Domain: Natural Science — Chemistry
Target concept: Sodium carbonate saturated solution precipitates crystals upon contact with carbon dioxide gas.

Video generation prompt: A test tube contains an appropriate amount of saturated sodium carbonate solution. Carbon dioxide gas is continuously introduced into the solution in the test tube until it is in excess, and changes in the solution within the test tube are observed.

Evaluation guide:
(i) Target concept: Precipitation of sodium bicarbonate via CO₂-induced conversion of carbonate to bicarbonate in saturated solution.
Minimum mechanism: CO₂ must dissolve and react to form HCO₃⁻; local supersaturation of NaHCO₃ must exceed solubility limit; nucleation and growth of solid NaHCO₃ crystals must occur visibly in situ.
(ii)Storyline: [Frame 0–2] Static shot: upright test tube with clear liquid, gas inlet positioned above liquid surface. → [Frame 3–4] Inlet tip contacts liquid surface; first bubbles enter. → [Frame 5–7] Bubbles rise steadily; localized turbidity appears near inlet tip. → [Frame 8–9] Distinct white granular crystals become visible, increasing in number and settling downward. → Perspective: Fixed frontal close-up; entire test tube and inlet fully visible; no occlusion; top-down lighting to enhance crystal visibility against transparent liquid background.

Manual:
Experimental Procedure
1. A clean vertical test tube contains a colorless transparent saturated sodium carbonate solution.
2. A narrow gas inlet tube is inserted into the solution, and carbon dioxide gas is introduced continuously.
Observation of Experimental Phenomena
White crystalline precipitate forms and accumulates in the solution during gas introduction.
Summary of Experimental Principles
Sodium carbonate saturated solution reacts with CO₂ to form less-soluble sodium bicarbonate, whose solubility limit is exceeded in the saturated, common-ion-rich solution, causing it to precipitate as white crystals.

Prompt Grounding rubric:
level_1: Scene lacks a test tube, or shows no colorless liquid inside one, or omits any gas-delivery tubing, or never shows gas being introduced into the liquid.
level_2: A test tube with liquid is shown, but the liquid is not presented as the saturated sodium carbonate solution described (e.g., it is colored, cloudy, or clearly absent from the setup), and/or no gas inlet tube is visible entering the tube, and/or no bubbling or gas stream is shown entering the liquid.
level_3: An upright test tube holds a colorless transparent liquid consistent with the described saturated sodium carbonate solution; a narrow gas inlet tube is inserted into the liquid; a continuous stream of bubbles enters the liquid from the inlet tip, indicating CO2 is being introduced as described.
level_4: Everything in score 3 holds, and additionally the test tube stays upright and does not tip or move during the clip; the inlet enters from above the liquid and its tip stays submerged; the bubble stream is continuous rather than sporadic; no other reagents, tools, or liquids are added to the tube.
level_5: Everything in score 4 holds, and additionally the test tube and inlet remain centered in a steady, unchanging camera framing; the liquid starts free of any visible particles before gas contacts it; the inlet is a thin rigid tube whose outline stays clearly distinguishable from the liquid at all times.

Scientific and Causal Correctness rubric:
level_1: No precipitate ever forms in the liquid, or the liquid changes color or turns uniformly cloudy in a way inconsistent with discrete white crystal formation, or a precipitate is shown appearing outside the test tube, or the bubbling causes no visible change to the liquid at all.
level_2: A precipitate appears but is the wrong color (e.g., yellow or blue) or texture (e.g., an oily film or gel rather than granular crystals), or precipitate is already present in the liquid before any bubbles arrive, or the precipitate dissolves back into a clear liquid once formed.
level_3: After bubbles begin entering the liquid, a white, granular, crystalline precipitate becomes visible within it; the precipitate is distinguishable from the surrounding solution as an undissolved solid, and the liquid itself does not turn cloudy or colored on its own.
level_4: Everything in score 3 holds, and additionally the precipitate appears only after gas has entered the liquid, never beforehand; once formed, it does not redissolve while gas continues to bubble through; the surrounding liquid stays colorless throughout.
level_5: Everything in score 4 holds, and additionally the precipitate keeps a granular, crystalline look rather than turning into sludge or a surface film; the amount of precipitate increases gradually as gas keeps bubbling in rather than appearing all at once; the liquid above the settling crystals stays visibly clear.

Spatiotemporal Consistency rubric:
level_1: The test tube, gas inlet, or precipitate appears to vanish and instantly reappear at a different position or size between adjacent frames; the liquid height changes with no continuous transition; the scene's lighting flips brightness or direction abruptly from one frame to the next.
level_2: The test tube visibly wobbles or rotates by more than roughly 30° between frames with no driving cause, or the liquid surface tilts by more than roughly 20° and stays tilted; a patch of precipitate appears at full density in one frame with nothing visible in the previous frame; rising bubbles change size or direction inconsistently in a way that looks physically implausible.
level_3: The test tube stays fixed in position and orientation across the clip; the liquid surface stays level aside from small ripples from bubbling; precipitate that appears builds up gradually over several consecutive frames rather than flickering in and out; bubbles rise at a steady rate.
level_4: Everything in score 3 holds, and additionally bubbles ascend smoothly without freezing or stuttering; the visible amount of precipitate increases incrementally frame to frame rather than jumping; shadows and highlights on the tube's glass surface do not jump or flicker.
level_5: Everything in score 4 holds, and additionally the distance between the inlet tip and the liquid surface stays constant throughout; settling precipitate moves downward without sudden sideways jumps; the inlet and precipitate never occlude each other in a way that contradicts their established depth order from one frame to the next.