Domain: Natural Science — Chemistry
Target concept: Evaporation Rate Comparison: Ethanol and Ether Droplets on a Glass Surface

Video generation prompt: Place identical droplets on a clean glass plate: the left one is ethanol and the right one is ether, exposed to quiescent air.

Evaluation guide:
Target concept: Differential evaporation kinetics driven by intermolecular forces, specifically, hydrogen bonding suppression of volatility in ethanol versus minimal intermolecular restriction in ether. Minimum mechanistic assumptions: (i) identical initial conditions (volume, substrate, T/RH, air quiescence); (ii) liquids are pure and non-reactive with glass; (iii) evaporation is surface-controlled and diffusion-limited under still air. Phased storyline: [t=0] Two identical clear droplets deposited side-by-side on clean glass; [t=1–3 s] Ether droplet visibly contracts faster, diameter shrinking at ~2.5× ethanol’s rate; [t=5–7 s] Ether fully vanished; [t=7–10 s] Ethanol remains clearly visible (>30% original size), with smooth, uninterrupted recession. Visibility constraints: Must be side-on or top-down orthogonal view (no oblique angles distorting relative size); lighting must avoid specular glare on droplets; labels must be externally affixed and unambiguous; no human presence during observation phase.

Manual:
I. Basic Demonstration Information
Demonstration Title: Evaporation Rate Comparison: Ethanol and Ether Droplets on a Glass Surface
Subject: Natural Science - Chemistry - Physical Properties of Liquids
Demonstration Purpose: By placing identical volumes of ethanol (left) and diethyl ether (right) on a clean glass plate under still air, this demonstration visually compares their relative evaporation rates; it illustrates how intermolecular forces (hydrogen bonding in ethanol vs. weak dipole-dipole interactions in ether) govern volatility; and it trains learners to recognize kinetic differences through direct side-by-side temporal observation.

II. Demonstration Carrier/Equipment
Core Carrier: Pure anhydrous ethanol (≥99.5%), pure diethyl ether (≥99.0%), clean microscope glass slide (76×26 mm, soda-lime, chemically cleaned with acetone then air-dried)
Auxiliary Equipment: Digital micropipette (10 µL calibrated), precision tweezers, static-air enclosure (transparent acrylic box, no ventilation), LED diffuser panel (5500K), side-view fixed-focus camera (1080p, 60 fps), waterproof labels ('Ethanol' blue, 'Ether' yellow)

III. Demonstration Content Description
Layout: Place glass slide horizontally on vibration-isolated surface inside static-air enclosure. Using micropipette, deposit one 10 µL liquid sample at center-left (x = 20 mm) and one 10 µL sample at center-right (x = 56 mm) — ensuring ≥30 mm separation. Affix labels externally: 'Ethanol' aligned left edge, 'Ether' aligned right edge.
State Control: Perform at 25±1°C, 50±5% RH; allow 5 s equilibration post-deposition (for the liquid to settle into its spread footprint) before recording. No airflow, no handling during recording.
Comparison Baseline: Identical volume, identical substrate, identical ambient conditions — isolating only chemical identity as variable.

IV. Observation of Core Phenomena
Ether Pool Behavior: Rapid, smooth, steady shrinking of its spread footprint; visible reduction within the first 2 s; complete disappearance by 7-8 s; edge stays roughly rounded and well-defined until the final, smallest stage.
Ethanol Pool Behavior: Gradual, slower shrinking; retains more than half its initial footprint at 8 s; its edge recedes steadily but visibly persists well beyond ether's endpoint.
Characteristic Stability: Both liquids wet the clean glass and spread out into thin, shallow pools rather than beading up, consistent with their low surface tension; each pool's edge recedes steadily as it evaporates, with no bubbling, clouding, or residue — confirming purity and a clean surface.
Auxiliary Comparison: Side-by-side placement enables direct visual ratio estimation (e.g., 'ether has lost half its area while ethanol has lost only about 15%'), reinforcing quantitative intuition about relative volatility.

V. Summary of Key Knowledge Points and Principles
Core Concept Definition: Evaporation rate is the mass (or volume) loss per unit time from a liquid's exposed surface as molecules overcome intermolecular attraction and enter the vapor phase; it depends critically on vapor pressure, temperature, exposed surface area, and intermolecular force strength.
Scientific Principle: Diethyl ether (bp 34.6°C, no hydrogen bonding) has roughly nine times the vapor pressure of ethanol at 25°C (about 71.7 kPa versus about 7.9 kPa; ethanol bp 78.4°C, with a strong hydrogen-bonding network), resulting in significantly faster evaporation under identical conditions — a direct macroscopic manifestation of molecular-scale interactions.
Further Knowledge: This principle underpins solvent selection in labs (e.g., ether for rapid extraction drying, ethanol for controlled reactions); also explains everyday phenomena (e.g., hand sanitizer (alcohol-based) cools the skin faster than a glycerin-based lotion).

Prompt Grounding rubric:
level_1: No glass plate is shown; no liquid patches appear; or liquid appears on some other surface (metal, plastic, skin); there's no left/right labeling or it's reversed; nothing distinguishes the two liquids from each other; the air around them clearly isn't still (e.g., a visible fan, smoke, or fluttering object).
level_2: A glass plate is shown but it's dirty, scratched, or hazy rather than clean and clear; the two liquid patches are visibly unequal in size or shape; left/right placement is unclear (no spatial labeling, inconsistent orientation, or labels blocked); one of the two patches is simply missing; something in the background clearly moves due to air currents (fluttering paper, drifting dust), contradicting still air.
level_3: A clean glass plate is shown with two liquid patches of roughly equal size (no more than about a 20% difference in area) placed side by side on it, each spreading into a thin, shallow pool rather than beading up, consistent with how these low-surface-tension liquids wet clean glass; the left patch is labeled or otherwise identifiable as ethanol, the right as ether; the air looks still, but the labeling is partly hard to read or doesn't clearly follow the left-ethanol/right-ether arrangement.
level_4: A clean, flat, clear glass plate under even lighting holds two thin, flat, spread-out liquid pools of nearly the same initial size (within about 10% of each other), separated by a clear gap of at least roughly 5 mm; legible waterproof labels sit outside the plate's edge: 'Ethanol' on the left, 'Ether' on the right; nothing in the background suggests moving air (no motion blur, no drifting particles).
level_5: Everything matches precisely: (i) the glass plate is spotless and glare-free; (ii) the two liquid patches start at essentially the same volume and both spread into thin, low-profile pools with a shallow contact angle typical of a wetting liquid on clean glass, rather than beaded droplets; (iii) the ethanol patch is unambiguously on the left and the ether patch on the right; (iv) the labels are clear, non-overlapping, and placed outside the plate; (v) the surroundings show no motion at all (no drifting particles, no surface changes, nothing suggesting airflow), fully matching 'exposed to still air.'

Scientific and Causal Correctness rubric:
level_1: No evaporation is visible: both patches stay the same size the whole time; or the ether patch actually grows; or the ethanol patch disappears before the ether one; or either patch bubbles, boils, or changes color, none of which is physically right for room-temperature evaporation.
level_2: Evaporation happens, but the relative speed is wrong: the ethanol patch disappears before the ether one, or they vanish at the same time; or one of the patches does something odd (breaking apart suddenly, crawling across the plate, forming a skin); there's no clear sense that one liquid is evaporating faster than the other because of what it is.
level_3: The ether patch visibly shrinks faster than the ethanol patch; the shrinking is steady and continuous, without pausing or growing back; the ether patch fully disappears a clearly noticeable interval before the ethanol one does, but there's no way to judge the exact timing (no clock or clear time reference), and the shrinking looks a bit uneven or jerky rather than smooth.
level_4: The ether patch shrinks noticeably faster than the ethanol patch throughout, its diameter decreasing at roughly 2.5 times the rate of the ethanol patch, visible just from comparing the two side by side; its edge recedes evenly and stays clean (no sticking in odd spots or ragged tearing); the ethanol patch shrinks slowly and is still clearly present well after the ether patch is gone; the difference in speed is plain even without any labels, though nothing on screen explains it in words.
level_5: The comparison is fully convincing: (i) the ether patch disappears completely within roughly 6-8 seconds at room conditions, while the ethanol patch still retains at least roughly 30% of its original area at that point; (ii) each patch's area shrinks at a fairly steady rate over time (consistent with ordinary diffusion-limited evaporation) rather than slowing down and lingering forever, so the ether patch reaches zero at a clear, observable moment rather than just fading asymptotically; (iii) nothing (glare, distortion, halo) gets in the way of comparing the two sizes; (iv) the difference in speed is exactly what you'd expect from ether's much weaker intermolecular attraction (no hydrogen bonding) compared to ethanol's strong hydrogen bonding, shown purely through how the two patches behave, with no on-screen text explaining it.

Spatiotemporal Consistency rubric:
level_1: The two patches don't sit on the same visible plane (e.g., one looks like it's floating above the plate); the video has obvious jump cuts or freezes; the lighting is uneven in a way that makes one side look lit and the other dark; a hand enters and leaves the frame inconsistently, appearing or disappearing without a clear reason.
level_2: Both patches sit on the plate, but they're misaligned vertically (one appears higher or lower than the other); glare unevenly obscures one patch more than the other; the video's pacing changes unevenly (e.g., the ether patch's evaporation looks sped up partway through while the ethanol one doesn't); a hand is visible near only one of the two patches, breaking the symmetry of the setup.
level_3: Both patches sit on the same flat surface with parallel edges; the lighting is even but slightly directional, causing a mild uneven highlight; the video plays at a steady pace overall but has a brief stutter partway through; any hand used to place the liquids is fully out of frame before evaporation is shown.
level_4: The two patches sit flush on the same surface, evenly lit with no harsh shadows so both are equally easy to see; the video plays at a steady, even pace with no speed-ups or slow-downs; the camera doesn't pan, zoom, or shift; everything on screen changes gradually: nothing teleports, flickers, or visibly glitches.
level_5: Excellent consistency throughout: (i) the plate, the two patches, and their labels all keep the same relative position across the whole video; (ii) the lighting stays the same brightness and color the whole time, with no shift; (iii) the ether patch's edge recedes at a smooth, visually steady rate that a viewer could track by eye, and the ethanol patch does the same at its own, slower, equally smooth rate; (iv) there's no visible distortion, no lens warping, and no motion blur that looks physically wrong. Every frame looks like it could be a real, continuous recording.