Domain: Natural Science — Chemistry
Target concept: Dehydration of Ethanol

Video generation prompt: Mix ethanol and concentrated sulfuric acid in a test tube, heat to 170°C using an alcohol lamp, and pass the resulting gas into bromine water.

Evaluation guide:
Target concept: Acid-catalyzed β-elimination of ethanol yielding gaseous ethene, verified by stereospecific electrophilic addition to bromine water. Minimum mechanistic assumptions: (1) conc. H₂SO₄ protonates OH group, enabling H₂O departure; (2) adjacent C–H bond deprotonation forms C=C at 170°C; (3) ethene is insoluble, less dense than air, and reacts instantly with Br₂(aq) to form colorless dibromoethane. Phased storyline: (Phase 1) Ethanol + conc. H₂SO₄ mixed in test tube → no immediate change; (Phase 2) Alcohol lamp ignited → flame heats tube base → gradual warming → visible reflux/vapor haze at ~150°C; (Phase 3) At ~170°C → steady stream of small bubbles emerges from delivery tube → first bubble bursts in bromine water → localized color fade at interface; (Phase 4) Fade spreads radially → full decolorization completed within 4 s → solution remains clear and colorless. Visibility constraints: Must show *simultaneous* presence of flame, reaction tube, delivery tube, and bromine water in one unoccluded frame; color change must be macroscopically unambiguous (reddish-brown → colorless, not pale yellow); no human hands in final 8 s to avoid occlusion during critical verification phase.

Manual:
I. Basic Demonstration Information
Demonstration Title: Dehydration of Ethanol to Ethene and Bromine Water Test
Subject: Chemistry - Organic Chemistry - Reaction Mechanisms
Demonstration Purpose: To visually demonstrate acid-catalyzed dehydration of ethanol at 170°C to produce ethene, confirmed by decolorization of bromine water via electrophilic addition; to reinforce understanding of temperature-dependent elimination vs. substitution pathways; and to master observation of gas evolution and characteristic color-change verification.
II. Demonstration Carrier/Equipment
Core Carrier: Absolute ethanol (≥99.5%), concentrated sulfuric acid (95–98%), aqueous bromine water (saturated Br₂ in water, reddish-brown), dry test tube (15×150 mm), one-hole rubber stopper with glass delivery tube (6 mm OD, 20 cm long), alcohol lamp (with methanol or ethanol fuel), iron clamp/stand, heat-resistant mat.
III. Demonstration Content Description
Layout: Clamp test tube at 45° angle over alcohol lamp. Add 2 mL ethanol, then carefully layer 1 mL conc. H₂SO₄ down wall (avoiding splashing). Insert stopper with delivery tube; immerse tube tip 1 cm into bromine water in second test tube. Ignite lamp; heat lower third of reaction tube steadily until gentle reflux appears (~170°C), then maintain.
State Control: Ensure no water contamination (prevents ether formation); avoid overheating (>180°C causes charring/SO₂); bromine water must be freshly prepared (no fading prior to gas contact).
IV. Observation of Core Phenomena
Gas Evolution: After ~10 s heating, small, uniform, colorless bubbles emerge steadily from delivery tube tip into bromine water — no fog, no odor (SO₂ absent), no soot.
Bromine Water Response: Initial reddish-brown color fades *only where gas contacts*, spreading radially to full decolorization (colorless, transparent solution) within 3–4 s of continuous bubbling — no turbidity, no precipitate.
Thermal Specificity: No decolorization occurs if heated to 140°C (ether forms, no alkene); charring (black residue) may appear in tube if overheated — confirms correct 170°C regime.
V. Summary of Key Knowledge Points and Principles
Core Concept: Ethanol undergoes acid-catalyzed E2 elimination under high-temperature conditions: H₂SO₄ first protonates the hydroxyl group, and then — in a single concerted step, without forming a discrete carbocation intermediate (a primary carbocation on ethanol would be far too unstable) — an adjacent C–H bond breaks as the protonated water leaves, generating the C=C double bond: CH₃CH₂OH →[H⁺, 170°C]→ CH₂=CH₂ + H₂O. Ethene adds Br₂ across the C=C bond: CH₂=CH₂ + Br₂ → BrCH₂CH₂Br (colorless), causing quantitative decolorization.
Why 170°C?: Below 140°C → intermolecular dehydration → diethyl ether; 170°C favors intramolecular elimination → ethene. Conc. H₂SO₄ acts as catalyst and dehydrating agent.
Verification Logic: Bromine water decolorization is *specific* to unsaturation (C=C or C≡C); saturated compounds (e.g., ethane, ether) cause no change. Color loss is rapid, complete, and irreversible — distinguishing it from reduction (SO₂ gives white ppt) or dilution (leaves turbidity).

Prompt Grounding rubric:
level_1: No test tube, alcohol lamp, or bromine water container appears in the frame; ethanol and concentrated sulfuric acid are never shown being combined, or a different liquid entirely stands in for one of them (e.g., plain water instead of the acid); there is no delivery tube connecting the reaction vessel to the bromine water; the whole setup bears no resemblance to the mixing/heating/gas-collection sequence in the prompt.
level_2: Some correct pieces of equipment appear (a test tube, an alcohol lamp), but the setup breaks in an important way: ethanol and concentrated sulfuric acid are never visibly combined in the same test tube; the heat source is an electric hot plate or a Bunsen burner rather than an alcohol lamp; the bromine water container is missing or holds an obviously clear liquid instead; the delivery tube is absent or clearly disconnected; or the order is wrong, e.g. the bromine water is shown before any heating begins.
level_3: All the core pieces are present (a test tube holding liquid, an alcohol lamp underneath it, a separate container of bromine water, and a tube connecting them), but a key detail is off: the delivery tube's end is not actually inside the bromine water (so no bubbling could occur), the bromine water looks colorless rather than reddish-brown, the ethanol and acid are added without any visible sign that they were combined, or heating is shown with no cue (steam, condensation on the tube walls) that the mixture is actually getting hot.
level_4: Every core object is correctly placed and connected: ethanol and concentrated sulfuric acid are visibly combined in one test tube, the alcohol lamp heats its lower section, and the delivery tube runs from the stopper into the bromine water; the bromine water starts out reddish-brown as expected; the only shortcomings are minor, such as no visible steam or haze rising from the heated tube, no hint of the bromine water beginning to change, or a missing label confirming which bottle holds the concentrated acid.
level_5: The setup matches the prompt in every visible detail: a test tube holds about 2 mL of colorless ethanol topped with roughly 1 mL of a slightly denser, faintly yellow-tinted layer of concentrated sulfuric acid, added without violent mixing; an alcohol lamp with a steady blue flame sits under the lower third of the tube; a glass delivery tube runs from the stopper down into a second container of clearly reddish-brown bromine water; and the sequence plays out in the right order (mixing, then lighting the lamp, then sustained heating, then gas flowing into the bromine water), all captured within one continuous, unobstructed view.

Scientific and Causal Correctness rubric:
level_1: Nothing scientifically meaningful happens: the bromine water stays deep reddish-brown the whole time with no fading, no gas bubbles ever appear, and there is no visible connection between the heating and any change in the bromine water; or the setup shows an obviously wrong product (e.g., a gas behaving like CO2 or H2 rather than a hydrocarbon reacting with bromine water), or the ethanol appears to boil or decompose at room temperature with no acid involved.
level_2: The bromine water does change color, but for the wrong reason: dilution, evaporation, or someone stirring it rather than any gas reacting with it; bubbles appear but seem to have no effect on the bromine water; heating is shown but produces no vapor or haze above the liquid; or the video implies the gas is just steam or alcohol vapor rather than a genuine reaction product, with no sense that reaching a high enough temperature (around 170°C, well above the ether-forming range) matters.
level_3: The causal picture is partly right: bubbles reach the bromine water and the color starts to fade at the point of contact, but full decolorization never completes; the heating shown looks too brief (well under 5 seconds) to plausibly reach the ~170°C needed for the reaction; there's no sign of the expected side effect of concentrated sulfuric acid at high heat (some darkening/charring of the tube's contents); and nothing in the video other than context implies the gas is a genuine alkene rather than some other product.
level_4: The causal story holds together: a steady stream of small, evenly sized bubbles begins only once heating has clearly continued for roughly 8–10 seconds; the bromine water fades from reddish-brown through pale yellow to nearly colorless in a way that spreads outward from where the bubbles enter, consistent with a chemical reaction rather than simple mixing; the liquid in the test tube shows a hint of darkening consistent with prolonged exposure to hot concentrated acid; and there is no sign of a competing process (such as a sweet smell or different-looking vapor suggesting ether formation instead).
level_5: The full causal chain is visually supported: a faint haze or gentle simmering appears above the liquid before any bubbles are seen, gas evolution starts only after that thermal buildup, and the bubbles are small and rise at a steady, unhurried pace consistent with a light gas passing through liquid; the bromine water undergoes a complete, one-way fade from reddish-brown to fully colorless and clear within 3–4 seconds of sustained bubbling, in a way that reads as a genuine reaction rather than dilution (which would leave the liquid hazy) or a different kind of reduction (which would leave a solid residue behind); nothing in the scene suggests the milder, lower-temperature ether-forming pathway is occurring instead of the alkene-forming one.

Spatiotemporal Consistency rubric:
level_1: The scene breaks down spatially or temporally: the test tube and the bromine water appear in visually disconnected shots with mismatched backgrounds or lighting; the flame appears or vanishes abruptly mid-sequence; the bromine water starts fading before any gas has actually reached it; a hand inserts the delivery tube only after the bromine water has already gone colorless; or there are large, unexplained jumps in time or objects that suddenly change size or float unnaturally.
level_2: Noticeable breaks remain: the delivery tube bends at a sharp angle with nothing supporting it; the bromine water container looks smaller than the test tube yet sits higher up, which doesn't match how the setup should be arranged; the flame flickers in an unnatural, jumpy way; gas bubbles appear to sink or stall inside the liquid instead of rising; or heating appears to start only after gas is already bubbling into the bromine water.
level_3: The scene is mostly consistent, with small slips: a slight shift in the relative position of the test tube and bromine water container between shots; the flame's height changing noticeably without any visible reason; bubble sizes varying a lot from one to the next in a way that looks uneven rather than steady; or the bromine water beginning to fade a little before the first bubble visibly reaches the bottom of the container.
level_4: The scene holds together well: the camera stays at the same angle throughout, and the flame's glow keeps illuminating the test tube and delivery tube from the same side without any sudden shift in brightness or shadow position; the delivery tube follows a natural, unkinked curve into the bromine water; the flame stays a steady size and color; the bubbles are fairly uniform in size and rise at an even, unhurried pace; and the sequence of first bubble reaching the bromine water, followed shortly by the first visible fading at that spot, followed by the fade spreading outward, all happens in a believable, connected order.
level_5: Everything holds together as one continuous, physically believable scene: the camera holds one fixed angle for the whole clip, and the alcohol lamp's flame keeps casting the same soft glow and shadow beneath the test tube from start to finish, with no unexplained brightening, dimming, or shift in where the shadows fall; the test tube is clamped at an angle with the lamp beneath it, and the delivery tube curves smoothly down into the bromine water without any support gaps or occlusion; the flame burns steadily with a calm blue cone; gas evolution starts as a few slow, separate bubbles and smoothly builds into a steady stream; and the bromine water's color fade begins right at the point where the first bubble bursts and spreads outward at a steady, unhurried pace until the whole container looks uniformly clear, with no splashing, streaking, or color rebound anywhere in the shot.