Domain: Natural Science — Chemistry
Target concept: Mixing silver nitrate solution with sodium chloride solution produces a white silver chloride precipitate.

Video generation prompt: Add the clarified silver nitrate aqueous solution to a beaker containing the clarified sodium chloride aqueous solution, and gently swirl to mix.

Evaluation guide:
Target concept: Precipitation reaction defined by instantaneous, stoichiometric formation of an insoluble ionic solid (AgCl) from mixing two soluble electrolytes (AgNO₃ and NaCl) in aqueous phase. Minimum mechanistic assumptions: (i) Ag⁺ and Cl⁻ ions exist freely and are mobile in solution; (ii) AgCl has negligible solubility (Ksp = 1.8×10⁻¹⁰), so ion collision leads directly to nucleation; (iii) visual detectability requires sufficient particle density (>10⁹ particles/mL) to scatter visible light uniformly. Phased storyline: (1) Baseline: static, colorless, transparent NaCl solution in beaker on white background; (2) Causal trigger: vertical addition of colorless AgNO₃ solution: no splash, no wall contact; (3) Nucleation onset: sub-second localized cloudiness at interface; (4) Dispersion & homogenization: gentle swirl enables rapid ion mixing and uniform particle suspension; (5) Stable endpoint: fully opaque, matte, pure white turbidity filling entire solution volume, persistent for ≥5 s with no settling or color shift. Visibility constraints: must be filmed frontally under neutral white light; white background mandatory; resolution sufficient to distinguish matte white suspension from clear liquid or false positives (bubbles, dust); no occlusion of beaker interior; perspective must show full depth of liquid column to verify uniformity.

Manual:
I. Basic Demonstration Information
Demonstration Title: Silver Nitrate and Sodium Chloride Reaction Producing White Silver Chloride Precipitate Demonstration
Subject: Natural Science - Chemistry - Chemical Reactions and Precipitation
Demonstration Purpose: To visually demonstrate the formation of a white precipitate (AgCl) upon mixing clarified aqueous solutions of silver nitrate and sodium chloride; to establish visual recognition of precipitation as evidence of a double displacement reaction; and to train accurate observation of color, state (clear → cloudy/white suspension), and spatial distribution (uniform fine white particles suspended in liquid) as diagnostic features of chemical change.

II. Demonstration Carrier/Equipment
Core Carrier: Clarified 0.1 M silver nitrate (AgNO₃) aqueous solution (colorless, transparent); clarified 0.1 M sodium chloride (NaCl) aqueous solution (colorless, transparent); clean 100 mL beaker (transparent borosilicate glass, marked with volume graduations, no scratches or stains).
Auxiliary Equipment: Dropper or graduated pipette (with clear calibration, tip intact); white ceramic tile or light-colored lab bench background (to enhance contrast for white precipitate detection); stopwatch (for timing demonstration duration); safety goggles and lab coat (worn by demonstrator).

III. Demonstration Content Description
Layout: Place the clean, dry 100 mL beaker on the white background. Pre-fill it with exactly 50 mL of clarified NaCl solution (visually confirmed colorless and particle-free). Position the AgNO₃ solution in a labeled reagent bottle beside the beaker. Ensure lighting is bright, diffuse, and frontal (no glare or shadows obscuring beaker contents).
State Control: Both solutions must be at room temperature (20–25°C), clarified (no turbidity or sediment), and freshly prepared or filtered if stored. No bubbles, dust, or condensation on beaker walls before addition.
Addition Protocol: Using the dropper/pipette, carefully add 5 mL of AgNO₃ solution vertically into the center of the NaCl solution in the beaker — no splashing, no contact with beaker walls. Immediately after addition, gently swirl the beaker clockwise 3–4 times (≈2 seconds total), maintaining steady hand motion and minimal tilt (<15°), to ensure homogeneous mixing without agitation-induced foaming or splatter.

IV. Observation of Core Phenomena
Initial State (Pre-mixing): Beaker contains only colorless, transparent NaCl solution — no haze, no particles, no coloration. Liquid surface is still and reflective.
Transition Event (0–1 s post-addition): Instantaneous contact between AgNO₃ and NaCl solutions triggers immediate localized cloudiness at the point of entry (visible as faint milky streaks descending), followed by rapid dispersion.
Final State (Within 3 s post-swirl): Entire solution becomes uniformly turbid/milky-white due to formation of fine, suspended AgCl particles. No settling observed during observation window (≥5 s). The suspension is opaque white (not gray, yellow, or blue), with matte, non-glossy appearance — distinct from undissolved solids or oil droplets. Under direct lighting, the white precipitate exhibits soft scattering (no sharp reflections), confirming colloidal/suspended solid nature.
Visual Feature Recognition Comparison: Contrast against control expectation — if no reaction occurred, solution would remain colorless and transparent; the emergence of uniform, opaque white turbidity — not yellow (AgBr), not pale yellow (AgI), not brown (Ag₂O) — is the definitive visual signature of AgCl formation.

V. Summary of Key Knowledge Points and Principles
Core Concept Definition: A precipitation reaction is a type of double displacement (metathesis) reaction in which two soluble ionic compounds exchange ions to form an insoluble product (precipitate) and a soluble salt. Here: AgNO₃(aq) + NaCl(aq) → AgCl(s)↓ + NaNO₃(aq).
Principle of Visual Feature Recognition: AgCl is uniquely characterized by its *instantaneous formation*, *pure white color*, *fine particulate suspension* (not granular or flaky), and *opacity without sedimentation within short observation time*. Its whiteness is distinguishable from other silver halides (e.g., AgBr: pale yellow; AgI: yellow) and from physical contaminants (e.g., dust: irregular shape, inconsistent dispersion; starch: bluish tint under iodine test — irrelevant here). The visual transition from “clear → uniformly white turbid” is the causal perceptual anchor linking reagent mixing to chemical change.

VI. Demonstration Precautions
Solution Clarity: Filter both solutions through 0.45 μm membrane filters if any doubt about clarity; discard if cloudy or discolored.
Lighting & Background: Use neutral white LED lighting (5000K) and white background — avoids chromatic distortion (e.g., yellow light making AgCl appear cream) and maximizes contrast for white-on-white detection.
Swirling Technique: Swirl must be gentle and brief — vigorous stirring may cause air entrainment (bubbles mimicking turbidity) or wall adhesion masking uniformity.
Timing: Observation window begins at first drop contact and ends at 5 s post-swirl; precipitate must be fully developed and uniformly distributed by then.
Safety: AgNO₃ stains skin and surfaces black; wear gloves if handling open bottles; avoid skin contact. All waste collected in designated halide waste container.

Prompt Grounding rubric:
level_1: No beaker is shown, or no liquid is visible in it; the addition of AgNO₃ is never shown, or it's poured into the wrong container (e.g., a test tube or flask instead of the beaker); there's no swirling motion at all; either liquid is visibly colored (e.g., yellow or blue) or cloudy before mixing; or the background is dark or patterned rather than plain, making it hard to see anything against it.
level_2: A beaker with liquid is shown, but it's unclear whether the liquid is colorless before mixing; the AgNO₃ solution is poured straight from a bottle rather than added with a dropper or pipette; there's no swirling, or the beaker is shaken or stirred vigorously instead of gently swirled; the background is a non-plain surface (e.g., wood grain or a gray countertop) rather than light and plain; a core item like the dropper or a labeled reagent is missing.
level_3: The beaker holds a visible volume of liquid roughly matching 50 mL; AgNO₃ is added with a dropper or pipette aimed at the center of the liquid; a gentle swirl of about 3–4 rotations follows; the background is light-colored but not a clean white (e.g., an off-white tile); both liquids look colorless before mixing, though minor issues like glare or slight blur reduce clarity; all core items are present but details like labels or volume markings are missing.
level_4: The beaker holds about 50 mL of visibly colorless NaCl solution; AgNO₃ is added via a dropper aimed at the center of the liquid; a gentle swirl of about 3–4 smooth rotations follows, with minimal tilt (well under 15°); the background is plain and light; both liquids are unambiguously colorless before mixing; there's no splashing, no bubbles, and no contact between the dropper and the beaker wall; only very minor flaws remain, such as the dropper being slightly out of focus or a faint shadow on the beaker base.
level_5: The beaker is clean and shows a clear ~50 mL fill of NaCl solution with a visible, undisturbed liquid surface; the AgNO₃ solution in its bottle looks equally clear and colorless; the dropper delivers roughly 5 mL with a precise vertical entry straight into the center of the liquid, with no contact with the beaker wall and no splashing; the swirl that follows is smooth and controlled, exactly 3–4 steady rotations with minimal tilt; the background is a uniform, high-contrast plain surface; lighting is even and frontal with no glare, and all equipment is used the way it would be in a real lab.

Scientific and Causal Correctness rubric:
level_1: The solution stays perfectly clear the whole time, or a precipitate does form but in the wrong color (e.g., yellow, brown, or gray) or the wrong texture (e.g., large flakes or an oily film); or cloudiness is already present before the AgNO₃ is even added; or there's no clear link between adding/swirling the solution and the cloudiness appearing.
level_2: Cloudiness appears, but only after a long delay (more than 3 seconds) following the swirl, or only in patches rather than spreading through the whole beaker; the precipitate looks glossy or metallic rather than matte; the color leans off-white, creamy, or bluish rather than plain white; or the sequence of events (adding, then swirling, then cloudiness) is out of order.
level_3: White cloudiness fills more than 80% of the solution within 2–3 seconds of swirling, though small non-uniformities remain: a faint clear ring near the surface, or a slight gradient from top to bottom; the cloudiness looks white but a bit too translucent rather than fully opaque; the order of events (add → swirl → cloudiness) is correct, but the timing feels loose or delayed.
level_4: Even, opaque white cloudiness fills the whole beaker within about 2 seconds of swirling; the precipitate has a soft, matte look with no shine or graininess; the color stays a clean white with no tint; the cloudiness clearly builds up gradually and only after the swirling, with no stray bubbles, dust specks, or other artifacts confusing the picture.
level_5: Cloudiness starts right at the point where the AgNO₃ meets the NaCl solution, spreads outward, and becomes fully even and opaque shortly after swirling ends; the final result is a uniform, fully white, fully opaque suspension with no settling, no clear patches, and no shine, matching what an AgCl precipitate should look like; the whole sequence (clear liquid → localized cloudiness → uniform turbidity) happens in a clear, physically sensible order with no delays or reversals.

Spatiotemporal Consistency rubric:
level_1: Basic physical continuity breaks down: the liquid looks solid rather than fluid, the beaker changes shape during the swirl, the dropper appears to pass straight through the beaker wall, precipitate particles drift upward instead of settling or dispersing normally, or the turbidity is present and then gone before the swirling even happens; frames jump forward and skip the key moments of mixing, or clear and fully turbid frames are intercut with no transition between them.
level_2: The swirl looks jerky or unnaturally fast rather than a smooth hand motion; the falling droplet curves upward instead of dropping straight down; cloudiness appears in the liquid before the addition has finished; the beaker's outline warps oddly (e.g., looks oval instead of round) at some point; the lighting shifts abruptly mid-sequence with no apparent cause (e.g., a sudden jump from bright to dim); there's an unexplained pause of more than a second between adding the solution, swirling, and the turbidity appearing.
level_3: Minor issues remain: motion blur during the swirl makes it hard to count the rotations; the falling droplet looks a different size than what the dropper would produce; the precipitate looks slightly denser near the bottom of the beaker without any real settling; the lighting tone shifts slightly warmer or cooler partway through; the background shifts slightly between shots; the overall pace speeds up briefly during a non-critical moment.
level_4: Motion looks physically believable throughout: the droplet falls straight down and speeds up naturally under gravity, the swirl rotates smoothly at a steady rate, and the cloudiness spreads outward from the point of entry in a natural, radiating way; lighting and camera angle stay fixed with no warping of the beaker's shape; the sequence (clear liquid, first cloudiness, full turbidity) unfolds smoothly and in the right order at a believable pace (the addition takes about half a second, swirling lasts a couple of seconds, and the liquid turns fully cloudy shortly after swirling stops).
level_5: The whole clip holds together with no visible flaws: camera position, focus, and lighting direction/intensity stay constant throughout; the droplet's impact causes a small, natural ripple or dimple on the liquid surface; the swirl creates a visibly coherent rotating flow rather than random turbulence; the white precipitate nucleates and spreads smoothly and continuously with no sudden jumps, freezes, or speed changes; the pacing feels like real time throughout, with the turbidity fully developing shortly after the swirl ends rather than at an arbitrary or inconsistent moment.