Domain: Natural Science — Chemistry
Target concept: Ligand Substitution-Induced Solubility Changes: Precipitation and Redissolution

Video generation prompt: On the laboratory bench, two transparent glass beakers contain turbid white silver chloride; ammonia solution is slowly added to the left beaker while stirring, followed by the addition of dilute nitric acid.

Evaluation guide:
(i) Target concept: Ligand substitution-induced solubility change in AgCl via reversible complexation with NH₃, disrupted by acidification.
Minimum mechanism: AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq); Ag⁺ + 2NH₃ ⇌ [Ag(NH₃)₂]⁺ (soluble); H⁺ + NH₃ → NH₄⁺, shifting equilibrium left → AgCl(s) re-precipitates.
(ii)Storyline: Frame 0–2s: Static wide shot of two beakers, both turbid white, side-by-side, fixed viewpoint, no motion. Frame 2–5s: Close-up on left beaker: ammonia dropper enters frame top-right, steady stream contacts surface; simultaneous clockwise stirring begins; turbidity visibly diminishes to full clarity by end of addition. Frame 5–8s: Brief pause (still clear left beaker); nitric acid dropper enters same entry path; stream contacts surface; turbidity fully reappears within 1s of contact. Frame 8–10s: Stable shot confirming left beaker turbid again, right unchanged; no motion except natural particle settling. Visibility constraint: All phenomena must be macroscopically visible, with no reliance on zoom, labels, or annotations; contrast must be sufficient for human observer to distinguish turbid/clear/turbid states unambiguously.

Manual:
Experimental Procedure
1. Place two identical transparent glass beakers side-by-side on bench.
2. Fill both with equal volumes of turbid white silver chloride suspension.
3. Using a dropper, slowly add ammonia solution to the left beaker while stirring continuously.
4. Observe clearing of turbidity.
5. Then add dilute nitric acid to the same left beaker.
6. Observe reappearance of turbidity.
Observation of Experimental Phenomena
- Initial state: both beakers contain uniformly turbid white suspension.
- After ammonia addition + stirring: left beaker becomes fully clear/transparent; right beaker unchanged.
- After nitric acid addition: left beaker returns to turbid white; right beaker remains unchanged.
Summary of Experimental Principles
AgCl precipitate dissolves in ammonia due to [Ag(NH₃)₂]⁺ complex formation, increasing solubility. Subsequent addition of HNO₃ protonates NH₃, destroying the complex and re-precipitating AgCl.

Prompt Grounding rubric:
level_1: No two glass beakers holding turbid white AgCl suspension are shown side by side; no ammonia dropper or nitric acid dropper appears; no stirring action or liquid addition is visible; left and right beakers are not distinguishable from each other at all.
level_2: Two beakers are present side by side, but at least one lacks the turbid white suspension; or ammonia is shown but never directed into the left beaker; or nitric acid appears but is never added after ammonia; or no stirring accompanies the ammonia addition; or it is unclear which beaker is being treated.
level_3: Both beakers start out turbid white and sit side by side; ammonia solution is visibly added into the left beaker while a stirring rod stirs it; dilute nitric acid is subsequently added into that same left beaker; the beakers, droppers, and stirring rod all read as the correct type of lab glassware and are plausibly scaled to bench equipment.
level_4: Everything in level 3 holds, and additionally the left beaker stays clearly identifiable throughout (consistently the one on-screen left), the ammonia dispenser looks visually distinct from the nitric acid dispenser (different bottle shape, cap color, or label), and the stirring motion is confined to the left beaker only during the ammonia step.
level_5: Everything in level 4 holds, and additionally no stray clutter or unrelated objects appear near the setup, both beakers keep one fixed bench position with no repositioning or camera cut, the action strictly follows left-beaker ammonia addition then stirring then nitric acid addition with no simultaneous or reversed steps, and the right beaker is never touched by either reagent.

Scientific and Causal Correctness rubric:
level_1: Turbidity in both beakers stays unchanged no matter what is added; or the left beaker clears without any ammonia reaching it; or it turns turbid again without any nitric acid reaching it; or a color unrelated to AgCl chemistry appears (e.g., yellow or brown tint).
level_2: Turbid white shows up in only one beaker to begin with; or the left beaker clears while the right beaker is treated instead; or clearing happens before the ammonia stream actually contacts the liquid; or the re-turbidity appears before the nitric acid stream contacts the liquid; or the re-formed solid is a different color or texture (gray, blue, or non-particulate haze) than the original AgCl.
level_3: Both beakers begin turbid white; the left beaker becomes clear and transparent during or right after the ammonia addition, consistent with the soluble [Ag(NH3)2]+ complex forming; the same beaker turns turbid white again during or right after the nitric acid addition, consistent with the complex breaking down and AgCl re-forming; the right beaker shows no change at any point.
level_4: Everything in level 3 holds, and additionally the clearing is complete (no leftover haze remains in the left beaker before the nitric acid is added), the re-formed turbidity looks as dense and opaque as the original suspension, and both transitions occur promptly alongside their respective reagent's contact rather than lingering in a partial, in-between state.
level_5: Everything in level 4 holds, and additionally the re-precipitated solid matches the original suspension's fine, uniformly dispersed particulate look (not a surface film, streaky swirl, or bubbles that would suggest a different mechanism), and each transition is triggered strictly and only by its own reagent's contact, with no overlapping or spontaneous changes in either beaker.

Spatiotemporal Consistency rubric:
level_1: Either beaker is missing from a frame and then suddenly present again moments later with no visible transition between; a beaker's size or shape distorts abruptly; the overall brightness snaps between bright and dark with no transition; the stirring rod drops out of the shot mid-stir and reappears; the contents of a beaker flicker or blank out intermittently; a hard camera cut interrupts the shot.
level_2: The stirring rod's position jumps without passing through any intermediate position; the added liquid's stream vanishes mid-air before it reaches the surface; a beaker's rim bends or warps in a way glass wouldn't; the shadows cast by the beakers swing to a different, inconsistent direction between adjacent frames; the suspended AgCl particles become invisible through the beaker wall at moments when they should still be visible.
level_3: Neither beaker vanishes, warps, or reflects an inconsistent light direction; the stirring rod traces a continuous circular path inside the left beaker; the added reagent forms an unbroken stream or falling drop rather than jumping into place; both beakers keep a consistent wall thickness, curvature, and refraction look from frame to frame.
level_4: Everything in level 3 holds, and additionally any camera drift moves near and far objects together in proportion; the liquid surface dips or ripples plausibly right where a drop lands; there is no strobing, ghosting, or tearing between frames; the stirring rod keeps the same position relative to the beaker it stirs; drops fall and stirring proceeds at a steady, uniform pace with no visible speed change or skip.
level_5: Everything in level 4 holds, and additionally the curved glass and liquid consistently bend the view of whatever sits behind them (for example, the far beaker's rim or the bench edge visibly distorts through the near beaker's curved wall) the same way in every frame; the suspended AgCl particles neither streak downward nor pile up unnaturally at the bottom during the still phases; no frame is a frozen repeat or loop; the edges of both beakers, the dropper, and the stirring rod stay crisply defined while moving; the stirring rod is never rendered behind a beaker wall when it should visibly pass in front of it.