Domain: Natural Science — Chemistry
Target concept: Acid-base neutralization reaction under excess acid conditions, accompanied by visible decolorization of the indicator.

Video generation prompt: Two transparent beakers contain acidic solutions with phenolphthalein; a small amount of sodium hydroxide is added to the left one, and a larger amount is added to the right one, followed by shaking and mixing.

Evaluation guide:
(i) Target concept: Visual demonstration that adding an insufficient amount of NaOH to an excess-acid, phenolphthalein-containing solution produces only a brief, localized pink flash that decolorizes back to colorless once mixed throughout the beaker, whereas adding enough NaOH to neutralize (and slightly exceed) the acid produces a pink color that persists uniformly after mixing.
Minimum mechanism: Phenolphthalein is colorless below bulk pH ~8.2 and pink above it; a droplet of NaOH momentarily raises the pH right where it lands, producing a local pink flash; if the total NaOH added is not enough to neutralize all the acid present, shaking redistributes the base and the bulk solution settles back below pH ~8.2, so the flash fades to colorless; if the total NaOH exceeds the acid present, shaking raises the bulk pH above ~8.2 and the pink persists evenly throughout the beaker.
(ii)Storyline: Frame 0–1: Static side-by-side view of two beakers with identical colorless liquid (acidic solution with phenolphthalein). Frame 2–3: A small amount of NaOH is added to the left beaker → a brief pink flash appears where it lands → as shaking mixes it through the beaker, the color fades back to colorless (the acid remains in excess overall). Frame 4–5: A larger amount of NaOH is added to the right beaker → pink appears and, as shaking mixes it through, spreads into a uniform, lasting pink across the whole beaker (the base is now in excess). Throughout: fixed viewpoint, no occlusion, full visibility of both beakers and their color states; the causal order stays intact: addition always precedes any color change, mixing determines whether that color fades or persists, and the contrast between the two beakers only becomes clear once both have finished being shaken.

Manual:
Experimental Procedure
1. Place two identical transparent beakers side-by-side.
2. Fill both with colorless acidic solution containing phenolphthalein indicator.
3. Add a small amount of sodium hydroxide solution to the left beaker.
4. Add a larger amount of sodium hydroxide solution to the right beaker.
5. Shake and mix the contents of both beakers separately.
Observation of Experimental Phenomena
- Left beaker: a brief pink flash appears where the NaOH lands, then fades back to colorless as shaking mixes it through the beaker (acid remains in excess overall).
- Right beaker: pink appears and becomes uniform and persistent as shaking distributes it, because enough base was added to neutralize the acid and leave a slight excess.
- No color appears in either beaker before its NaOH is added.
Summary of Experimental Principles
Phenolphthalein is colorless below bulk pH ~8.2 and pink above it. Adding a small amount of NaOH can locally and briefly raise the pH above this threshold at the point of contact, producing a flash of color, but if the total base is insufficient to neutralize all the acid present, mixing lowers the bulk pH back below the threshold and the color fades. Adding a larger amount of NaOH supplies enough base to neutralize the acid and leave a base excess, so the pink persists uniformly once mixed.

Prompt Grounding rubric:
level_1: Neither transparent beaker is shown; no colorless acidic phenolphthalein solution appears in either beaker; no sodium hydroxide is added to either beaker; the two beakers aren't distinguished as left and right; no shaking or mixing action occurs.
level_2: Two transparent beakers appear but are not arranged side by side; at least one beaker already holds a colored liquid instead of the colorless acidic solution; sodium hydroxide is added to only one beaker, or added in visually identical amounts to both; there's no visible difference between a small and a larger addition; neither beaker is shown being shaken or mixed.
level_3: Two transparent beakers sit side by side in the same shot from a fixed viewpoint; both start with the same colorless liquid; sodium hydroxide is added to the left beaker and, separately, to the right beaker, with the left addition happening first; at least one of the two beakers is shown being shaken or mixed afterward.
level_4: Everything at the 3-point level is present, and in addition, the amount of NaOH added to the left beaker is visibly smaller than what's added to the right beaker (e.g., a single drop versus a longer pour or several drops); both beakers are shown being shaken or mixed, not just one; the whole sequence plays out in one continuous shot without cutting away or repositioning the camera.
level_5: Everything at the 4-point level is present, and in addition, the two beakers are aligned at the same height, spacing, and orientation throughout; the small addition to the left beaker reads as clearly minimal (e.g., a single droplet touching the surface), while the larger addition to the right beaker reads as clearly greater (e.g., three or more droplets or a brief sustained stream); the shaking of both beakers happens with matching motion and duration, so the two mixing actions look like fair, comparable trials.

Scientific and Causal Correctness rubric:
level_1: Neither beaker changes color at any point, or both beakers turn pink identically regardless of how much NaOH was added, or a color appears before any NaOH is added, or the colors shown don't match phenolphthalein's acid-base behavior at all (e.g., a color other than pink appears).
level_2: A color change happens, but it doesn't follow from the amounts added: e.g., color appears before the NaOH touches the liquid, or the left beaker (which received less base) ends up more strongly and permanently pink than the right beaker, or the color shown isn't a shade of pink (e.g., blue, yellow, or purple appears instead).
level_3: Color appears only after NaOH is added and only in the beaker(s) that received it; in the left beaker (small NaOH addition), any pink that appears where the drop lands fades back to colorless as shaking mixes it through the beaker, leaving the bulk solution colorless because the added base is not enough to overcome the acid present; in the right beaker (larger NaOH addition), the pink persists and becomes uniform through the whole beaker once mixed, because the base added is enough to neutralize the acid and leave a slight excess; no color appears in either beaker before its own NaOH addition.
level_4: Everything at the 3-point level is present, and in addition, the left beaker's fading color reads clearly as returning to fully colorless rather than settling into a faint permanent pink, while the right beaker's pink reads as fully and evenly developed once mixed; the color changes stay confined to each beaker's own liquid (no bleeding between beakers, no coloring of the beaker walls); the right beaker shows no lingering colorless streaks once mixing is complete.
level_5: Everything at the 4-point level is present, and in addition, the contrast between the two beakers is unambiguous by the end of the video: the left beaker is visibly back to fully colorless while the right beaker is a saturated, vivid pink; at no point does either beaker show an intermediate or ambiguous hue (no lavender, no orange-tinted pink); once each beaker reaches its final state, that state (colorless for left, pink for right) holds steady with no further fading or darkening.

Spatiotemporal Consistency rubric:
level_1: One or both beakers suddenly appear in a different spot or at a different size with no motion shown getting there; the liquid level or its surface shape jumps instantly between two frames; the shaking motion starts or stops with no ramp-up or slow-down at all, as if switched on and off; the room's lighting swaps dramatically partway through for no visible reason; a beaker's shape changes (e.g., a cylindrical beaker becomes cone-shaped).
level_2: The beakers stay in place but show a visible glitch: one flickers partially out of view, its transparency looks inconsistent from frame to frame, or a faint duplicate outline trails behind it; the liquid behaves impossibly (e.g., instantly becomes uniformly mixed with no visible swirling during shaking, or shows ripples while sitting still); a shadow on a beaker or the bench suddenly points a different direction or changes strength with no corresponding change in any light source shown.
level_3: Both beakers stay put, keep their shape, and stay transparent throughout; each liquid surface reacts believably, rippling briefly where a drop lands, then swirling and deforming naturally while its beaker is shaken; the direction and brightness of the light in the scene looks the same from one moment to the next; nothing about either beaker or its contents jumps or cuts unexpectedly.
level_4: Everything at the 3-point level is present, and in addition, each NaOH drop falls in a smooth vertical path and appears to slow naturally as it nears the surface rather than snapping into place; the shaking motion carries a bit of natural momentum (the liquid keeps swirling briefly just after the hand stops moving the beaker); neither beaker flickers, tears, or visibly warps at any point; the color mixing in spreads gradually rather than turning the whole beaker one shade all at once.
level_5: Everything at the 4-point level is present, and in addition, every visible motion lines up in time with its cause: a drop's impact matches the ripple it produces, and shaking in each beaker only begins once that beaker's addition is finished; the two beakers' shaking motions look similar to each other in rhythm and timing; no part of either beaker's footage looks noticeably shakier, blurrier, or more out-of-focus than the rest, in a way that would make it look stitched from different footage.