid's meniscus warps unnaturally while the tube itself sits still; two or more such problems occur.
level_3: The test tube stays in the same place and orientation across the clip, the pig liver extract keeps a steady meniscus and fill level before the reagent is added, and the dropper approaches from one consistent direction, with no vanishing tube, bent glass, or lighting blackout; a single brief stutter in the dropper's motion or a momentary soft-focus frame during dispensing is acceptable.
level_4: The test tube stays centered and motionless, the dropper enters from the same direction each time and lines up with the tube mouth, the liquid surface stays flat and level except at the moment of mixing, and the lighting stays even across the clip; at most one small, brief mismatch is visible, such as a slight wobble in the dropper's path.
level_5: The test tube's position, tilt, and size stay identical for the entire clip; the dropper moves in one smooth, continuously slowing path down to the tube mouth; the stream of reagent falls straight and unbroken until it meets the liquid surface; the meniscus rises smoothly as liquid is added, without bouncing or oscillating; and the lighting and camera framing stay constant throughout, with no jump cuts or scale changes.