Domain: Engineering — Civil & Environmental Engineering
Target concept: Copper Ion Wastewater Treatment

Video generation prompt: Two beakers containing 100 mL of 0.1 mol/L copper ion solution were placed side by side. Sodium sulfide solution of 0.2 mol/L was added to the left beaker, while no addition was made to the right one. After stirring, the solutions were allowed to settle, and continuous images were captured for several seconds.

Evaluation guide:
(i) Target concept: Selective precipitation of Cu²⁺ via sulfide addition as a wastewater treatment mechanism.
Minimum mechanism: Presence of aqueous Cu²⁺ (blue/green color), addition of S²⁻ source, formation of insoluble CuS (black/brown solid), gravitational settling of dense precipitate, and persistence of untreated control showing no reaction.
(ii)Storyline: Frame opens with two identically filled beakers side-by-side → sodium sulfide addition occurs exclusively to left beaker (visible tool contact) → gentle stirring applied only to left beaker → stirring ceases → both beakers held static in fixed viewpoint → dark particulate matter appears and descends vertically in left beaker while remaining absent in right → final state shows sediment layer at bottom of left beaker and homogeneous liquid in right beaker; entire sequence must be captured from a stable frontal or slightly angled overhead perspective ensuring full visibility of both beaker interiors and sediment formation without occlusion.

Manual:
Experimental Procedure
1. Place two identical transparent glass beakers side-by-side, each filled with 100 mL of aqueous copper ion solution (visually blue or greenish-blue).
2. Add sodium sulfide solution to the left beaker only; stir gently.
3. Cease stirring and observe both beakers as they settle for several seconds.
Observation of Experimental Phenomena
- Left beaker: rapid formation of dark-colored (black/brown) particulate precipitate that settles to the bottom; supernatant becomes progressively clearer.
- Right beaker: no precipitate forms; solution remains uniformly colored and transparent.
Summary of Experimental Principles
Copper ions (Cu²⁺) react with sulfide ions (S²⁻) to form insoluble copper sulfide (CuS), a black precipitate — a key method for removing heavy metals from wastewater.

Prompt Grounding rubric:
level_1: Only one beaker is shown, or the two beakers are not placed next to each other, or neither beaker shows sodium sulfide solution being added, or the untreated (right) beaker is missing entirely.
level_2: Two beakers appear but are positioned apart rather than side by side, or it's unclear which beaker (if either) receives the sodium sulfide addition, or there's no distinguishable pause where the liquids are left undisturbed to settle.
level_3: Two beakers filled with blue or blue-green liquid sit side by side; a dropper, pipette, or stream visibly adds liquid into the left beaker only, with the right beaker receiving no addition; stirring is shown at least in the left beaker; afterward both beakers appear to sit undisturbed while the liquids settle.
level_4: The added sodium sulfide never touches or splashes into the right beaker; stirring is confined to, or clearly more vigorous in, the left beaker only; once stirring ends, no hands, tools, or other objects re-enter the frame near either beaker during the settling period.
level_5: The pipette or stream makes contact only with the left beaker's liquid, with no drips or splashes reaching the right beaker; stirring stops cleanly before the settling period begins; throughout the settling period, both beakers stay fully visible with nothing entering the frame to block or disturb either one.

Scientific and Causal Correctness rubric:
level_1: Neither beaker's liquid changes appearance after the addition step: no darkening, no cloudiness, and no settling solid forms in either beaker.
level_2: A change happens in one beaker but is the wrong kind for this reaction: for example the liquid turns yellow or clear, or a floating white haze appears, rather than a dark solid that sinks; or the two beakers end up looking identical by the end.
level_3: The left beaker develops dark (black or dark brown) solid particles that sink and collect at the bottom over time, while the right beaker's blue or blue-green liquid stays clear and unchanged with no particles at all; by the end, only the left beaker has a visible layer of dark sediment at the bottom.
level_4: The dark sediment forms only in the left beaker and nowhere in the right beaker at any point in the sequence; once settled, the sediment in the left beaker stays put at the bottom rather than re-mixing or dissolving back into the liquid above it.
level_5: The dark sediment begins appearing soon after the sodium sulfide is stirred in, without an unexplained delay, and as it accumulates at the bottom of the left beaker, the liquid layer above it visibly becomes less blue and more colorless (consistent with copper ions being removed from solution), while the right beaker's color and clarity stay exactly as they started.

Spatiotemporal Consistency rubric:
level_1: A beaker's position or size changes abruptly between frames, the stirring rod or motion jumps to a different angle without a smooth transition, the light on the scene changes abruptly for no visible reason, or a liquid's surface level jumps instead of moving smoothly.
level_2: The dark particles in the left beaker appear suddenly at full size instead of gradually forming and growing; the stirring motion is jerky or skips between disconnected positions; a beaker's reflection or shadow moves independently of the beaker itself.
level_3: Both beakers stay in the same position and orientation throughout; the stirred liquid's surface moves in a physically believable way (small ripples, a swirl that gradually calms) rather than jumping; the dark particles that form in the left beaker sink gradually rather than appearing instantly at the bottom; the light's direction and brightness look the same at the end of the clip as at the start.
level_4: The beaker walls don't warp or bulge at any point; the dark particles don't flicker in and out between frames; their downward drift doesn't suddenly speed up, stop, and restart; the two beakers keep the same size relationship to each other and to the background throughout.
level_5: The stirring rod follows one smooth, continuous circular path rather than jumping between positions; the particles drift downward along smooth paths rather than zig-zagging or freezing mid-fall; the transition from stirring to settling plays as one continuous shot, with the camera holding a steady, unchanging view of both beakers rather than cutting, zooming, or repositioning at any point.