Domain: Natural Science — Chemistry
Target concept: Dialysis tubing membrane, carbon dioxide diffuses into bromothymol blue solution

Video generation prompt: A transparent beaker containing a blue bromothymol blue solution, in which a sealed dialysis tube is immersed. The dialysis tube is filled with exhaled air and the dialysis membrane is in contact with the surrounding liquid.

Evaluation guide:
(i) Target concept: Diffusion-driven acidification of pH indicator via semi-permeable membrane.
Minimum mechanism: Dialysis membrane must be permeable to CO₂ but impermeable to liquid and large molecules; bromothymol blue must be in aqueous solution at initial pH >7.6 (blue); exhaled air must contain sufficient CO₂ (~4–5%) to induce detectable pH shift; membrane–solution contact must be direct and sustained for diffusion to occur.
(ii)Storyline: Frame 0–2s: Static shot of transparent beaker filled with uniform blue solution. Frame 2–4s: Dialysis tube (sealed, gas-filled, visibly empty interior) enters frame and descends continuously into solution. Frame 4–5s: Tube achieves full submersion and stable vertical position; membrane makes uninterrupted contact with surrounding liquid. Frame 5–10s: Green color appears first as a thin band precisely at the tube–liquid interface, then expands radially while maintaining sharp blue–green boundary; no green appears outside contact zone or before full immersion; tube remains motionless and intact; lighting and perspective remain fixed.

Manual:
Experimental Procedure
1. Fill a transparent beaker with bromothymol blue solution until it appears uniformly blue.
2. Seal both ends of a dialysis tube and fill it with exhaled air.
3. Gently immerse the sealed dialysis tube vertically into the beaker so the entire tube is submerged and the membrane contacts the solution.
Observation of Experimental Phenomena
The blue solution adjacent to the dialysis tube gradually turns green, beginning at the membrane–liquid interface and spreading outward over time.
Summary of Experimental Principles
CO₂ from exhaled air diffuses through the semi-permeable dialysis membrane into the bromothymol blue solution, lowering pH and causing the indicator to change from blue (basic) to green (neutral).

Prompt Grounding rubric:
level_1: The transparent beaker, blue bromothymol blue solution, sealed dialysis tube, and gas-filled interior described in the prompt are not shown together: e.g., no beaker appears, the liquid is not blue, no dialysis tube is present, or the tube is never placed into the liquid.
level_2: A beaker and a tube-like object appear, but at least one core element is wrong or missing: the beaker is opaque or its liquid is not blue, the tube is a rigid rod or pipette rather than a flexible sealed dialysis tube, or the tube is shown resting outside the liquid rather than immersed in it.
level_3: A transparent beaker holding visibly blue liquid contains a sealed, cylindrical dialysis tube that is fully immersed; the tube's interior looks empty and gas-filled rather than liquid-filled, matching the prompt's basic object list and arrangement.
level_4: All of score 3 holds, and the dialysis membrane is shown pressed directly against the surrounding blue liquid with no visible gap or air pocket; the tube stays upright and centered in the beaker, and no hand, label, or other prop covers the tube-liquid contact area.
level_5: All of score 4 holds, and the tube remains centered in view with its membrane evenly wetted along its whole submerged length (no dry patch or visible meniscus gap); the beaker glass shows no warping that hides the tube-liquid boundary, and the tube and beaker stay unobstructed and unblurred for the entire 10-second clip.

Scientific and Causal Correctness rubric:
level_1: The solution never turns green anywhere in the beaker and stays blue the whole clip; or green/yellow coloring appears with no tube present, before the tube touches the liquid, or in a different container than the one holding the tube.
level_2: The liquid changes from blue toward green or yellow either before the tube is fully immersed or after the tube has already been lifted back out; or only an isolated patch of solution far from the tube changes color while the region touching the membrane does not; or the tube itself is shown holding liquid rather than trapped air.
level_3: After the sealed, air-filled dialysis tube is fully immersed and its membrane is touching the solution, the blue liquid nearest the membrane visibly turns green, with the color change starting at the tube's surface and spreading outward into the beaker; the change happens only once immersion and contact are established, not earlier or later.
level_4: All of score 3 holds, and the greening stays confined close to the tube (roughly within one tube-width of its surface) and advances steadily outward without jumping or skipping; once liquid near the tube has turned green it does not revert to blue, and the tube itself stays sealed and undamaged.
level_5: All of score 4 holds, and the green region hugs only the membrane's wetted surface — no green appears above the liquid line or beneath the tube's lower end; the blue-to-green boundary stays a clean, steady line rather than flickering or blending unevenly; no unrelated color such as purple or brown appears, and the green shade matches the expected bromothymol-blue color for a CO2-driven pH drop rather than looking too dull or too saturated.

Spatiotemporal Consistency rubric:
level_1: The dialysis tube appears inside the beaker with no visible entry motion, as if placed there instantly between frames; the tube suddenly rotates more than 90 degrees between one frame and the next with no visible motion connecting the two orientations; the liquid level jumps up or down with no pouring or immersion cause; the beaker cracks, melts, or changes shape partway through; or the whole scene's brightness swings sharply from one frame to the next with no clear light-source change.
level_2: The tube's descent into the liquid is visibly cut or skipped partway through; the liquid surface changes height for no visible reason once the tube is already inside; the tube separates from the liquid and reattaches without a continuous path; or the shadow cast by the beaker or tube swaps to the opposite side abruptly with no matching change in the light source.
level_3: The tube moves into the beaker along one continuous path with no cuts or skips; once submerged, the liquid surface settles smoothly rather than sloshing indefinitely; the tube keeps the same tilt relative to the beaker throughout; the beaker and tube keep their shape with no cracking, warping, or loss of transparency.
level_4: All of score 3 holds, and the tube comes to a complete stop once fully submerged and stays still for at least 3 seconds; ripples on the liquid surface die down naturally rather than continuing indefinitely; the tube's position relative to the beaker wall does not drift, and no duplicate or ghost outline of the tube appears.
level_5: All of score 4 holds, and the tube reaches full contact with the liquid in one smooth motion without pausing partway and resuming; the liquid surface wraps evenly around the tube on all sides with no lopsided bulge; the tube and liquid show no visible shaking, flicker, or strobing, and the beaker rim, tube ends, and liquid surface all stay sharp and steady rather than blurring or warping across frames.