Domain: Natural Science — Chemistry
Target concept: Reaction between aluminum sulfate and sodium hydroxide solution

Video generation prompt: A test tube contains 5 mL of colorless aluminum sulfate solution. Using a dropper, a small number of drops (about 5 to 10 total, not continued beyond that) of dilute sodium hydroxide solution are added into the tube one drop at a time.

Evaluation guide:
(i) Target concept: Precipitation of aluminum hydroxide when a small, deliberately limited amount of sodium hydroxide is added dropwise to an aluminum sulfate solution.
Minimum mechanism: Al3+ ions are present throughout in the tube; OH- ions are delivered a few drops at a time and only in the small quantity specified by the prompt, never continued into the large excess of NaOH that would be needed to redissolve the hydroxide as [Al(OH)4]-; once enough drops have landed to locally exceed the solubility product, Al(OH)3 nucleates and stays suspended for the remainder of the limited addition shown.
(ii)Storyline: Frame 1-2: Static shot of upright test tube containing colorless solution. Frame 3-4: Dropper enters top of frame, aligned vertically above tube opening. Frame 5-6: First drop detaches and falls; solution unchanged. Frame 7-8: Second/third drop impacts; white precipitate nucleates and becomes visible. Frame 9-10: Precipitate accumulates with each of the small number of additional drops shown; remains uniformly suspended; tube and dropper remain fixed; addition stops after roughly 5-10 drops total, well short of any large excess. Visibility constraint: Entire tube interior (including bottom 1/3) must be unobstructed; dropper tip must remain fully in frame during delivery; no hand or equipment intrusion.

Manual:
Experimental Procedure
1. Place a clean test tube vertically.
2. Add 5 mL of colorless aluminum sulfate solution into the test tube.
3. Using a dropper, add a small, limited number of drops (about 5 to 10 total) of sodium hydroxide solution dropwise into the tube, stopping well before reaching a large excess.
Observation of Experimental Phenomena
A white precipitate forms gradually during the dropwise addition and remains suspended in the solution; because the NaOH added is kept well below the amount needed to redissolve it, no dissolution or color change occurs over the course of this limited addition.
Summary of Experimental Principles
Aluminum sulfate reacts with sodium hydroxide to form insoluble aluminum hydroxide: Al₂(SO₄)₃ + 6NaOH → 2Al(OH)₃↓ + 3Na₂SO₄. The white gelatinous precipitate is Al(OH)₃, which is amphoteric and would redissolve in a large excess of NaOH to form soluble [Al(OH)₄]⁻ (sodium aluminate) — this demo intentionally stops well short of that excess, so only precipitate formation is shown.

Prompt Grounding rubric:
level_1: No test tube is shown, or the tube contains no liquid; the aluminum sulfate solution is missing, is a color other than clear/colorless, or is already cloudy before any sodium hydroxide is added; no dropper or NaOH source appears at any point in the video.
level_2: A test tube with a colorless liquid is visible, but at least one required element is wrong or missing: the liquid is already colored or precipitate-laden in the first frame, the NaOH is poured or splashed in rather than dispensed drop by drop, or the dropper never approaches the tube opening.
level_3: A single upright test tube holds about 5 mL of a clear, colorless liquid; a dropper positioned above the tube opening releases sodium hydroxide solution into it one drop at a time; the tube and dropper are both fully visible for the whole clip, and the dropper only enters the frame after the tube already contains liquid.
level_4: Everything described at the 3-point level is present, and in addition the dropper tip stays centered over the tube opening for the entire sequence, the tube never tips or slides on the table, and no hand, label, or second tube intrudes into the shot.
level_5: Everything described at the 4-point level is present, and in addition each drop of NaOH falls as one separate droplet rather than a continuous stream, with no two drops merging in mid-air; every drop lands on the liquid surface itself rather than striking the tube wall or missing the tube; the camera's framing and distance to the tube stay fixed from the first frame to the last.

Scientific and Causal Correctness rubric:
level_1: No white solid ever forms; the liquid stays perfectly clear through every drop, or any solid that appears is a color other than white (e.g., blue, green), or a precipitate appears with no visible connection to any drop of NaOH landing.
level_2: A white cloudiness appears, but only well after the drops have stopped, or the cloudiness that first appears clears back up before the small, bounded number of drops in this demo (roughly 5-10) has finished; the color that appears is a dingy gray rather than white.
level_3: A white precipitate first becomes visible within the first few drops of NaOH and grows visibly denser as each subsequent drop, within the small bounded total shown, lands; it never clears back to a transparent solution, and it stays suspended through the liquid rather than only clinging to the glass wall.
level_4: Everything at the 3-point level holds, and in addition no single drop causes the precipitate to reverse or thin out (once cloudiness appears after a drop it never regresses on a later drop in this same short sequence), and the very first drop shows no visible change, consistent with the small volume of aluminum sulfate needing at least a couple of drops before local supersaturation is reached.
level_5: Everything at the 4-point level holds, and in addition the precipitate looks white and gelatinous rather than crystalline or grainy, no gas bubbles or fizzing appear at any drop, and the tube's liquid never returns to full transparency after the last of the small number of drops has been added, matching the outcome expected when NaOH is kept well short of the amount that would redissolve the precipitate.

Spatiotemporal Consistency rubric:
level_1: The test tube's position or tilt changes abruptly between shots with no in-between motion; the dropper vanishes and reappears at a different height; the liquid level changes without any drop having visibly fallen; the tube's contents jump from clear to fully cloudy within a single frame with no drop visibly causing it; or the lighting flashes, flickers, or the shadow on the tube jumps abruptly between frames with no cause.
level_2: The dropper tip jumps sideways by more than a tube-width from one drop to the next; the tube visibly rocks or rotates between frames; a patch of cloudiness appears with no drop, ripple, or gradual fade-in beforehand; the falling drops look stepped or skipped rather than continuous.
level_3: The tube stays in the same spot and upright orientation for the whole clip; the dropper holds a steady vertical position over the same point on the tube opening; the liquid surface stays calm between drops, without sloshing that isn't caused by a drop landing; each patch of new cloudiness spreads outward from where a drop hit rather than appearing everywhere in the tube at once.
level_4: Everything at the 3-point level holds, and in addition each drop's impact makes a small, brief ripple on the surface that settles down before the next drop falls; the visible size of individual precipitate flecks stays about the same relative to the tube's width from one drop to the next; the dropper tip and the tube's bottom stay fully inside the frame the whole time.
level_5: Everything at the 4-point level holds, and in addition every drop falls along a similar path toward the same spot on the liquid surface; the ripple each drop makes looks similar in size and settles at a similar pace to the others; the precipitate builds up drop by drop rather than in one sudden jump partway through; the dropper's approach and retreat between drops looks like natural hand or arm motion rather than a sudden snap into position.