Domain: Natural Science — Chemistry
Target concept: Arsenic Ion Detection in Realgar (Silver Nitrate Colorimetric Method)

Video generation prompt: Place the realgar powder in a beaker, add dilute nitric acid, and warm gently to dissolve it, filter and take the filtrate, then add 2 drops of silver nitrate solution.

Evaluation guide:
(i) Target concept: Colorimetric detection of As³⁺ via AgNO₃-induced precipitation
Minimum mechanism: Realgar (As₄S₄) resists dilute hydrochloric acid but is oxidized and dissolved by warm dilute nitric acid, which converts the sulfide sulfur toward elemental sulfur while releasing arsenic mainly as soluble As³⁺; the filtrate must be particle-free (any residual sulfur removed by filtration) to isolate the soluble arsenic species; Ag⁺ must be introduced to form insoluble yellow silver arsenite (Ag₃AsO₃); no interference from sulfides (which would give a black precipitate) or phosphates (which also give a yellow precipitate but require a different pH)
(ii)Storyline: [Phase 1: Setup] Beaker containing orange-red realgar powder is stationary in frame. [Phase 2: Acid dissolution] Dilute nitric acid is poured over the realgar with gentle warming; liquid level rises and the powder gradually breaks down and disperses. [Phase 3: Filtration] Mixture transfers through funnel/filter paper into a new container; the filtrate appears optically clear (no haze, no particles). [Phase 4: Detection] Silver nitrate dropper approaches the filtrate; two discrete drops detach, fall vertically, contact the surface, and trigger localized yellow precipitate formation that persists. [Visibility constraints] All critical zones (beaker interior, filter paper interface, filtrate surface) remain fully in view and in focus; no camera cuts or zooms that obscure causality; viewpoint remains fixed frontal-midlevel to capture object relationships and precipitate emergence.

Manual:
Experimental Procedure
1. Place realgar powder in a clean beaker.
2. Add dilute nitric acid and warm gently to dissolve the realgar.
3. Filter the mixture and collect the clear filtrate in a separate container.
4. Add exactly 2 drops of silver nitrate solution to the filtrate.
Observation of Experimental Phenomena
A distinct yellow precipitate forms immediately upon addition of silver nitrate to the clear filtrate.
Summary of Experimental Principles
Warm dilute nitric acid oxidizes and dissolves realgar, releasing arsenic ions (As³⁺) into solution; these react with Ag⁺ ions to form insoluble yellow silver arsenite (Ag₃AsO₃), confirming arsenic presence via colorimetric detection.

Prompt Grounding rubric:
level_1: No realgar powder, no beaker, no dilute nitric acid, no filtration apparatus (funnel/filter paper), no filtrate collection, and no silver nitrate solution appear anywhere in the video; or the scene is unrelated to this chemistry setup entirely.
level_2: At least one correct object is present (e.g., the beaker or the silver nitrate dropper bottle), but none of the five procedural steps are shown: realgar is never placed in the beaker, nitric acid is never added, the mixture is never warmed, no filtration takes place, and silver nitrate is never dispensed into a filtrate.
level_3: Realgar powder is placed in the beaker AND dilute nitric acid is visibly added AND the mixture is visibly warmed (e.g., held over a flame or hot plate, or shown with a gentle heat cue such as rising steam) AND a filtration step is shown (funnel, filter paper, and receiving container) AND the filtrate is collected in a clear container AND 2 drops of silver nitrate solution are added to that filtrate; all objects and actions are depicted, but at least one lacks visual confirmation of completion (e.g., acid poured but no liquid-level change in the beaker; the beaker is never shown being warmed; filtration shown but no liquid visibly passing through the paper; the dropper is held over the filtrate but no drop is seen detaching).
level_4: All six procedural elements are fully and unambiguously depicted in order: (1) realgar powder placed in the beaker, (2) dilute nitric acid added with a visible pour/stream into the beaker, (3) the mixture is visibly warmed (e.g., over a flame or hot plate, with a visible heat cue), (4) filtration performed with liquid visibly passing from the funnel into the filtrate container, (5) the filtrate is clearly a transparent liquid in a separate container, (6) silver nitrate solution is dispensed as two distinct drops into that filtrate; no missing objects, no mislabeled reagents (e.g., no sulfuric acid bottle standing in for nitric acid, no sodium chloride solution standing in for silver nitrate).
level_5: All conditions above are met, and spatial continuity holds throughout: the same beaker holds the realgar, acid, and warming step before filtration; the filtrate container is a physically distinct vessel positioned next to the filtration setup; the silver nitrate dropper is held directly above the filtrate container while dispensing; the beaker, funnel, and dropper keep consistent size, transparency, and material appearance across the video; the filtrate is never shown appearing suddenly without the preceding warming and filtration steps.

Scientific and Causal Correctness rubric:
level_1: No color change occurs after silver nitrate is added; or the color produced contradicts arsenic detection (e.g., a black precipitate typical of sulfide, or a green solution); or any precipitate forms in the filtrate before silver nitrate is added; or the filtrate is already turbid before the AgNO₃ drops arrive.
level_2: The filtrate is transparent before AgNO₃ addition, but afterward there is either no visible change, only uniform cloudiness with no distinct particles, or a precipitate in the wrong color (white, blue, red) or wrong physical form (gel, film, or gas bubbles).
level_3: The filtrate is transparent before AgNO₃ addition, and after the two drops are added a yellow precipitate appears and either stays suspended or settles, but the yellow is ambiguous (e.g., a pale cream barely distinguishable from off-white), or the precipitate appears before the second drop has finished contacting the filtrate, or it is not clearly localized at the drop's point of contact.
level_4: The filtrate is transparent before AgNO₃ addition, and after both drops fully contact it a clearly yellow precipitate forms only within the filtrate, stays visually distinct from the container and background, appears only after both drops have made contact (no precipitate forming ahead of drop arrival), and no competing effects (bubbling, haze, unexplained color diffusion) appear.
level_5: Everything above holds, and the causal chain is unmistakable: the yellow precipitate appears only where the AgNO₃ drops land, spreads outward continuously from that point, keeps a granular rather than smeared texture, and does not redissolve or disperse for the rest of the video; there is no yellow tint traceable to lighting, reflections, or a dirty container; the precipitate reads as silver arsenite (Ag₃AsO₃) rather than a different yellow solid (no cadmium or lead reagents are present that could form cadmium yellow or lead chromate instead).

Spatiotemporal Consistency rubric:
level_1: The beaker or filtrate container jumps to a new position or size between shots; the beaker appears to shatter and then reform intact; the room lighting switches brightness or direction with no visible cause; or the pouring/filtration motion freezes while liquid keeps visibly flowing.
level_2: A major discontinuity breaks the action: the filtration stream is shown as a static frame with no liquid actually moving through the funnel; the silver nitrate dropper appears already extended over the filtrate with no visible approach; the beaker switches from tilted to upright with no hand or arm motion causing it; or the filtrate container is shown empty and then full with no pouring in between.
level_3: The beaker, funnel, filtrate container, and dropper stay in the same relative arrangement throughout, and the acid pour and dropper's descent both follow one continuous, unbroken path, but a minor flaw is visible, such as a brief flicker as the scene shifts from dissolution to filtration, a short blur on the dropper tip during dispensing, or a small jump when the filtrate container is set down.
level_4: No object jumps position, the beaker rim and funnel keep their round, undistorted shape throughout, and the room lighting stays at one brightness and direction across the whole sequence; the acid stream falls smoothly with no floating droplets or reversed flow; the only imperfection is something small and non-core, such as a faint soft edge on the filter paper or a barely visible flicker as a drop separates from the dropper tip.
level_5: Everything above holds, and continuity is essentially seamless: the filtration stream flows in one unbroken line from funnel to filtrate container; each silver nitrate drop detaches as a clean rounded bead, holds its shape while falling, and merges into the filtrate without splashing or bouncing back; no repeated or stuttering motion appears, and the beaker, funnel, and dropper keep consistent parallax with the background throughout.