Domain: Natural Science — Chemistry
Target concept: Reaction between Sodium Sulfate and Barium Hydroxide

Video generation prompt: A test tube contains a colorless sodium sulfate solution, and barium hydroxide solution is added using a pipette.

Evaluation guide:
(i) Target concept: Double displacement reaction producing an insoluble ionic compound (BaSO₄) as visual evidence of chemical change.
Minimum mechanism: Two aqueous electrolyte solutions must mix; ions must dissociate freely; Ba²⁺ and SO₄²⁻ must encounter each other to nucleate solid-phase BaSO₄ crystals; crystal formation must scatter visible light sufficiently to produce macroscopic white turbidity.
(ii)Storyline: Frame 0–2: Static shot of upright test tube containing homogeneous, colorless, transparent liquid (Na₂SO₄). Frame 3–4: Pipette enters top of frame, aligned vertically over tube mouth; no liquid yet visible in tip. Frame 5: First droplet of clear liquid (Ba(OH)₂) makes contact with surface of colorless solution. Frame 6: White turbidity appears *at point of contact* and expands radially downward. Frame 7–9: Entire liquid column becomes uniformly cloudy and opaque white; no settling observed within 10s. Perspective: Fixed frontal view, eye-level, centered on test tube; tube occupies ~40% of frame height; pipette tip always visible above tube mouth; no occlusion of liquid interior.

Manual:
Experimental Procedure
1. Place a clean test tube upright on bench.
2. Fill test tube halfway with colorless sodium sulfate solution.
3. Using a clean pipette, draw barium hydroxide solution from its container.
4. Position pipette tip directly above test tube mouth.
5. Gently dispense barium hydroxide solution into the test tube.
Observation of Experimental Phenomena
A dense, white precipitate forms immediately upon mixing; the solution becomes uniformly cloudy and opaque white; no color change occurs; precipitate remains suspended before settling.
Summary of Experimental Principles
Sodium sulfate (Na₂SO₄) reacts with barium hydroxide (Ba(OH)₂) to form insoluble barium sulfate (BaSO₄, white precipitate) and sodium hydroxide (NaOH, soluble): Na₂SO₄ + Ba(OH)₂ → BaSO₄↓ + 2NaOH.

Prompt Grounding rubric:
level_1: No test tube is shown; no colorless liquid appears in any container; no pipette is present; no second liquid is being added; none of the setup elements from the prompt appear at all.
level_2: A test tube with liquid is shown but the liquid is not colorless (tinted or cloudy from the start), or a pipette appears but never delivers liquid into the tube, or the second solution is shown in a separate container but never brought into contact with the tube's liquid.
level_3: A test tube holding a colorless liquid is shown, and a pipette delivers liquid into it from above; both the tube's liquid and the pipette's liquid read as distinct, identifiable solutions (sodium sulfate and barium hydroxide), but there's no clear moment of entry, e.g. the pipette tip stays outside the tube, or the drop appears to hang in mid-air without visibly reaching the liquid.
level_4: Everything in level 3 holds, plus the delivered liquid is clearly shown entering the tube (a visible stream or falling drop reaching the liquid surface) with no duplicated or misplaced objects and no break in the setup sequence, but one small flaw remains, such as the pipette held at an odd angle, a brief jitter during delivery, or the tube mouth partly hidden from view for a moment.
level_5: A single test tube of clearly colorless liquid sits still in frame; the pipette enters from above, lines up over the tube mouth, and delivers its liquid continuously and visibly into the tube with no gap, hover, or bounce; both solutions read as distinct from start to finish; every object keeps consistent size, position, and orientation; the setup and delivery sequence shows no spatial or ordering anomaly.

Scientific and Causal Correctness rubric:
level_1: No precipitate ever forms; the liquid stays fully clear and uniform before, during, and after the addition; there's no visible link between adding the second liquid and any change inside the tube.
level_2: A precipitate does appear but is the wrong color (yellow or gray rather than white), or it appears before the second liquid is added, or it shows up only inside the pipette tip or outside the tube instead of in the mixed liquid, or the liquid turns into a colored solution instead of forming a white solid.
level_3: A white precipitate forms only after the second liquid contacts the tube's liquid, staying confined inside the tube and clearly distinct from the original clear liquid, but it appears fully formed in a single instant rather than building up, or coexists with patches of unexplained lingering clarity, or clumps only at the bottom with no sign of spreading through the liquid.
level_4: The white precipitate forms only after contact, stays confined to the liquid inside the tube, and visibly thickens or spreads as the two liquids mix, with no color change in the liquid above and no unrelated effects (no bubbling, no separated layers), but one small flaw remains, such as the precipitate looking somewhat translucent rather than a solid opaque white, or staying clumped only where the drop landed instead of spreading through the column.
level_5: As soon as the two liquids touch, a fine white cloudiness spreads through the whole liquid column with no lag, matching the expected look of a barium sulfate precipitate (dense and matte white, not translucent or tinted), while the liquid was unambiguously clear and colorless right up until that contact; the turbidity visibly begins right where the drop meets the surface, with no perceptible delay between contact and the first sign of cloudiness.

Spatiotemporal Consistency rubric:
level_1: The test tube is missing from one frame and inexplicably present again in the next, with no continuous shot bridging the two; the pipette jumps from one part of the frame to another with no path of motion in between; the added liquid shows up at the bottom of the tube with no visible stream connecting it to the pipette tip; the frame's brightness flips suddenly with no transition; the tube appears to rotate or flip with no continuous motion; part of the tube's structure (its base, for instance) drops out of view mid-shot.
level_2: The test tube shifts sideways by more than a third of its width between frames; the pipette's approach is jerky, pausing or reversing direction more than once; the liquid stream blinks on and off more than once during delivery; the tube's cast shadow swings to a different direction abruptly; background elements stretch or resize inconsistently.
level_3: The test tube stays in a fixed position and orientation; the pipette's approach is one continuous motion toward the tube mouth; the added liquid shows an unbroken path from the pipette tip into the tube; the illumination on the tube stays visually steady with no abrupt swing in brightness or shadow direction; nothing in the shot visibly warps, aside from one small flaw, such as the pipette tip briefly grazing the rim without any bounce, or a single blurred frame right as the drop enters.
level_4: The test tube's position stays fixed; the pipette approaches along one smooth, consistent path and slows naturally as it nears the tube; the liquid stream keeps a consistent shape and opacity throughout delivery; lighting, focus, and viewing angle stay steady throughout, aside from one small non-disruptive flaw, such as a slight shift in background blur from depth of field, or a brief soft-focus moment on the tube wall while the rest of the shot stays sharp.
level_5: The test tube stays visibly still and in the same place across the entire clip; the pipette's path toward the tube mouth reads as smooth and direct with no visible jitter; the liquid stream stays continuously visible, uniform in thickness and opacity, with no gaps or sudden warps; lighting, focus, and camera angle all stay effectively constant throughout; there is no visible motion blur, jitter, or depth inconsistency anywhere in the shot.