Domain: Natural Science — Chemistry
Target concept: Aluminum Sulfate Determination (Barium Chloride Colorimetric Method)

Video generation prompt: Place a small amount of food extract containing alum in a test tube, add dilute hydrochloric acid, and then slowly add barium chloride solution while gently shaking.

Evaluation guide:
(i) Target concept: Visual confirmation of sulfate via barium sulfate precipitation in acidified food extract.
Minimum mechanism: Acidification prevents interference from carbonate/phosphate; barium ions must contact sulfate ions in solution to form crystalline BaSO₄ nuclei that grow into visible white colloidal suspension.
(ii)Storyline: [Frame 0–2] Static shot: test tube holds food extract (opaque or lightly colored liquid). [Frame 3–4] Dropper enters frame, dispenses clear liquid (HCl) into tube; liquid level rises, no immediate change. [Frame 5–6] Second dropper enters, dispenses clear liquid (BaCl₂) into same tube; at point of contact, localized whitening begins. [Frame 7–9] Hand grasps tube, initiates gentle horizontal oscillation; white particles remain suspended, evenly distributed, non-settling. Perspective: fixed frontal close-up; full visibility of tube interior and reagent delivery points; no occlusion of reaction zone during shaking.

Manual:
Experimental Procedure
1. Place food extract containing alum in a test tube.
2. Add dilute hydrochloric acid to the test tube.
3. Slowly add barium chloride solution while gently shaking the test tube.
Observation of Experimental Phenomena
A white precipitate forms immediately after barium chloride addition and remains suspended during shaking.
Summary of Experimental Principles
Aluminum sulfate reacts with barium chloride in acidic medium to form insoluble barium sulfate (white precipitate), confirming sulfate presence.

Prompt Grounding rubric:
level_1: None of the three required objects appear: no test tube, no food extract inside it, and no barium chloride solution shown being added; or the scene is unrelated to this setup entirely.
level_2: Only one of the three objects is shown (e.g., an empty test tube alone), and none of the required actions occur: no acid added, no barium chloride added, no shaking; or two objects appear but the reagents are added in the wrong order (barium chloride before the acid).
level_3: The test tube with food extract, the dilute hydrochloric acid, and the barium chloride solution are all present; the acid is added to the tube, the barium chloride solution is added to the same tube afterward, and gentle shaking follows, but at least one addition is shown going into the wrong container (e.g., acid added to an empty tube, barium chloride added to a separate beaker instead of the test tube) or the reagent source is never visually connected to the test tube.
level_4: The food extract sits in the test tube, the dilute hydrochloric acid is visibly added to that same tube, the barium chloride solution is then visibly added to that same tube, and gentle shaking is applied to that tube right after (all in one continuous shot with a fixed viewpoint and no jump between different tubes), but either the food extract shows no visible turbidity change during or after shaking, the shaking motion is jerky or stops partway through, or one reagent's dropper carries an unlabeled but plausible clear liquid.
level_5: Every object is clearly identifiable by its form: the test tube holding the food extract, a dropper delivering the dilute hydrochloric acid into that tube, a separate dropper delivering the barium chloride solution into the same tube, followed by continuous gentle shaking of that one test tube, all within a single fixed-viewpoint shot; no extra objects enter the frame, there is no cut between the reagent source and the tube, and the acid is never shown appearing after the barium chloride.

Scientific and Causal Correctness rubric:
level_1: No precipitate ever forms; the liquid stays clear and colorless through every addition and through shaking; there is no visible link between adding the barium chloride and any change in the tube.
level_2: A precipitate appears, but with the wrong timing or color: it forms before the barium chloride is added, or right when the acid alone is added, or it is colored (blue, green, yellow) instead of white, or it dissolves away completely during shaking.
level_3: A white precipitate appears only after the barium chloride is added and stays visible during gentle shaking; however, either it also appears before the acid is added, the acid step is skipped, or the precipitate forms in a container other than the test tube holding the food extract and acid.
level_4: A white precipitate appears only after the barium chloride contacts the food extract that already contains the acid, and it persists through shaking without dissolving or changing color, but it is faint and hard to distinguish from the tube's reflections, it appears as one solid clump rather than fine suspended particles, or there is a delay of more than a second before it becomes visible.
level_5: A finely dispersed white precipitate appears promptly once the barium chloride solution reaches the acidified food extract, stays evenly suspended through the gentle shaking with no settling, color shift, or dissolving, and is clearly visible against the tube and liquid, with the timing unmistakably tied to the barium chloride's arrival rather than to the acid alone.

Spatiotemporal Consistency rubric:
level_1: The test tube or a reagent container jumps to a different position between shots with no motion connecting them; the liquid level in the tube changes suddenly with no pour shown; the shaking motion starts or stops with no buildup or slowdown at all; or the lighting flips between very different brightness levels with no cause.
level_2: One clear break in continuity occurs: the test tube rotates by a large angle with no visible turning motion; a droplet of barium chloride appears already in mid-air with no trajectory leading to it; the shaking reverses direction instantly with no slowing first; or the camera cuts to a noticeably different angle with no visual bridge between the two views.
level_3: The test tube, reagent droppers, and liquid keep a consistent position, size, and orientation in frame; no object teleports or reshapes; the shaking shows a continuous back-and-forth motion; but one small flaw is visible, such as the framing wobbling briefly, a short pause partway through one reagent's delivery before it continues, or the tube drifting sideways by more than a quarter of its width with no clear hand motion causing it.
level_4: No object jumps position or changes shape unexpectedly, and there is no sudden lighting flash or shadow jump; the shaking motion is smooth and continuous throughout; each reagent travels in one visible, unbroken path from dropper to tube; scale and perspective stay consistent for every object; the only flaw is something small and non-core, like a brief instant of motion blur that looks a bit stronger than the actual speed would suggest, or the background shifting very slightly as if the camera were handheld.
level_5: The test tube stays fixed in position and orientation throughout; every motion (the dropper's approach, the droplet's fall, and the shaking) looks physically natural and smoothly connected; there is no stutter, no warped edges, and the dropper never appears to pass through the tube's glass wall; lighting and reflections on the tube and liquid stay physically consistent and steady across the whole video.