Domain: Healthcare — Nutrition and Food Hygiene
Target concept: Sulfur Dioxide Determination (Pararosaniline Hydrochloride Method)

Video generation prompt: A test tube containing 10 mL of the sample solution with sulfur dioxide was treated with hydrochloric acid and pararosaniline hydrochloride (acid-bleached) reagent, then gently mixed and allowed to react.

Evaluation guide:
(i) Target concept: Chromogenic detection of sulfur dioxide via acid-catalyzed reaction with acid-bleached pararosaniline hydrochloride to form a stable reddish-pink chromophore (pararosaniline methylsulfonic acid).
Minimum mechanism: Acid must be present before or together with the pararosaniline hydrochloride reagent so the dye stays in its bleached, colorless form until it reacts with sulfur dioxide; mixing brings the sulfur dioxide and the reagent into contact; standing afterward gives the addition/conjugation reaction time to complete, producing the visible reddish-pink product with peak absorbance near 550 nm.
(ii)Storyline: [Frame 0–2] Static shot of upright test tube with clear liquid → [Frame 3–4] Hydrochloric acid dispensed into tube → [Frame 5–6] Pararosaniline hydrochloride reagent dispensed into same tube → [Frame 7–8] Tube gently swirled (liquid rotates cohesively, no splashing) → [Frame 9–10] Tube returns to full stillness; reddish-pink hue emerges uniformly across liquid volume and remains stable. Viewpoint: fixed frontal close-up, full tube height visible, no hand/tool occlusion after dispensing, consistent illumination from upper front quadrant.

Manual:
Experimental Procedure
1. Place a test tube containing 10 mL of sample solution.
2. Add hydrochloric acid, then the acid-bleached pararosaniline hydrochloride reagent.
3. Gently mix by swirling.
4. Let stand still to allow color development.
Observation of Experimental Phenomena
Reddish-pink color appears in the solution after mixing and persists during stillness.
Summary of Experimental Principles
Sulfur dioxide reacts with the acid-bleached pararosaniline hydrochloride reagent, added directly (not formed in situ), to yield a stable reddish-pink chromophore — the basis of the pararosaniline method.

Prompt Grounding rubric:
level_1: No test tube is visible; no sample solution is shown in it; neither the hydrochloric acid nor the pararosaniline hydrochloride (acid-bleached) reagent appears at any point; no mixing action is depicted; no stillness/reaction period follows an addition.
level_2: A test tube holding liquid is present, but the fill level does not read as roughly 10 mL; either the hydrochloric acid or the pararosaniline hydrochloride reagent is missing from the depicted additions, or a mixing motion is applied without one of the two reagents having been added; no stillness period follows the mixing.
level_3: A single test tube containing a clear liquid is shown; both the hydrochloric acid and the pararosaniline hydrochloride reagent are visibly dispensed into the tube; a gentle mixing motion (e.g., a wrist-rotating swirl) follows; the tube then sits stationary for an observable stretch of time.
level_4: All elements of 3-score are present AND: the tube stands upright and steady on a surface throughout; the two reagents are added in the correct order (hydrochloric acid first, then the pararosaniline hydrochloride reagent) as two visually distinct dispensing actions; the swirl happens only once, right after the second reagent goes in; no extraneous items (e.g., a dropper left resting in the tube, a hand or glove blocking the view of the liquid) remain in frame.
level_5: All elements of 4-score are present AND: only the one test tube appears in frame for the entire clip, with no second tube, bottle, or label sharing the shot; each dispensing action shows a clearly visible stream or series of droplets entering the tube, so the acid addition and the pararosaniline addition read as two distinct, unambiguous events; the liquid volume inside the tube visibly stays close to the 10 mL starting fill (no extra liquid added or removed) from the first reagent addition through the end of mixing.

Scientific and Causal Correctness rubric:
level_1: No color change happens at all; the liquid stays colorless, or takes on a hue that has nothing to do with this reaction (e.g., blue, green, yellow), for the entire clip; no reddish-pink tint ever appears; the solution stays a clear liquid throughout, with no precipitate, cloudiness, or separation into layers.
level_2: Some color change occurs, but the hue is wrong for the SO2–pararosaniline reaction (e.g., the liquid turns purple, orange, or brown instead of reddish-pink); or a tint appears as soon as the hydrochloric acid is added, before the pararosaniline hydrochloride reagent has entered the tube (not possible chemically, since the reagent is required to form the color); or the tint spreads across the whole frame rather than staying confined to the liquid inside the tube.
level_3: A reddish-pink color develops in the liquid after both the acid and the pararosaniline hydrochloride reagent have been added and mixed, appearing during the stillness that follows; the color stays confined to the solution inside the tube; no precipitate, bubbling, or loss of clarity accompanies it; the color is still present in the final frame of the clip.
level_4: All elements of 3-score are present AND: the reddish-pink tint only becomes visible after mixing is finished, not while either reagent is still being poured in; the color looks even in strength from the top of the liquid column to the bottom, without a darker band, streaking, or pooling in one spot; no unrelated visual effect (e.g., bubbles, a distorted meniscus) appears at the same moment the color does.
level_5: All elements of 4-score are present AND: reddish-pink is the only chemically meaningful color present: no secondary cast such as an orange edge or violet core competes with it; the tint becomes visible across the whole liquid volume at essentially the same moment rather than spreading outward from one point like a wavefront; the reddish-pink shade matches what the actual pararosaniline–SO2 reaction product looks like, rather than reading as a washed-out or oversaturated stand-in for it.

Spatiotemporal Consistency rubric:
level_1: The test tube itself vanishes from view and then reappears elsewhere in the clip, or the liquid's fill level jumps to a different height between consecutive frames with no pour shown causing it; the swirling motion skips between disconnected poses instead of flowing; the lighting flips from bright to dim (or dim to bright) partway through; the tube's tilt changes by more than roughly 15 degrees with nothing visible (no hand, no bump) causing that change.
level_2: The tube stays on screen the whole time but drifts sideways or up/down by more than its own width from where it started; the swirl looks stepped or stop-motion rather than continuous; the reddish-pink tint that has started to appear flickers between visible and colorless, or fully fades out and comes back, instead of forming once and staying; the shadow the tube casts on the tabletop swings from directly behind the tube (away from the camera, as the upper-front light dictates) to noticeably off to one side or in front of the tube, even though nothing in the shot suggests the light source has moved from its fixed upper-front position.
level_3: The tube holds one fixed position and tilt for the whole clip; the liquid surface stays continuous during the stillness phase, with no sudden jump or gap in fill level; the swirl reads as one continuous gesture rather than a series of disconnected poses; the tube's shadow stays cast directly behind the tube on the tabletop, extending away from the camera the whole time (matching light arriving from the upper-front direction described for this scene), with the same length and angle from the first frame to the last; no unrelated object enters or leaves the frame partway through.
level_4: All elements of 3-score are present AND: the tube does not appear to shift in depth relative to the background behind it, consistent with a static camera; the tube's cylindrical outline and the curve of the liquid's surface keep a steady, undistorted shape rather than warping between frames; the liquid and the tube's glass never appear to jump between a noticeably brighter frame and a noticeably darker one: brightness stays within roughly a 10% range from one frame to the next, consistent with the same unmoving upper-front light source lighting the whole clip; the tube holds its exact resting spot on the surface throughout, without a slow creeping drift.
level_5: All elements of 4-score are present AND: the tube keeps the same visible spacing and angle to a fixed background reference (e.g., a countertop edge or the frame's border) across the entire clip; the meniscus curve and the highlight on the liquid's surface stay geometrically consistent with the tube's fixed shape and the fixed light source throughout; the swirling motion moves at a steady, even pace with no sudden speed-up or slow-down; the motion never appears to stutter or repeat as if a frame had been duplicated.