Domain: Engineering — Food and Bioprocess Engineering
Target concept: Determination of Zinc in Food by the Dithizone Spectrophotometric Method

Video generation prompt: Place 2 mL of oyster extract into a test tube, add the dithizone solution and acetate buffer, and shake thoroughly to mix.

Evaluation guide:
(i) Target concept: Visual confirmation of Zn²⁺ presence via dithizone chelation colorimetry, using a water-dispersible dithizone reagent read directly in the aqueous phase.
Minimum mechanism: A water-dispersible dithizone reagent (dithizone pre-dissolved in a surfactant-stabilized aqueous carrier, rather than the classical organic-solvent form used for CCl4/chloroform extraction) must be present in its active form; acetate buffer must provide pH control (~pH 4.5–5.5) to enable selective Zn²⁺ binding over Cd²⁺/Pb²⁺; mechanical agitation must ensure complete complex formation and homogenization within the single aqueous phase.
(ii)Storyline: Frame 1–2: Static shot of test tube with 2 mL oyster extract (pale yellow-brown liquid). Frame 3–4: Dithizone reagent (red-purple) added from separate container, with visible droplets entering tube. Frame 5–6: Acetate buffer (colorless) added: meniscus rises. Frame 7–10: Hand grips tube and performs continuous shaking motion: liquid swirls, interfaces break, color transitions from heterogeneous to homogeneous red-purple within the single aqueous phase. Perspective: Fixed frontal close-up, full test tube in frame, no occlusion, consistent lighting, top-to-bottom visibility of liquid column throughout.

Manual:
Experimental Procedure
1. Place 2 mL oyster extract into a clean test tube.
2. Add the water-dispersible dithizone reagent dropwise (dithizone pre-dissolved in a surfactant-stabilized aqueous carrier, rather than the classical chloroform/CCl4 extraction solvent).
3. Add acetate buffer solution.
4. Cap and shake thoroughly to mix.
Observation of Experimental Phenomena
Oyster extract (pale yellow-brown) + dithizone reagent (red-purple) + acetate buffer (colorless) form a visibly layered, non-uniform mixture before shaking; after shaking, a homogeneous red-purple color develops throughout the single aqueous phase — indicating Zn²⁺-dithizone chelate formation.
Summary of Experimental Principles
Dithizone selectively binds Zn²⁺ under weakly acidic conditions (acetate buffer, pH ~4.5–5.5) to form a red-purple chelate. In the classical method this chelate is extracted into an organic solvent (e.g., chloroform or CCl4) because dithizone itself is poorly water-soluble; here, a water-dispersible dithizone formulation is used instead, so the red-purple color develops and is read directly within the single aqueous phase rather than requiring a solvent-extraction step.

Prompt Grounding rubric:
level_1: No test tube, oyster extract, dithizone reagent, or acetate buffer appears in the video; or the wrong containers/liquids are shown (e.g., a beaker instead of a test tube, or plain water instead of oyster extract).
level_2: At least one of the required items appears (for instance, a test tube), but one or more of the others is missing: no oyster extract, no dithizone reagent, or no acetate buffer; or all the liquids are shown already mixed together with no visible pouring or adding step; or the shaking happens before the reagents are added.
level_3: A test tube holding pale yellow-brown oyster extract is shown; a red-purple dithizone reagent and a colorless acetate buffer are each added to it in turn: dithizone first, then buffer; both additions happen before any shaking starts; the tube stays in place while the liquids are added.
level_4: Everything at the 3-point level still holds, and further: the tube is picked up and visibly shaken with a clear back-and-forth or circular motion after both additions and before any color change appears; nothing in the tube or the shaking hand disappears or pops in and out of frame; the tube stays fully visible for the whole sequence.
level_5: Everything at the 4-point level still holds, and further: the tube keeps the same position and angle across the whole clip except during the shaking itself; the dithizone reagent and the acetate buffer clearly come from two separate containers (e.g., a dropper bottle for the dithizone, a different bottle or pipette for the buffer); both liquids land inside the tube with no spill over the rim; the shaking motion is one continuous, unbroken action confined to the tube, with no jump cut or flicker.

Scientific and Causal Correctness rubric:
level_1: The mixture's color never changes throughout the clip; or the final liquid ends up colorless, blue, green, yellow, or brown instead of red-purple; or a color shift happens before the reagents are added or without any shaking taking place.
level_2: A color change happens, but the final color isn't the red-purple expected of a Zn-dithizone complex: it reads instead as plain pink, orange, or violet; or the shift occurs before shaking, or while reagents are still being added rather than after mixing; or the color is a uniform wrong hue with no visible contrast between the pre-shake and post-shake states.
level_3: Before shaking, the liquid looks visibly non-uniform: the pale yellow-brown oyster extract, red-purple dithizone reagent, and colorless buffer are not yet blended together; after shaking, the whole liquid turns a uniform red-purple; this color change only becomes visible once shaking begins, and it stays until the clip ends.
level_4: Everything at the 3-point level still holds, and further: the red-purple color is confined to the liquid itself, with no red-purple residue clinging to the tube walls above the liquid line; the liquid stays clear rather than turning cloudy or opaque; the red-purple intensity looks even across the whole visible column of liquid.
level_5: Everything at the 4-point level still holds, and further: no red-purple tint appears at all until shaking starts; the color keeps deepening while shaking continues and settles into its final shade only once shaking stops; there's no fading, streaking, or gradient left behind as it settles; the final hue reads clearly as red-purple rather than a duller or different shade, consistent with the Zn-dithizone chelate described in the manual.

Spatiotemporal Consistency rubric:
level_1: The test tube is missing from view at some points in the clip and shows up again in a different spot; liquid appears to spurt out and vanish instantly; a hand enters, adds a reagent, and leaves, but the tube's position or angle has shifted from before; the shot cuts between clearly mismatched lighting or camera angles.
level_2: The test tube jumps sideways or up/down between the dithizone and buffer additions; the liquid level changes with no visible cause right after an addition; the shadow on the tube switches sides abruptly; the lighting color or brightness shifts noticeably partway through with no explanation.
level_3: The test tube stays visible in the same spot and orientation for the whole clip; the liquid level rises visibly and correctly after each addition (first dithizone, then buffer); the liquid surface rises smoothly rather than jumping; the hand that adds each reagent enters, does its job, and leaves without ever fully hiding the tube.
level_4: Everything at the 3-point level still holds, and further: the shaking motion is smooth and continuous, without freezing mid-motion or speeding up unnaturally; the liquid sloshes the way real liquid would as the hand accelerates and decelerates; the hand never appears to pass through the tube wall.
level_5: Everything at the 4-point level still holds, and further: the shadow the tube casts stays anchored to its base rather than sliding independently; the reflection on the liquid's surface moves in step with the shaking rather than lagging or leading it; the tube and the background behind it don't drift relative to each other as if the camera had moved; every motion in the clip looks like it obeys gravity and momentum, with nothing floating or snapping to a stop unnaturally.