Domain: Engineering — Chemical Engineering
Target concept: Concentrated sulfuric acid corrosion

Video generation prompt: Drops of sulfuric acid solutions with different concentrations (5%, 30%, and 98%) were applied onto filter paper and an iron sheet, and the resulting appearance of each material at the drop site was photographed.

Evaluation guide:
(i) Target concept: Concentration-dependent chemical reactivity of sulfuric acid, producing different responses in a cellulose substrate (dehydration) versus a metal substrate (active corrosion at lower concentrations, but passivation at very high concentration).
Minimum mechanism: Sulfuric acid must be in direct liquid contact with both the filter paper and the iron sheet; carbonization of the paper is a dehydration reaction that strengthens monotonically with concentration (strongest at 98%); the iron sheet actively corrodes, with visible gas evolution, at 5% and most visibly at 30%, but at 98% cold concentrated acid instead passivates the iron surface, so visible attack is suppressed there despite the higher concentration; no catalytic or thermal acceleration permitted.
(ii)Storyline: Frame 1–2: Static wide shot showing three labeled dropper tips above aligned substrate pairs. Frame 3–4: Simultaneous downward motion of three droplets toward respective substrate pairs; no overlap, no collision. Frame 5–6: Droplet contact with both filter paper and iron sheet per concentration; immediate wetting visible. Frame 7–8: Progressive state change onset: the 98% paper zone darkens first, the 30% zone follows, and the 5% zone stays largely unchanged; on the iron sheet, the 30% zone shows the most visible bubbling/etching, the 5% zone shows mild bubbling, and the 98% zone shows markedly less change, consistent with passivation. Frame 9–10: Final stabilized state held; all six zones fully resolved, side-by-side, fixed viewpoint, no motion.

Manual:
Experimental Procedure
1. Place three identical filter papers and three identical iron sheets side-by-side in fixed alignment.
2. Using calibrated droppers, apply one drop of 5% H₂SO₄ to first filter paper and first iron sheet; repeat for 30% (second pair) and 98% (third pair).
3. Hold view steady for observation.
Observation of Experimental Phenomena
- Filter paper: 5% → no change or faint yellowing; 30% → brown discoloration; 98% → rapid black carbonization at contact site.
- Iron sheet: 5% → mild bubbling with slow surface etching; 30% → most vigorous bubbling and visible surface roughening of the three concentrations; 98% → bubbling is markedly suppressed and the sheet stays largely intact with only mild dulling, since cold concentrated acid passivates the iron surface instead of continuing to attack it.
Summary of Experimental Principles
Concentrated H₂SO₄ dehydrates cellulose (filter paper), causing carbonization that intensifies with concentration. Its effect on iron differs: dilute-to-moderate acid (5–30%) actively corrodes iron with visible hydrogen bubbling, but cold, highly concentrated acid (98%) instead passivates the iron surface by forming a protective oxide/sulfate layer, sharply limiting further visible attack — iron corrosion therefore does not simply worsen with concentration the way paper carbonization does.

Prompt Grounding rubric:
level_1: No filter paper or iron sheet visible in the frame; no droplets are shown being applied to either material; none of the three concentration labels (5%, 30%, 98%) appear; none of the three test conditions is depicted at all.
level_2: At least one filter paper or iron sheet is present, but at least two of the following are missing: three distinct droplet application sites; a visible difference in texture between filter paper and iron sheet; all three concentration labels (5%, 30%, 98%) placed next to their droplets.
level_3: All three concentration-labeled droplets (5%, 30%, 98%) are shown applied onto both a filter paper sample and an iron sheet sample, appearing together in the same shot; each substrate is recognizable by its texture (fibrous paper vs. reflective metal); each label is legible and sits next to its droplet site.
level_4: All conditions for score 3 are met, and additionally: each concentration's droplet appears on both required substrates (the filter-paper counterpart and the iron-sheet counterpart are both present for 5%, for 30%, and for 98%), with no concentration missing either pairing.
level_5: All conditions for score 4 are met, and additionally: the six substrate-droplet units are laid out as three paired columns (5% pair, 30% pair, 98% pair), all visible at once from one fixed camera position, with no pair hidden behind another and no rotation or zoom that cuts off any pair.

Scientific and Causal Correctness rubric:
level_1: No observable change appears on either substrate at any concentration; the paper looks the same across 5%, 30%, and 98%; the iron sheet looks the same across all three; there is no distinction between the paper's dehydration response and the iron's corrosion response.
level_2: A change appears on at least one substrate, but it does not track acid behavior correctly: for example the paper's darkening does not increase with concentration, or the iron sheet shows its worst pitting/etching at 98% rather than at 30% (contradicting passivation).
level_3: The filter paper shows blackening/browning that increases from 5% to 30% to 98%, consistent with dehydration intensifying with acid strength; the iron sheet shows visible bubbling and surface etching at 5% and, more strongly, at 30%, while the 98% iron site shows markedly less bubbling and only mild dulling, reflecting that concentrated acid passivates iron rather than corroding it further.
level_4: All conditions for score 3 are met, and additionally: the paper's 98% zone is clearly the darkest of the three with no melting or open flame; the iron sheet's 30% site is visibly the most attacked of the three, while its 98% site shows a passivated, only lightly dulled surface with no fresh pitting; no red rust appears at any concentration; no droplet-evaporation ring is mistaken for a reaction product.
level_5: All conditions for score 4 are met, and additionally: the paper's 98% carbonized zone has a sharply bounded dark edge that fades progressively toward the 30% and 5% sites; the iron sheet's 30% site clearly shows more surface change than its own 98% site, visually demonstrating the passivation effect rather than a simple 'stronger acid, worse corrosion' trend; no gas bubbles appear at the 98% iron site after the initial contact; all changes stay confined to each droplet's contact zone.

Spatiotemporal Consistency rubric:
level_1: A substrate teleports between frames; a droplet appears or disappears with no dispenser visible bringing it there; a drastic, unexplained brightness jump of more than 50% occurs; the filter paper tears mid-sequence with no visible cause.
level_2: A droplet's motion toward its target substrate skips or jumps across at least 2 frame drops, causing jump-cut motion; the apparent light source seems to relocate partway through the sequence in at least 2 instances, changing where highlights fall on the metal sheet; a substrate shifts sideways with no camera pan to justify it; a droplet's path from dropper tip to surface is not continuously visible.
level_3: All six substrate zones (paper and iron sheet at each of the three concentrations) stay fixed in the same on-screen position throughout; each droplet is shown falling and landing on its target surface in one unbroken motion; the highlight on the iron sheet's metallic surface stays in a consistent place across the sequence rather than jumping around; no substrate visibly stretches or warps.
level_4: All conditions for score 3 are met, and additionally: the camera framing never pans, tilts, or zooms; all six zones keep the same size and position relative to each other for the whole video; no zone is blocked from view and then revealed with its appearance already changed off-screen.
level_5: All conditions for score 4 are met, and additionally: each droplet's fall from the dropper to the surface is a single smooth, gradually accelerating motion with no pause or reversal; the visible change at each of the six zones (paper darkening, iron dulling/bubbling) builds up gradually across the observation window rather than snapping instantly to its final look; the boundary between wetted and dry regions on both paper and iron stays sharp and does not blur or double.