Domain: Healthcare — Pharmaceutical Chemistry
Target concept: Sodium Aminosalicylate Assay

Video generation prompt: An appropriate amount of sodium p-aminosalicylate was placed in a test tube. Dilute hydrochloric acid and sodium nitrite were added, followed by alkaline β-naphthol. The scene was continuously photographed for about ten seconds.

Evaluation guide:
(i) Target concept: Azo dye coupling reaction via diazotization of aromatic amine
Minimum mechanism: Presence of primary aromatic amine group (–NH₂) on para position of salicylic acid derivative; acidic environment enabling nitrous acid generation; electrophilic diazonium ion formation; nucleophilic coupling at β-position of naphthol under alkaline conditions yielding insoluble azo pigment.
(ii)Storyline: Frame 0–1: Static shot of test tube with white crystalline solid. Frame 2–3: Dropper introduces clear liquid (HCl) into tube: no color change. Frame 4–5: Second dropper introduces clear liquid (NaNO₂): still no color change. Frame 6–7: Third dropper introduces a colorless-to-pale alkaline β-naphthol solution: the liquid itself carries no red tint as it enters the tube; red speckling first appears only where it actually contacts and mixes with the diazonium-salt solution already present. Frame 8–10: Red particles grow, settle, and uniformly distribute as brick-red precipitate; no dissolution or color shift. Viewpoint: Fixed frontal close-up, shallow depth of field emphasizing tube interior; all reagents and reactions fully visible without occlusion.

Manual:
Experimental Procedure
1. Place a small amount of white crystalline sodium p-aminosalicylate into a clean test tube.
2. Add dilute hydrochloric acid dropwise.
3. Add sodium nitrite solution dropwise.
4. Add alkaline β-naphthol solution dropwise.
Observation of Experimental Phenomena
A brick-red precipitate forms immediately after addition of alkaline β-naphthol and remains stable.
Summary of Experimental Principles
Sodium p-aminosalicylate undergoes diazotization in acidic medium with nitrous acid (from NaNO₂ + HCl), forming a diazonium salt; this couples with alkaline β-naphthol to yield a brick-red azo dye precipitate.

Prompt Grounding rubric:
level_1: No test tube is visible in frame; no white crystalline sodium p-aminosalicylate solid is shown; none of the three reagents (dilute HCl, sodium nitrite solution, alkaline β-naphthol solution) appear as separate droppers or containers; the three-step addition sequence is not depicted at all.
level_2: A test tube holding a white or off-white solid is shown, but the solid's form is wrong for sodium p-aminosalicylate (e.g., shown as coarse granules or a liquid rather than fine crystalline powder); at least one of the three reagents is missing, unlabeled, or shown in the wrong physical state (e.g., alkaline β-naphthol shown as a solid); the three additions are shown but out of the correct order (e.g., alkaline β-naphthol added before sodium nitrite).
level_3: Test tube contains a white crystalline solid consistent with sodium p-aminosalicylate; three distinguishable reagent sources are shown in correct order: dilute HCl (clear liquid) added first, sodium nitrite solution (clear liquid) added second, and alkaline β-naphthol solution (colorless-to-pale, not orange-red) added third, each with a visible, separate contact event with the tube's contents.
level_4: All conditions of score 3 are met; each reagent keeps a consistent liquid form and dropper/vial container across its entire appearance; no unrelated objects (hands, on-screen text, stray labels) obscure the test tube or reagent droppers; the test tube stays centered and upright in the same position throughout the sequence.
level_5: All conditions of score 4 are met; the three reagent droppers/vials stay visually distinct from one another by shape alone, since HCl, sodium nitrite solution, and alkaline β-naphthol solution are all correctly shown as colorless-to-pale liquids with none tinted red before use; each addition shows a clear droplet or stream entering the tube mouth with no splashing outside the tube; the test tube, reagents, and their spatial arrangement remain identifiable as the same objects in every frame.

Scientific and Causal Correctness rubric:
level_1: The mixture stays white, colorless, or unchanged through the entire sequence; no red precipitate or suspension ever forms; nothing on screen indicates a diazotization or coupling reaction took place.
level_2: A color change happens, but it is chemically wrong for this reaction: for example the mixture turns purple, blue, black, or yellow instead of brick-red, or a red tint appears before the alkaline β-naphthol is added, or any red color fades away within about a second of appearing.
level_3: A brick-red precipitate appears only after the alkaline β-naphthol is added, with no color change during the earlier HCl or sodium nitrite additions; the red material looks like distinct particles or speckles rather than a uniform tint dissolved in the liquid, and it reads as true brick-red rather than pink, orange, or brown.
level_4: All conditions of score 3 are met; once it appears, the brick-red precipitate persists continuously rather than flickering in and out; the sodium nitrite step shows no premature red or orange coloring that would falsely suggest the diazonium salt itself is colored; the red particles keep the same hue and grain size rather than dissolving, greying, or blackening afterward.
level_5: All conditions of score 4 are met; the brick-red precipitate visibly concentrates and settles toward the bottom of the test tube rather than staying evenly suspended; the red color's intensity keeps increasing rather than flickering up and down after the alkaline β-naphthol addition; the red particles stay separable to the eye rather than smearing into a uniform haze or clumping into a few large lumps.

Spatiotemporal Consistency rubric:
level_1: The test tube vanishes from view and then reappears, or reagents materialize inside the tube with no dropper motion bringing them in; the room lighting jumps abruptly between bright and dark from one moment to the next; there is a visible camera cut or angle jump partway through the sequence; the tube tilts or spins with no dropper or hand action causing it.
level_2: The test tube stays visible but slides sideways by more than about a quarter of its width between reagent additions; the three droppers enter the frame from different, inconsistent directions (e.g., left for HCl, top for sodium nitrite, right for alkaline β-naphthol); the shadow cast by the tube jumps to a new position instead of shifting gradually; the background surface behind the tube warps or stretches.
level_3: The test tube stays fixed near the center of the frame with the same upright orientation throughout (no rotating, tilting, or sliding); every dropper enters from the same general direction relative to the tube across all three additions; the overall lighting stays even, without sudden bright flares turning on or off; the background stays static and uncluttered.
level_4: All conditions of score 3 are met; each dropper's tip moves smoothly into and out of frame without jerking or freezing; the liquid stream leaving each dropper keeps a steady thickness and path as it falls; the tube wall and liquid surface look continuous frame to frame with no sudden flicker; a droplet never appears inside the tube before its dropper tip has actually reached the tube mouth.
level_5: All conditions of score 4 are met; the dropper tip consistently overlaps the near rim of the tube the same way whenever it is in position, showing believable depth; no motion blur hides the shape of a falling droplet or the forming red particles; the test tube and reagents keep a constant apparent size with no unexplained zooming or perspective shift; the tube outline and liquid surface show no visible jitter or drift across the sequence.