Domain: Healthcare — Nutrition and Food Hygiene
Target concept: Determination of Arsenic in Heavy Metals

Video generation prompt: A test tube containing 10 mL of food extract with excessive arsenic ions was treated with silver nitrate-nitric acid solution, uniformly mixed, and then heated in a 50°C water bath for 10 minutes. The scene was continuously photographed for ten minutes with the camera aligned with the test tube.

Evaluation guide:
(i) Target concept: Visual confirmation of arsenic presence via a pale-yellow to yellowish-brown particulate turbidity (silver arsenite/arsenate) forming in AgNO₃-HNO₃-treated food extract under mild heating.
Minimum mechanism: Arsenite/arsenate ions must be present in the extract; Ag⁺ delivered from the silver nitrate reagent must contact these ions in the mildly acidified (dilute HNO₃) liquid; warming to ~50°C promotes nucleation and coarsening of the fine pale-yellow to yellowish-brown silver arsenite/arsenate turbidity; the reaction must not be masked by competing anions (e.g., sulfide, phosphate, chloride) that would form their own precipitates with Ag⁺ and give a misleading color/turbidity.
(ii) Storyline: [Frame 0–1] Static shot: upright test tube with clear-to-pale-yellow liquid (food extract), camera fixed and frontal. [Frame 2–3] A dropper/pipette enters frame and delivers the silver nitrate-nitric acid reagent into the tube; liquid surface briefly disturbed. [Frame 4–5] Gentle swirling produces uniform mixing; the liquid takes on a faint haze. [Frame 6–7] Tube is lowered into the 50°C water bath (visible contact with the water line); meniscus settles. [Frame 8–10] Fine pale-yellow to yellowish-brown particulates nucleate and coarsen, drifting toward the bottom, culminating in a visibly turbid pale-yellow/yellowish-brown suspension occupying roughly the lower third to half of the tube by the final frame. Fixed frontal viewpoint keeps the full tube in view; no occlusion; lighting stays constant; transitions are smooth and causally linked.

Manual:
Experimental Procedure
1. Place a clean test tube containing 10 mL of food extract on a stand.
2. Add silver nitrate-nitric acid solution dropwise; swirl gently to mix uniformly.
3. Immerse the tube in a 50°C water bath; maintain for the duration of observation.
Observation of Experimental Phenomena
A fine pale-yellow to yellowish-brown particulate turbidity develops progressively in the liquid, starting as a faint haze that coarsens and drifts toward the bottom; no gas evolution, no shift to unrelated hues (e.g., blue or green), no staining of the tube wall.
Summary of Experimental Principles
Arsenite/arsenate ions in the extract react with Ag⁺ from the silver nitrate reagent to form pale-yellow silver arsenite (Ag₃AsO₃) or yellowish-brown silver arsenate (Ag₃AsO₄). This direct precipitation is an illustrative qualitative spot test for arsenic, related to but distinct from the classic Gutzeit test (which instead reduces arsenic to arsine gas for a gas-phase indicator reaction); routine food-hygiene regulatory testing today more commonly relies on arsine-generation colorimetric methods (e.g., silver diethyldithiocarbamate) or instrumental analysis (AAS/ICP-MS).

Prompt Grounding rubric:
level_1: No test tube is visible, or no liquid extract is shown in it; the silver nitrate-nitric acid reagent is never added; no water-bath heating setup appears anywhere in the scene; the camera view is not fixed on the tube; the required setup elements (tube, extract, reagent addition, water bath) are largely absent.
level_2: A test tube or liquid appears, but core setup elements are missing: the extract is not shown as a modest partial fill, the silver nitrate-nitric acid reagent is never visibly delivered into the tube, or no water-bath heating context is shown; the camera drifts, tilts, or reframes instead of staying aligned with the tube; the sequence of steps (fill tube, add reagent, heat) is not identifiable.
level_3: A cylindrical test tube holding a transparent-to-pale-yellow liquid is clearly visible; the silver nitrate-nitric acid reagent is visibly introduced and mixed into the tube (visible liquid disturbance or interface change at the moment of addition); a water-bath heating setup (tube partly submerged in a warm-water container) is shown; the camera stays fixed and centered on the tube for the whole sequence; all four setup elements (tube, food extract, AgNO3-HNO3 reagent, water bath) are present and identifiable.
level_4: All conditions for score 3 are met, AND the mixing is shown as a uniform swirl with no streaking or unmixed layering, AND the tube stays upright and stationary throughout mixing and heating, AND the water bath reads visually as warm rather than boiling (calm surface, no vigorous bubbling or vapor bursts), AND the fixed camera keeps the entire tube length in frame without cropping or zooming.
level_5: All conditions for score 4 are met, AND the liquid fills a consistent, modest portion of the tube throughout the sequence (roughly the lower third to half of its visible length), with no unexplained volume changes, AND the reagent is delivered by a distinct dropper/pipette (not poured from a bottle) that withdraws cleanly after dispensing, AND the swirling motion visibly stops before the tube enters the water bath, AND the transition from mixing to heating is continuous with no cuts or skipped steps, AND no extraneous object enters or exits the frame during the sequence.

Scientific and Causal Correctness rubric:
level_1: No color or turbidity change appears in the liquid after the reagent is added and warmed; the extract stays clear or unchanged in shade throughout; no particulate ever forms; the outcome contradicts silver arsenite/arsenate formation (e.g., the liquid instead turns blue, green, or bright red, or forms a black precipitate).
level_2: Some change occurs but is inconsistent with the arsenite/arsenate precipitation reaction: e.g., the liquid darkens uniformly or shifts toward brown/black without ever showing the expected pale-yellow to yellowish-brown particulate cloudiness; any solid that appears is white, crystalline, or clumped rather than a fine turbid haze; the change is confined only to the top or only the bottom of the liquid without spreading; there is no visible causal link between the reagent's entry and the resulting change.
level_3: After the reagent is added and mixed, the liquid develops a fine pale-yellow to yellowish-brown particulate turbidity (not a dissolved dye); the cloudiness begins near where the reagent entered and spreads through the liquid; particles remain suspended or settle slowly rather than dropping instantly as a solid mass; no competing effects (gas bubbles, frothing, or a dissolving solid) are visible; the turbidity is consistent with silver arsenite/arsenate precipitate forming from Ag⁺ reacting with arsenite/arsenate ions.
level_4: All conditions for score 3 are met, AND the pale-yellow to yellowish-brown turbidity stays within the liquid with no coating or staining on the tube wall, AND the cloudiness thickens gradually over the heating period rather than jumping instantly to full turbidity, AND no unrelated hues appear (e.g., no blue, deep green, or purple tint suggesting a different metal ion), AND the liquid does not stay suspiciously clear for more than about 5 seconds after mixing when turbidity should be developing.
level_5: All conditions for score 4 are met, AND the particulates appear as a fine, evenly dispersed haze rather than clumped flakes or a single solid mass, AND the turbidity visibly increases in density from the start to the end of the heating period, AND at no point does the suspension clear, fade, or redissolve back to a transparent liquid, AND the tube wall, meniscus, and air-liquid interface stay free of discoloration, with the pale-yellow/yellowish-brown turbidity persisting through the final frame.

Spatiotemporal Consistency rubric:
level_1: The test tube's position, size, or tilt jumps abruptly between frames instead of moving continuously; the tube or its liquid blinks out of view for a frame and returns with a different fill level or color than before; the liquid surface snaps to a new height with no visible pouring or draining motion; the water bath, pipette, or backdrop swap out or vanish without explanation.
level_2: The tube rocks or tips by a large, unrealistic angle (well beyond roughly 15° off vertical) during mixing or heating; the liquid surface behaves out of step with the visible action (e.g., it stays perfectly flat while the pipette is actively dispensing, or churns while the tube sits untouched); room brightness or the shadow cast by the tube on the bench shifts position independent of any camera or object movement; background props (stand, water-bath container) flicker or change shape between frames.
level_3: The tube shows only a slight sway of a few degrees (under about 5°) while being handled or lowered into the water bath, correcting itself within roughly a second; the liquid meniscus shows a brief, minor distortion right as the reagent drop lands, then settles; the tube's position, the water bath, and the camera framing stay consistent, with no jump cuts, no tube swapping, and no sudden reframing.
level_4: All conditions for score 3 are met, AND the tube holds a single vertical orientation for the entire sequence with no drift or rotation (tilt staying within roughly ±5°), AND the liquid meniscus curvature and any ripples move in a way that matches the reagent drop and swirl, not appearing on their own or lingering after the motion stops, AND the light source and the shadow it casts on the tube and bench stay fixed in direction and brightness throughout, AND the tube's outline and position stay aligned frame to frame with no drifting scale or sideways creep.
level_5: All conditions for score 4 are met, AND the pipette's entry and withdrawal move at a steady, continuous pace with no sudden speed changes, AND the swirl imparted during mixing rotates smoothly without stalling or skipping, AND the water bath shows only the mild, steady visual cues expected at 50°C (gentle warmth, no vigorous boiling or vapor bursts), AND the tube, stand, and water bath keep the same relative arrangement and scale from the first frame to the last, consistent with a single steady camera filming a stationary setup.