Domain: Natural Science — Chemistry
Target concept: 2,4-Dinitrophenylhydrazine reacts with carbonyl groups to form a solid precipitate.

Video generation prompt: Two transparent glass vials are placed side by side: an appropriate amount of acetaldehyde is added to the left one, and an appropriate amount of ethanol is added to the right one. Then, 2,4-dinitrophenylhydrazine is added to both, and the mixtures are gently shaken.

Evaluation guide:
(i) Target concept: Selective precipitation assay for carbonyl functional group identification via 2,4-DNPH derivatization.
Minimum mechanism: Acetaldehyde must contain a reactive aldehyde carbonyl; ethanol must be carbonyl-free; 2,4-DNPH must be in solution and chemically intact; reaction requires molecular contact and mild agitation to initiate nucleophilic addition-elimination; precipitate formation is irreversible and visually distinct due to the hydrazone chromophore.
(ii)Storyline: Frame opens on static overhead/frontal view showing two identical transparent glass vials aligned horizontally. Left vial receives clear liquid labeled/identified as acetaldehyde; right vial receives clear liquid labeled/identified as ethanol. Then, identical amber-colored 2,4-DNPH solution is dispensed into both vials simultaneously. Both vials are then shaken with identical oscillatory motion. After shaking ceases, left vial develops a yellow granular solid precipitate that settles or remains suspended; right vial shows zero change: remains optically clear and homogeneous. Entire sequence occurs from fixed viewpoint with no cuts, no object insertion/removal, and no lighting shift.

Manual:
Experimental Procedure
1. Place two transparent glass vials side-by-side.
2. Add acetaldehyde to left vial; add ethanol to right vial.
3. Add 2,4-dinitrophenylhydrazine solution to both vials.
4. Gently shake both vials.
Observation of Experimental Phenomena
Yellow granular precipitate forms only in left vial (acetaldehyde); right vial (ethanol) remains clear and transparent with no precipitate.
Summary of Experimental Principles
2,4-Dinitrophenylhydrazine reacts selectively with carbonyl groups (e.g., the aldehyde in acetaldehyde) to form an insoluble yellow 2,4-dinitrophenylhydrazone precipitate; ethanol lacks a carbonyl group and thus shows no reaction.

Prompt Grounding rubric:
level_1: Fewer than two vials appear, or the two vials are not shown side by side, or no clear liquid is added to the left vial to represent the acetaldehyde, or no clear liquid is added to the right vial to represent the ethanol, or the 2,4-DNPH solution is never added to either vial, or neither vial is ever shaken.
level_2: Both vials are present side by side, but at least one setup step is missing: the acetaldehyde is not added to the left vial, the ethanol is not added to the right vial, the 2,4-DNPH solution is added to only one vial instead of both, or the shaking step is skipped for one or both vials.
level_3: Both vials sit side by side with acetaldehyde in the left one and ethanol in the right one; the same amber 2,4-DNPH solution is added to both vials; both vials are then shaken; every object and action named in the prompt is present and correctly matched to the left/right vial.
level_4: All of score 3, plus: both vials stay fully visible and in place for the whole clip, nothing (extra containers, a hand, other reagents) blocks the view of either vial while reagents are added or during shaking, and it stays visually clear throughout which vial is left (acetaldehyde) and which is right (ethanol).
level_5: All of score 4, plus: the acetaldehyde and ethanol are added before the 2,4-DNPH, the 2,4-DNPH is added to both vials at essentially the same moment with a matching pour, the shaking happens only after all reagents are added and looks the same for both vials (same length, same vigor, same motion), and the whole sequence plays out as one continuous shot with no cut, zoom, or repositioning.

Scientific and Causal Correctness rubric:
level_1: No precipitate forms in either vial, or a precipitate forms in the ethanol (right) vial, or a precipitate appears before the 2,4-DNPH is added, or both vials end up looking the same, or the solid that forms is blue, green, or orange-red rather than yellow.
level_2: A precipitate forms in only one vial but it's the wrong one (the ethanol/right vial instead of the acetaldehyde/left vial), or both vials show a precipitate with no visible difference between them, or the solid that forms is white, gray, or brown rather than a yellow, granular solid.
level_3: A precipitate forms only in the left (acetaldehyde) vial and not in the right (ethanol) vial; the precipitate is yellow and has a granular, solid appearance: the correct differential result based on which liquid actually contains a carbonyl group.
level_4: All of score 3, plus: the precipitate only becomes visible once the shaking has finished (not during or before it), it stays put in the left vial without dissolving back into the liquid or disappearing, and the right vial stays completely clear and liquid with no haze or particles.
level_5: All of score 4, plus: the right vial shows absolutely no particles, haze, or off-color tinge, the left vial's precipitate is unambiguously yellow (not orange, not brown, not white), the solid clearly looks like a granular precipitate rather than an oily film or needle-like crystals, and nothing about the lighting or reflections in either vial creates the false impression of a precipitate that isn't really there.

Spatiotemporal Consistency rubric:
level_1: A vial disappears and reappears in a different spot, a vial suddenly changes size or shape, the lighting or shadows shift abruptly for no reason tied to the reaction, a vial's glass appears to bend or distort unnaturally, or the shaking causes a vial to crack, leak, or fly out of frame.
level_2: The two vials are no longer side by side partway through the clip, a hand reaches in to add a reagent and then vanishes without ever leaving the frame, the shaking starts or stops with a sudden jolt rather than easing in or out, or a vial's contents change appearance instantly with no visible transition.
level_3: Neither vial disappears or breaks, nothing moves in a physically impossible way, the two vials stay side by side the whole time, the shaking looks like a natural back-and-forth motion with a believable range, and the liquid surfaces respond naturally to the shaking (the meniscus shifts, small ripples appear).
level_4: All of score 3, plus: neither vial's transparency flickers or strobes, no unnatural blur hides which vial the precipitate is forming in, both vials stay equally in focus at all times, and no droplet of reagent is left hanging unsupported in the air after being added.
level_5: All of score 3 and score 4, plus: the shaking motion never pauses or jumps between cycles, the liquid surface in each vial rises and falls smoothly in a way that matches how a real liquid would slosh, the rims and bases of both vials stay aligned frame to frame with no visible misregistration, and the moving liquid surface never appears to freeze or stutter between frames.