Domain: Natural Science — Chemistry
Target concept: Carboxyl group reacts with sodium

Video generation prompt: A test tube contains an appropriate amount of glacial acetic acid. A small amount of sodium metal solid is added to the test tube.

Evaluation guide:
(i) Target concept: Visual demonstration of sodium metal reacting with the acidic O–H proton of a carboxylic acid (acetic acid's -COOH group), releasing hydrogen gas.
Minimum mechanism: Sodium (density ≈0.97 g/cm³) is less dense than glacial acetic acid (density ≈1.05 g/cm³), so it floats and moves across the liquid surface rather than sinking; the acetic acid must be anhydrous (glacial) to keep the reaction at a moderate, filmable vigor: any water present would also react with sodium and sharply increase the vigor, confounding the carboxyl-group demonstration; the carboxyl proton is far more acidic than an alcohol's hydroxyl proton, so hydrogen gas is released quickly and continuously; hydrogen is insoluble and rises as bubbles; sodium stays solid metal, shrinking as it reacts, until fully consumed.
(ii)Storyline: [Frame 1–2] Static shot of an upright test tube containing clear liquid (acetic acid), meniscus visible. [Frame 3–4] A piece of sodium enters frame from above, descending toward the liquid surface. [Frame 5] Sodium touches the surface and floats there rather than sinking; vigorous bubble formation begins immediately at the contact point. [Frame 6–9] Sodium moves erratically across the surface while a rapid, continuous stream of bubbles rises around it, shrinking steadily but keeping its metallic shine. [Frame 10] Sodium is fully consumed at or near the surface; the last bubbles reach the top. Perspective: fixed frontal close-up, centered on the test tube, full visibility of the sodium, the bubble stream, and the liquid column throughout.

Manual:
Experimental Procedure
1. A transparent test tube contains a colorless liquid (glacial acetic acid) filling about 1/3 of its height.
2. A small piece of silvery-white sodium metal is added from above into the test tube.
Observation of Experimental Phenomena
- Sodium floats at the liquid surface (it is less dense than acetic acid) and immediately begins vigorous, rapid effervescence.
- A fast stream of small, colorless bubbles forms around the sodium as it moves across the surface.
- Sodium shrinks steadily but keeps its metallic shine until it is fully consumed at the surface.
- The liquid remains colorless and clear throughout; no flame or explosion occurs at this scale.
Summary of Experimental Principles
Acetic acid (CH3COOH) contains a carboxyl group (-COOH) whose O-H proton is considerably more acidic than the O-H proton of an alcohol such as ethanol. Sodium reacts with this acidic proton to release hydrogen gas and form sodium acetate: 2CH3COOH + 2Na → 2CH3COONa + H2. Because the carboxyl proton is so much more acidic, this reaction is visibly faster and more vigorous than the analogous reaction between sodium and ethanol — directly illustrating why a carboxyl group reacts with sodium more readily than a hydroxyl group.

Prompt Grounding rubric:
level_1: No test tube appears; no clear liquid representing acetic acid is shown; no sodium metal solid is shown; no addition action takes place; none of the three required elements (test tube, acetic acid, sodium) appear.
level_2: Only one of the three required elements appears (test tube alone, or the liquid alone, or the sodium alone); or two appear but are the wrong type (e.g., a beaker instead of a test tube, water instead of acetic acid, a piece of chalk instead of sodium); no addition action is shown.
level_3: A transparent test tube containing a colorless liquid (acetic acid) is shown, along with a small silvery-white metallic solid (sodium); the sodium is shown moving from outside the frame into the test tube, but the timing is off (for example, the sodium appears already inside the tube with no visible entry, or the tube appears to be empty right before the sodium arrives).
level_4: The test tube, the colorless acetic acid, and the sodium are all present and correctly identified; the sodium is shown moving continuously into the test tube from above; the liquid is already in the tube before the sodium enters; the tube stays upright and in place; no object is duplicated, swapped out, or appears out of nowhere.
level_5: Everything required for score 4 holds, and in addition the sodium enters the tube in one unbroken motion with no pause or flicker, the tube keeps the same upright position and place in the frame throughout, the liquid surface stays undisturbed until the sodium actually touches it, and there is no visible break in the outline, transparency, or metallic sheen of either object.

Scientific and Causal Correctness rubric:
level_1: No plausible reaction is shown at all: nothing changes after the sodium enters the liquid, the liquid changes color (blue, green, red), a flame or explosion appears, or the sodium disappears without any trace of gas.
level_2: The reaction shown doesn't match sodium reacting with a carboxylic acid: for example the sodium sinks to the bottom and reacts as slowly and gently as it would in an alcohol, no bubbles appear at all, the sodium dissolves away with no visible gas, or the released gas is drawn as colored smoke or liquid droplets rather than bubbles.
level_3: The sodium floats at or near the liquid surface rather than sinking to the bottom, and a rapid, continuous stream of small, colorless bubbles forms as soon as it touches the liquid; the sodium stays visibly metallic (silvery-white) while this is happening; no flame, melting, or discoloration of the sodium appears; the liquid itself stays colorless and clear.
level_4: Everything required for score 3 holds, and in addition the bubbling is clearly more vigorous than a slow, gentle fizz (the sodium visibly moves or darts around on the surface as gas is released), no bubbles form before the sodium makes contact, and bubble production doesn't stop before the sodium is fully used up.
level_5: Everything required for score 4 holds, and in addition the bubbling stays vigorous and roughly steady until the sodium is gone, the bubbles are consistently small and rise quickly to the surface, the rate at which the sodium shrinks matches the intensity of the bubbling, and nothing in the scene hints at a gas other than hydrogen (no visible condensation, colored haze, or heat shimmer).

Spatiotemporal Consistency rubric:
level_1: The test tube vanishes and reappears, the sodium jumps to a new spot with no path shown getting there, the liquid level changes with no matching cause, the lighting flips abruptly between frames, the camera angle rotates sharply (more than about 15°) mid-clip, or an object flickers in and out of existence.
level_2: The test tube tilts or wobbles violently (more than about 30°), the sodium's motion strobes or repeats, the liquid surface ripples for no reason, the tube's shadow suddenly points a different way, or background elements move independently of the tube in ways that don't match the camera.
level_3: The test tube stays upright and in the same spot; the sodium moves in a visually coherent way across or into the liquid; the liquid surface only distorts where the sodium is actively disturbing it and settles back down naturally elsewhere; the tube's shadow keeps a steady direction and softness; nothing clips through the glass, warps oddly, or shows jagged edges.
level_4: Everything required for score 3 holds, and in addition the sodium's movement on or near the surface looks physically reasonable (it doesn't move faster than the bubbling around it would suggest), the bubbles visibly speed up as they near the surface, the sodium never appears to pass through the tube wall, and gas bubbles never appear before the sodium has entered the liquid.
level_5: Everything required for score 4 holds, and in addition the test tube shows no visible shake or drift in its position for the whole clip, the bubble paths look essentially straight up rather than veering sideways, any distortion of the sodium's shape stays limited to where it's actually touching the liquid and spreads outward naturally from there, and there is no frame doubling or ghosting that makes it hard to tell what's the sodium and what's a bubble.