Domain: Natural Science — Chemistry
Target concept: Brown colloidal to brown precipitate, then to yellow solution

Video generation prompt: A test tube containing an appropriate amount of ferric hydroxide colloidal solution had dilute sulfuric acid added to it gradually, drop by drop. The test tube was observed throughout the addition.

Evaluation guide:
(i) Target concept: Acid-induced coagulation and subsequent dissolution of ferric hydroxide colloid.
Minimum mechanism: Colloidal stability must be disrupted by electrolyte (H⁺/SO₄²⁻) to form visible precipitate; excess strong acid must protonate hydroxide ligands to yield soluble hexaaquairon(III) complex with characteristic yellow color; no redox or decomposition occurs.
(ii)Storyline: Frame 0–2s: Static shot of upright test tube with brown cloudy liquid (colloid). Frame 2–4s: Dropper enters frame, approaches tube mouth, begins first drop addition → immediate localized turbidity increase and brown particle nucleation at liquid surface. Frame 4–6s: Particles aggregate and settle as distinct brown sediment layer. Frame 6–8s: Further drops cause gradual shrinking of sediment layer with visible upward diffusion of yellow hue. Frame 8–10s: Sediment fully vanishes; entire solution is uniformly yellow and transparent; dropper remains visible at mouth, no residual particles or cloudiness.

Manual:
Experimental Procedure
1. Place a test tube containing ferric hydroxide colloidal solution (brown, cloudy liquid) upright on stand.
2. Using a dropper, gradually add dilute sulfuric acid dropwise into the test tube.
3. Observe continuously until precipitate forms, then dissolves.
Observation of Experimental Phenomena
- Initial: Brown, cloudy colloidal solution.
- During titration: Brown precipitate forms and settles.
- Final: Precipitate dissolves completely, yielding a clear yellow solution.
Summary of Experimental Principles
Ferric hydroxide colloid coagulates to brown Fe(OH)₃ precipitate upon electrolyte addition; excess H₂SO₄ dissolves it via acid–base reaction forming soluble yellow [Fe(H₂O)₆]³⁺ complex.

Prompt Grounding rubric:
level_1: No test tube appears; or no liquid is visible inside it; or nothing resembling a titration (no dropper, no liquid being added) ever happens in the clip — the scene has no lab setting connecting a container, a liquid, and an add-drops action.
level_2: A test tube holding some liquid is shown, but no dropper, pipette, or other delivery tool is ever visible; or a tool is shown but never actually adds liquid into the tube (no drop leaves the tool and enters the tube); the described drop-wise addition never actually takes place.
level_3: A test tube holding a liquid is shown, and a dropper or pipette approaches and touches (or nearly touches) the tube's mouth; at least one distinct addition of liquid into the tube is visible; the tools used are recognizably a test tube and a dropper/pipette (not, e.g., a beaker standing in for the tube or a syringe standing in for the dropper).
level_4: The test tube is upright with its mouth clearly the entry point for the dropper; the dropper visibly delivers liquid in at least two separate, countable additions rather than one continuous pour; no equipment is substituted for something else, and the dropper is never shown already inside the tube without first approaching from outside.
level_5: The test tube stays upright and centered in frame for the whole clip; the dropper approaches vertically from above, makes contact at the tube's mouth, and delivers at least three separate, clearly countable additions along a consistent path; the test tube and dropper are never blocked from view by any other object; no unrelated tools enter the shot; the tube itself never shifts position or tips over during the sequence.

Scientific and Causal Correctness rubric:
level_1: Across the whole clip the liquid keeps one unchanging color from start to finish; no precipitate ever forms, and the yellow endpoint described in the process is never reached.
level_2: The starting liquid is not the expected brown colloidal appearance (e.g., it looks clear, blue, or white); or a precipitate forms but in the wrong color (black, gray, or green rather than brown); or the liquid never becomes yellow by the end (e.g., it stays brown, turns orange, or goes clear/colorless); the acid addition doesn't appear to be what's driving any color change shown.
level_3: The liquid starts brown and cloudy/turbid, consistent with a colloid; after some acid has been added, a brown particulate mass forms and settles toward the bottom; with continued addition, that brown solid shrinks away and the liquid becomes clear yellow; all three stages (cloudy brown, brown sediment, clear yellow) are present, though the transitions between them may be abrupt or the sediment stage brief.
level_4: The brown, hazy colloidal starting liquid gives way to a visibly distinct settled brown solid as acid is added; continued addition then causes that brown solid to shrink and disappear, leaving a uniformly yellow, clear liquid with no remaining haze or particles; the three stages occur strictly in order (colloid -> precipitate -> yellow solution) without skipping the precipitate stage or reversing direction.
level_5: The starting colloid is unmistakably brown and turbid; the brown precipitate that forms has a clear, sharp-edged boundary against the surrounding liquid rather than a fuzzy blend; the precipitate shrinks and fully disappears with continued acid addition, never partially regrowing; the end liquid is evenly yellow and fully clear with no specks or cloudy patches left anywhere in the tube; each stage transition is visibly tied to an acid addition rather than happening on its own between additions.

Spatiotemporal Consistency rubric:
level_1: The test tube suddenly appears in a different position, size, or orientation between frames with no motion shown in between; the dropper or the liquid inside the tube is suddenly missing from one frame and back the next, with nothing shown causing it to leave or return; the overall brightness of the shot swings sharply from one frame to the next as if from a different take; the tube's shape visibly bends, bulges, or breaks on its own; the camera jumps between clearly different viewpoints (e.g., side view to top-down) with no transition.
level_2: The test tube tilts or spins by more than roughly 15 degrees with nothing touching it; the dropper's path is jerky or zig-zags instead of moving smoothly toward the tube; the liquid surface goes from calm to violently splashing and back to calm with no addition event to explain it; the tube's shadow swings to a clearly different angle even though the light source and the tube haven't moved; background objects in the shot blink or shift position abruptly.
level_3: The test tube stays upright and in the same spot in the frame; the dropper moves at a believable, smooth pace as it approaches and touches the tube's mouth; the liquid's surface reacts in a way that plausibly matches each addition (a small ripple or swirl, not a violent splash or a frozen surface); the shadow the tube casts stays believably matched to a single unmoving light source rather than swinging around on its own; the tube's shape and walls stay intact with no visible clipping or bending.
level_4: The test tube shows no unexplained sliding or tilting across the entire clip; the dropper keeps a steady, near-vertical path and roughly constant distance from the tube's mouth as it delivers each addition; each addition causes a small, localized disturbance in the liquid (a brief ripple or swirl near the surface) that settles back down before the next addition; the background stays static and evenly lit throughout; the tube and dropper never appear to overlap or pass through one another in a way that breaks their solid shapes.
level_5: All 4-point conditions hold, and additionally: the test tube's position in frame does not drift at all from the first addition to the last; the dropper's path stays a clean, near-straight line from its entry into frame to contact with the tube; each addition produces a similar small ripple that fully settles before the next drop lands; the liquid level rises gradually and smoothly rather than jumping between frames; the camera viewpoint and focus stay fixed for the whole clip with no sudden refocusing or angle change.