Domain: Healthcare — Pharmaceutical Chemistry
Target concept: Procaine Assay

Video generation prompt: An appropriate amount of procaine sample is placed in a dry test tube. An appropriate amount of dilute hydrochloric acid is added to dissolve the sample, followed by the addition of sodium nitrite solution and thorough shaking. Finally, alkaline β-naphthol reagent is added, and the mixture is gently shaken.

Evaluation guide:
(i) Target concept: Azo dye coupling reaction confirming primary aromatic amine functionality in procaine.
Minimum mechanism: Diazotization must precede coupling; nitrous acid must be generated *in situ* from acidic NaNO₂; coupling requires alkaline pH and β-naphthol specifically; red precipitate must be insoluble azo dye, not soluble dye or oxidation product.
(ii)Storyline: Frame opens on dry test tube → solid procaine placed inside → dilute HCl poured in, dissolving solid uniformly → NaNO₂ solution poured in, no visible change → alkaline β-naphthol poured in → immediate localized red floc formation → gentle shaking disperses then settles red precipitate. All events occur in fixed frontal view; reagents must enter frame from consistent off-screen position; precipitate must originate *within* liquid phase, not adhere to tube wall first; no intermediate states (e.g., orange/yellow) allowed before red precipitate.

Manual:
Experimental Procedure
1. Place solid procaine sample into a dry test tube.
2. Add dilute hydrochloric acid and shake until sample dissolves completely.
3. Add sodium nitrite solution and shake thoroughly.
4. Add alkaline β-naphthol reagent and shake gently.
Observation of Experimental Phenomena
A red precipitate forms only after addition of alkaline β-naphthol reagent.
Summary of Experimental Principles
Procaine undergoes diazotization with nitrous acid (generated in situ from NaNO₂ + HCl), followed by coupling with alkaline β-naphthol to form a red azo dye precipitate — a confirmatory test for primary aromatic amines.

Prompt Grounding rubric:
level_1: None of the required materials are shown: no test tube, no solid procaine sample, and none of dilute hydrochloric acid, sodium nitrite solution, or alkaline β-naphthol reagent is depicted; the video shows no version of this procedure being carried out.
level_2: A test tube or a reagent container appears, but the three reagents (dilute HCl, sodium nitrite solution, alkaline β-naphthol) are not clearly shown as distinct liquids added in any recognizable order, and the procaine sample itself is never shown going into the tube.
level_3: The test tube, the solid procaine sample placed inside it, dilute hydrochloric acid added onto the sample, and sodium nitrite solution added afterward are all clearly shown in that order; however the alkaline β-naphthol addition is missing entirely or is shown before the sodium nitrite step.
level_4: All five elements appear and are used in the posted-prompt order: solid procaine placed in a dry test tube, dilute hydrochloric acid added and mixed in, sodium nitrite solution added and shaken, and finally alkaline β-naphthol reagent added and gently shaken; no reagent is swapped for another (no plain water standing in for the acid, no plain phenol standing in for β-naphthol), and no extra steps are inserted.
level_5: Everything required for 4-level fidelity is present, and in addition every object keeps a consistent identity across the clip: the same test tube is used throughout with no cut to a different one, the procaine sample is visibly solid/granular before the acid is added, each reagent container looks the same every time it appears, and the four steps play out as one continuous shot (or cleanly matched cuts) from a single, unchanging camera angle.

Scientific and Causal Correctness rubric:
level_1: No color or precipitate change happens at any point in the clip: the liquid stays clear and colorless even after the β-naphthol reagent is added, showing no sign that a diazotization/coupling reaction ever occurred.
level_2: A color or precipitate change happens, but at the wrong step or with the wrong color: e.g., red color appears as soon as the acid is added (before diazotization is even possible), the color that forms is blue or purple instead of red, or a precipitate appears without the β-naphthol ever being added.
level_3: The procaine sample dissolves fully and cleanly in the dilute hydrochloric acid with no leftover solid; adding the sodium nitrite solution produces no visible change (no bubbling, no color, no cloudiness); only once the alkaline β-naphthol reagent goes in does a red, particulate (not just tinted) precipitate appear.
level_4: Everything at the 3-level is shown clearly and additionally the dissolution step looks visually complete (no floating or gritty undissolved solid before the nitrite is added), the sodium nitrite addition truly shows no visible effect of any kind, and the red precipitate that eventually forms stays as a distinct solid phase rather than a diffuse red tint dissolved in the liquid.
level_5: Everything at the 4-level is shown, and the red precipitate additionally has the right texture for this reaction (coarse or flocculent clumps rather than a fine colloidal haze or a surface film), and it visibly settles once shaking stops, with no extra yellow/brown byproduct color or cloudiness from any step that would suggest a side reaction.

Spatiotemporal Consistency rubric:
level_1: The test tube or a reagent bottle vanishes from the frame and reappears somewhere else, the camera cuts abruptly to a different lighting setup mid-procedure, or the tube's orientation snaps by more than 90 degrees between one frame and the next with no visible hand or camera motion causing it.
level_2: An object (tube or bottle) blinks out of view for part of a frame and comes back, a poured liquid stream freezes mid-air and then resumes, the shaking motion has obvious unnatural pauses, or the tube's tilt changes by more than 45 degrees without a smooth in-between motion.
level_3: The test tube stays centered with the reagent bottles beside it, pours look like one continuous stream from bottle to tube, and shaking looks like one continuous motion, but there is one small blemish, such as a reagent bottle's shadow briefly pointing a different way for a moment, or the tube's outline looking slightly soft for a frame or two, without affecting the viewer's ability to follow the procedure.
level_4: The camera holds one fixed framing for the whole clip with no pan, tilt, or zoom; the test tube stays in the same position and orientation throughout; every reagent is poured in from the same side of the frame each time; and the shaking motion repeats with a consistent tempo and arc from one shake to the next.
level_5: The whole sequence reads as one uninterrupted, steady shot: the tube and bottles hold their exact positions and shapes from start to finish, the liquid's meniscus deforms naturally while pouring and settles smoothly afterward, the red precipitate builds up gradually rather than snapping instantly to full opacity, and there is no visible stutter, skipped frame, or shake in the footage at normal playback speed.