Domain: Healthcare — Pharmaceutical Chemistry
Target concept: Silver Nitrate Precipitation Test for Identification of Phenobarbital

Video generation prompt: Weigh a precise amount of phenobarbital sample into a clean test tube, add dilute sodium hydroxide solution to dissolve it, and then gradually add silver nitrate solution while gently shaking. Maintain room temperature and use standard laboratory glassware. Clearly demonstrate the sequential procedures using a pipette and test tube.

Evaluation guide:
(i) Target concept: Silver nitrate reacts with the sodium salt of phenobarbital, formed by dissolving it in dilute sodium hydroxide, to give a silver-phenobarbital precipitate; the first precipitate that forms redissolves on gentle shaking, and only after further silver nitrate is added does a permanent, non-redissolving white curdy precipitate remain, confirming the drug's identity.
Minimum mechanism: Phenobarbital's imide N-H must be ionized by the alkaline medium before Ag+ is introduced; Ag+ must directly contact the ionized drug anion to nucleate silver phenobarbital; the first-formed precipitate is metastable and dissolves under gentle agitation while excess dissolved phenobarbital anion remains in solution; once enough silver nitrate has been added, the precipitate no longer redissolves and is kinetically stabilized (curdy, non-settling) under continued gentle shaking.
(ii) Storyline: [Frame 0-2] White phenobarbital solid placed in upright test tube -> [Frame 3-4] Dilute sodium hydroxide solution added via pipette -> [Frame 5-6] Solution becomes optically homogeneous (transparent liquid) -> [Frame 7-8] Silver nitrate solution enters tube from pipette tip in small increments -> [Frame 9] A white precipitate first appears at the entry point, then thins and clears again as the tube is shaken -> [Frame 10-12] Continued dropwise addition of silver nitrate produces a white curdy precipitate that no longer clears on shaking -> [Frame 13-end] The permanent precipitate remains uniformly suspended during continuous gentle shaking; all events occur from a fixed frontal viewpoint with no occlusion or perspective shift.

Manual:
Experimental Procedure
1. Weigh phenobarbital solid and place in clean test tube.
2. Add dilute sodium hydroxide solution using a pipette; swirl gently until fully dissolved.
3. Add silver nitrate solution dropwise using a pipette while gently shaking the tube.
Observation of Experimental Phenomena
A white precipitate first forms where the silver nitrate solution enters the liquid, but it dissolves again on gentle shaking; as silver nitrate solution continues to be added dropwise, a permanent white curdy precipitate eventually forms and no longer redissolves on shaking.
Summary of Experimental Principles
In alkaline solution, phenobarbital's imide group is ionized and forms an insoluble silver salt with Ag+ ions. The initially formed precipitate redissolves because excess ionized phenobarbital remains available in solution; once enough silver nitrate has been added, a permanent white precipitate (silver phenobarbital) forms and persists, confirming the drug's identity.

Prompt Grounding rubric:
level_1: No test tube is visible; no white phenobarbital solid is shown; no pipette is present; no silver nitrate solution or its container appears; no sodium hydroxide addition step is depicted; the sequential action of adding reagent while shaking is entirely missing.
level_2: A test tube containing a white solid is present, but nothing identifies the solid as phenobarbital; a pipette appears but is never used to deliver liquid into the tube; a silver nitrate container is shown but no delivery from it occurs; a solvent container is present but no transfer of its contents into the tube is shown.
level_3: A test tube holding white phenobarbital solid is present; a dilute alkaline solution (sodium hydroxide) is visibly added to the tube using a pipette; silver nitrate solution is visibly delivered from a labeled container into the same tube; a gentle shaking motion of the tube is shown; the test tube, pipette, silver nitrate container, and solvent container are all present and correctly associated with their roles in the sequence.
level_4: Everything shown at the 3-point level is present, and in addition the pipette delivers the alkaline solvent before silver nitrate (correct order); the silver nitrate is delivered gradually, as a visible sequence of drops or a thin continuous stream, rather than all at once; shaking begins only after silver nitrate addition starts; no extraneous prop (gloves, printed labels, timers) dominates the frame or blocks the core actions from view.
level_5: Everything shown at the 4-point level is present, and in addition the white solid is clearly weighed on a balance or weighing paper and transferred into the tube before any liquid is added; the alkaline solvent fully dissolves the solid so the tube contents become a homogeneous, transparent liquid before silver nitrate is introduced; the silver nitrate stream is delivered continuously and evenly while shaking proceeds; the camera viewpoint, tube position, and pipette angle stay fixed relative to one another throughout, with no cutaways or repositioning.

Scientific and Causal Correctness rubric:
level_1: No precipitate ever forms; the solution stays clear throughout; no color change is visible; no state change from liquid to suspension occurs; there is no visible causal link between silver nitrate addition and any optical change in the tube.
level_2: A precipitate of the wrong color appears (e.g., yellow, tan, or grey rather than white); or a precipitate forms before any silver nitrate is added; or the first precipitate appears instantly upon the alkaline solvent addition alone, before silver nitrate contact; or the precipitate is coarse and crystalline/granular rather than the expected fine, curdy texture; or a white precipitate forms and then fully clears on shaking but no second, permanent precipitate ever reappears by the end of the video.
level_3: A white precipitate appears only after silver nitrate solution first contacts the dissolved phenobarbital solution; the precipitate has a soft, curdy, cloud-like texture rather than granular crystals; on continued gentle shaking this first precipitate clears or substantially redissolves, and as silver nitrate continues to be added dropwise a second white curdy precipitate reappears and persists (it does not fully redissolve again) by the end of the sequence; no non-white color deviation is visible at any point.
level_4: Building on the 3-point behavior, the first precipitate clears completely on shaking, leaving the liquid fully transparent before the second precipitate begins to form; the reappearance of the permanent second precipitate is visibly and gradually tied to how much additional silver nitrate has been added, not to an abrupt cut or an arbitrary time cue; the final precipitate shows no clumping or layering as it forms.
level_5: Building on the 4-point behavior, the precipitate is exclusively white throughout, with no off-white, grey, or yellow tint at either stage; both the clearing of the first precipitate and the formation of the second one visibly originate at the point where silver nitrate enters the liquid; the permanent precipitate's curdy texture is consistent across the visible volume; once the permanent precipitate has formed, it neither settles into a compact layer nor fades in density for the remainder of the video.

Spatiotemporal Consistency rubric:
level_1: The test tube is missing from some frames and then present again later with no visible hand placing or removing it; the pipette jumps between locations with no visible movement in between; liquid appears or disappears without a continuous motion path; an abrupt, action-unrelated lighting change occurs; the background shifts mid-sequence; the shaking motion starts or stops instantaneously with no visible acceleration or deceleration.
level_2: The test tube rotates more than roughly 30 degrees with no supporting hand visible; the pipette tip moves outside the frame during liquid delivery; the silver nitrate stream detaches from the pipette tip into floating droplets; the shaking motion is jerky, with two or more visible pauses or direction reversals; a precipitate appears before silver nitrate has entered the frame.
level_3: The test tube stays fully visible and stationary in frame throughout; the pipette keeps a consistent orientation and stays in contact with the silver nitrate container and the tube opening as it moves between them; liquid delivery follows a continuous, visible path from source to target; the shaking motion is smooth, rhythmic, and stays within a small wrist-level range; the precipitate appears only inside the tube and spreads outward gradually from where the reagent entered.
level_4: Alongside the 3-point behavior, the camera viewpoint stays fixed with no zoom, pan, tilt, or focus change; the lighting stays even, without sudden glare, new shadow edges, or brightness shifts; every object edge (tube, pipette, precipitate boundary) stays sharp and unblurred during motion; the precipitate's spread through the liquid is continuous, with no sudden jump in its extent from one moment to the next.
level_5: Alongside the 4-point behavior, motion between frames reads as fluid, with no strobing, ghosting, or motion blur that obscures the tube, pipette, or precipitate boundary; the tube and any background elements keep the same relative position during shaking with no swimming or drifting; the pipette tip stays visibly aligned with the tube opening for the whole delivery, without wandering off to the side; the precipitate's density appears to increase smoothly and evenly, with no visible flicker or sudden change in how cloudy the liquid looks.