Domain: Natural Science — Chemistry
Target concept: White precipitate of aromatic electrophilic substitution reaction

Video generation prompt: Add 1 mL of 0.1M phenol solution to 3 mL of 0.1M bromine water solution and observe for 5 minutes.

Evaluation guide:
Target concept: Electrophilic aromatic substitution (EAS) in activated arenes, specifically the instantaneous, stoichiometric bromination of phenol yielding insoluble 2,4,6-tribromophenol as a white precipitate. Minimum mechanistic assumptions: (i) phenol's hydroxyl group donates electrons into the aromatic ring, increasing electron density at ortho/para positions; (ii) bromine water provides Br+ electrophile via equilibrium with hypobromous acid; (iii) the tribromo product has negligible aqueous solubility due to loss of H-bonding capacity and increased molecular symmetry/hydrophobicity. Phased storyline: [Phase 1: Baseline] Clear yellow-orange bromine water (3 mL) in vial, undisturbed. [Phase 2: Causal Trigger] 1.0 mL colorless phenol solution delivered, liquid stream contacts surface. [Phase 3: Immediate Effect] Within 1-2 s: interface clouds white; orange fades visibly; turbidity spreads downward. [Phase 4: State Transition] By 5 s: suspension fully opalescent; by 30 s: precipitate grains settle; by 2 min: compact white sediment plus pale yellow supernatant. Visibility constraints: must show meniscus, color gradient, and sediment layer thickness in sharp focus; lighting must enable discrimination of white precipitate against pale yellow supernatant (no backlight washout); camera angle must be frontal/slightly oblique to capture vertical settling without parallax distortion.

Manual:
I. Basic Demonstration Information
Demonstration Title: White Precipitate Formation in Electrophilic Aromatic Substitution (Phenol Bromination)
Subject: Chemistry - Organic Chemistry - Aromatic Electrophilic Substitution
Demonstration Purpose: To visually demonstrate the rapid, quantitative formation of a white precipitate (2,4,6-tribromophenol) when phenol undergoes electrophilic bromination with bromine water — illustrating the high reactivity of activated aromatic rings and the diagnostic utility of this reaction.

II. Demonstration Carrier/Equipment
Core Carrier: 0.1 M aqueous phenol solution (colorless, stored in amber dropper/syringe); 0.1 M bromine water (distinctive yellow-orange, ~3 mL in clear glass test tube or vial, meniscus visible).
Auxiliary Equipment: Calibrated 1-mL syringe or volumetric dropper (with 0.1-1.0 mL markings); white tile or matte background for contrast; stopwatch or timer (for 5-min observation window); safety goggles and gloves (implied in professional lab context).

III. Demonstration Content Description
Layout: Place bromine water vial upright on white background. Position phenol syringe/dropper above it, aligned vertically. Ensure front-lit, glare-free illumination highlighting color and opacity changes.
State Control: Use freshly prepared reagents; bromine water must retain strong yellow-orange hue (no fading); phenol solution must be clear and odorless (no oxidation products). Avoid shaking post-addition to allow natural sedimentation.
Comparison Baseline: Contrast pre-mix state (transparent yellow-orange liquid) vs. post-mix state (opaque white suspension -> settled white precipitate + pale yellow supernatant).

IV. Observation of Core Phenomena
Initial State: Bromine water is homogenous, transparent, and vivid yellow-orange; no haze, particles, or layering.
Addition Event: 1.0 mL phenol solution delivered smoothly and completely into bromine water within ~2 s.
Immediate Change (0-3 s): Rapid onset of milky white turbidity at liquid interface, spreading uniformly; simultaneous fading of orange intensity.
Stable State (3-60 s): Dense, granular white precipitate forms and begins settling; supernatant clarifies to pale yellow or straw color.
Final State (5 min): Compact, chalky-white sediment occupies bottom 20-30% of container; supernatant is nearly colorless to faint yellow; precipitate does not redisperse upon gentle tilt.
Characteristic Stability: Precipitate remains white (no yellowing/browning), insoluble, and crystalline in appearance; no gas evolution, heat emission, or secondary color development.

V. Summary of Key Knowledge Points and Principles
Core Concept Definition: Electrophilic aromatic substitution (EAS) is a fundamental reaction where an electrophile replaces a hydrogen on an aromatic ring; phenol's -OH group strongly activates the ring (ortho/para-directing), enabling rapid polybromination under mild conditions.
Chemical Principle: Br2 in water generates electrophilic Br+ (via HOBr); with bromine water supplied at a 3:1 molar ratio to phenol (3 mL x 0.1 M Br2 vs 1 mL x 0.1 M phenol), phenol undergoes successive brominations to yield sparingly soluble 2,4,6-tribromophenol (m.p. 95C, solubility ~0.1 g/L), causing an immediate white precipitate — a hallmark diagnostic test for phenol.
Significance: This reaction exemplifies substituent effects on aromatic reactivity, the 3:1 stoichiometric requirement (3 Br per phenol), and structure-property relationships (insolubility due to symmetry and H-bond disruption).

VI. Demonstration Precautions
Reagent Purity: Bromine water must be freshly prepared (decomposes to Br-/BrO3- on standing); phenol solution must be neutral pH (acidic conditions suppress ionization, reducing activation).
Quantitative Fidelity: Syringe must deliver exactly 1.0 mL of phenol solution into exactly 3.0 mL of bromine water — visual confirmation via calibration marks and meniscus alignment.
Timing: Observe continuously for 5 minutes; record onset time of turbidity (<2 s expected), full precipitation (<=10 s), and final sedimentation (>=2 min).
Safety: Conduct in fume hood; avoid skin contact (phenol corrosive, bromine toxic/volatile); use amber glass for bromine storage.

Prompt Grounding rubric:
level_1: No recognizable lab setting; no visible phenol solution, bromine water, or containers; no addition action shown; no white precipitate at any point; the objects on screen have no chemical identity (unlabeled clear liquids only); the sequence is absent or reversed (e.g., a white solid appears before any liquids are combined).
level_2: A generic lab bench is shown, but the reagents are unlabeled or wrongly colored (e.g., 'bromine water' shown as a colorless liquid); the volumes used are clearly not close to a 1:3 phenol-to-bromine-water ratio (e.g., equal volumes of each, or bromine water in the smaller amount); the addition is not clearly directed from the phenol container into the bromine water; no white precipitate forms, or the solid that forms is yellow or brown, or a precipitate forms and quickly redissolves.
level_3: Two clear glass containers are visible in a plausible lab setup; roughly 1 part phenol solution is added to roughly 3 parts bromine water, but there is no measurement cue (no graduated markings, no visible meniscus reading) confirming the amounts; the bromine water is shown as yellow-orange and the phenol solution as colorless; the addition happens, but the technique is sloppy (poured from well above the container, no pause afterward) and the resulting white cloudiness is faint, brief, or uneven.
level_4: Both reagents are clearly identifiable (a colorless phenol solution and a yellow-orange bromine water) and are combined in an approximately 1:3 ratio by volume (e.g., roughly 1 mL added to roughly 3 mL); the addition is a controlled pour or dropwise delivery; a dense, opaque white cloudiness appears within a couple of seconds of mixing, visibly settles within about 5 seconds, and persists, with the bromine water's orange color visibly fading rather than staying strong.
level_5: Every setup detail matches: (i) a graduated dropper or syringe delivers a clearly smaller volume of colorless phenol solution into a container holding a visibly larger volume, about three times as much (roughly 1 mL into roughly 3 mL), of yellow-orange bromine water, with markings or a meniscus that make the ratio legible; (ii) both reagents are identifiable by on-screen labels or by their standard colors (orange bromine water, clear phenol solution); (iii) the addition is smooth and stops cleanly; (iv) within a couple of seconds a milky turbidity appears and a granular white precipitate begins to settle; (v) within about 5 seconds a compact white sediment occupies roughly the bottom third of the container, with the liquid above it noticeably paler than the original bromine water.

Scientific and Causal Correctness rubric:
level_1: No causal link between combining the liquids and the appearance of any solid; a white or colored solid appears before the phenol solution is added; the bromine water stays vivid orange with no change; the solid that forms is black, green, or red; nothing in the scene suggests the reaction is specific to phenol.
level_2: A precipitate forms only after mixing, but it is the wrong color (e.g., pale yellow rather than white); the bromine water only partly loses its orange color and stays visibly dark; the precipitate redissolves or turns brown as the clip continues; nothing about the scene distinguishes this from a non-specific acid-base or oxidation reaction.
level_3: A white precipitate forms and stays; the bromine water visibly fades from orange to a much paler yellow, consistent with the bromine being consumed; the mixing is clearly shown as the cause of the cloudiness, but nothing in the scene implies the specific mechanism: there is no cue (such as on-screen labeling) tying the result to phenol's aromatic ring being brominated at multiple positions rather than some other white-precipitate-forming reaction.
level_4: The visual outcome matches the expected chemistry: adding the phenol solution to the bromine water is immediately followed by a fading of the bromine water's orange color and the formation of a persistent, opaque white precipitate, consistent with phenol's activated aromatic ring reacting rapidly with bromine to give an insoluble tribrominated product; no side effects contradict this (no gas bubbles, no heating effects, no color other than white/pale yellow appearing).
level_5: The full causal picture is visually consistent and complete: (i) the white cloudiness appears essentially as soon as the phenol solution contacts the bromine water, with no unexplained delay; (ii) the precipitate looks fine and grainy rather than gelatinous or colloidal; (iii) the liquid above the settled solid ends up pale yellow rather than still strongly orange, consistent with the bromine being largely used up (matching the 3:1 bromine-to-phenol amounts combined); (iv) there is no leftover layer of unmixed orange liquid and no separate second liquid phase; (v) no competing effects (no fizzing, no visible heating, no secondary precipitate of a different color) muddy the outcome, so the single visual story (orange bromine water plus phenol solution giving a white precipitate and a much paler liquid) reads clearly as the aromatic bromination of phenol.

Spatiotemporal Consistency rubric:
level_1: The white precipitate appears before the phenol solution is added; the container changes size, shape, or orientation partway through the clip; the color of the bromine water flickers oddly (e.g., jumping between orange and an unrelated color); a hand holding the dropper appears or disappears without any motion bringing it into or out of frame; there is an abrupt jump in time (e.g., cutting straight from an empty container to a fully settled precipitate).
level_2: A hand holds the dropper but no liquid is seen leaving it; the liquids are combined but nothing visibly changes for several seconds afterward; the precipitate appears throughout the whole container at once and then vanishes; the bromine water's color fades while the precipitate simultaneously appears to lose volume, which does not add up visually; the shadow beneath the container points a different way than the rest of the lighting suggests.
level_3: The hand's motion (approaching, dispensing, withdrawing) reads clearly; the precipitate appears in the lower part of the liquid and settles downward under gravity; the lighting stays consistent; there are minor rough edges, such as a brief jitter during the pour, a short freeze partway through, or the hand's motion looking slightly mismatched with the liquid stream's speed; the precipitate's settling speed looks a bit too fast or too slow, but the direction and general behavior are right.
level_4: The pour itself looks physically natural: the hand accelerates into the pour and eases off at the end, and the liquid stream breaks into drops or flows smoothly depending on how it is dispensed; the cloudiness starts where the two liquids meet and spreads downward from there; the settling precipitate clumps and sinks gradually rather than snapping instantly to the bottom or floating; the lighting, camera angle, and container shape stay consistent throughout.
level_5: The whole sequence is physically coherent from start to finish: (i) the liquid surface, meniscus, and pour stream all behave the way a thin, water-like liquid would, with no unnatural stiffness; (ii) the white cloudiness first appears right where the phenol solution enters the bromine water, then spreads outward and settles at a gradual, steady pace that looks physically plausible rather than instant or suspended indefinitely; (iii) the container's shape, the liquid's curved surface, and the settling sediment layer all stay geometrically consistent with each other as the camera holds its position; (iv) reflections and highlights on the glass and the cloudy liquid change believably as the precipitate forms; (v) there is no stutter, frozen frame, or abrupt jump anywhere in the clip: the pour, the clouding, and the settling all flow as one continuous, physically grounded sequence.