Domain: Natural Science — Chemistry
Target concept: Carboxylic acid reacts with sodium bicarbonate to produce bubbles.

Video generation prompt: Add 1 mL of 0.1 M acetic acid solution to 2 mL of saturated NaHCO₃ solution and observe for several seconds.

Evaluation guide:
Target concept: Carboxylic acid functionality is operationally defined by its ability to protonate bicarbonate ion (HCO₃⁻), yielding CO₂ gas, a rapid, stoichiometric, and visually unambiguous reaction. Minimum mechanistic assumptions: (i) acetic acid is a Brønsted acid (CH₃COOH ⇌ CH₃COO⁻ + H⁺); (ii) H⁺ reacts with HCO₃⁻ to form H₂CO₃, which spontaneously decomposes to CO₂(g) + H₂O; (iii) CO₂ gas manifests macroscopically as discrete, buoyant, spherical bubbles in aqueous solution. Phased storyline: (1) Pre-addition baseline: motionless, clear, reflective liquid surface (2 s); (2) Causal trigger: acid contacts NaHCO₃ solution, instantaneous (≤0.8 s) nucleation of bubbles at interface; (3) Effect propagation: bubbles rise uniformly through column, forming transient froth (3–12 s); (4) Steady-state verification: continuous, non-decaying effervescence with stable bubble morphology and liquid clarity (≥10 s total observable). Visibility constraints: camera must capture mid-column bubble ascent against high-contrast white background; no obstructions; focus sharp enough that individual bubbles are distinguishable rather than a blurred froth; lighting must reveal translucency (not just outlines).

Manual:
I. Basic Demonstration Information
Demonstration Title: Carboxylic Acid Reacts with Sodium Bicarbonate to Produce Bubbles (Acetic Acid + NaHCO₃ Effervescence) Demonstration
Subject: Natural Science - Chemistry - Acids and Bases / Gas Evolution Reactions
Demonstration Purpose: By adding 1 mL of 0.1 M acetic acid solution to 2 mL of saturated sodium bicarbonate (NaHCO₃) solution, this demonstration visually confirms the characteristic effervescence (bubbling) resulting from CO₂ gas evolution — a hallmark diagnostic test for carboxylic acids; it reinforces the acid–carbonate reaction principle; and it trains visual recognition of gas evolution as a key macroscopic indicator of chemical reactivity.

II. Demonstration Carrier/Equipment
Core Carrier: 0.1 M acetic acid solution (clear, colorless, mild vinegar odor), saturated aqueous NaHCO₃ solution (clear, colorless, no visible precipitate), clean 10 mL graduated cylinder or volumetric pipette (for precise 1 mL and 2 mL measurement), 50 mL transparent glass beaker (wide-mouthed, flat-bottomed, marked with volume graduations), white ceramic tile or light-colored background (to enhance bubble contrast), stopwatch or timer.
Auxiliary Equipment: Lab gloves, safety goggles, fume hood (optional, though low-risk at this scale), dropper or calibrated syringe (for controlled addition).

III. Demonstration Content Description
Layout: Place the beaker on the white background under even ambient lighting (no backlighting or glare). Pre-measure and pour 2 mL of saturated NaHCO₃ solution into the beaker. Confirm its clarity and absence of pre-existing bubbles or cloudiness. Then, using a calibrated dropper/syringe, precisely add 1 mL of 0.1 M acetic acid solution down the inner wall of the beaker (not directly onto surface) to minimize splashing and ensure controlled mixing.
State Control: Maintain room temperature (20–25°C); avoid agitation post-addition except gentle swirling *only if required for observation* — but primary observation must capture *spontaneous, immediate bubbling upon contact*. No heating or external catalysts.
Comparison Baseline: A control setup (2 mL saturated NaHCO₃ alone, no acid added) is *not shown in video* but is implied for scientific reasoning; the core visual baseline is “still, clear solution → sudden onset of vigorous bubbling”.

IV. Observation of Core Phenomena
Initial State (Pre-Addition): NaHCO₃ solution is perfectly clear, colorless, motionless, with no suspended particles or bubbles — surface is mirror-smooth and reflective.
Transition Moment (0–2 s after addition): Immediate (≤1 s), localized bubbling begins at the interface where acetic acid contacts NaHCO₃ — tiny, spherical, translucent bubbles nucleate and rise rapidly. Bubbling intensifies within 2 seconds.
Peak Effervescence (2–15 s): Sustained, vigorous, continuous stream of small-to-medium (0.5–2 mm diameter) CO₂ bubbles rising uniformly through the liquid column; bubbles coalesce slightly near surface, producing gentle froth or foam layer ≤3 mm thick; solution remains transparent (no cloudiness or precipitate); no color change occurs in either reagent or mixture.
Characteristic Stability: Bubbling persists visibly for ≥10 seconds without cessation or decay during observation window; rate gradually declines after ~12 s but remains clearly observable until at least 15 s. No splattering, boiling, or vapor emission — only quiet, steady gas evolution.
Visual Verification Features:
- Bubble morphology: Spherical, discrete, translucent, non-adherent to beaker wall (freely rising);
- Bubble dynamics: Ascending at constant moderate velocity (~1–3 cm/s), uniform size distribution, no bursting-dominated surface chaos;
- Liquid state: Maintains clarity and fluidity — no turbidity, no solid residue, no phase separation;
- Causal linkage: Bubbling initiates *exclusively and instantaneously* upon acid contact — no delay, no pre-bubbling, no bubbling in control condition.

V. Summary of Key Knowledge Points and Principles
Core Concept Definition: Carboxylic acids react with carbonates/bicarbonates via proton transfer to produce CO₂ gas, water, and salt. Reaction: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂↑. Effervescence is a direct, macroscopically visible signature of CO₂ evolution — a definitive functional group test.
Chemical Significance:
- Diagnostic Utility: This reaction distinguishes carboxylic acids from weaker/non-acidic organics (e.g., alcohols, aldehydes) that do not liberate CO₂ from NaHCO₃.
- Stoichiometric Clarity: 1:1 molar ratio drives rapid completion; excess NaHCO₃ ensures full observable response.
- Safety & Simplicity: Mild exothermicity, no hazardous byproducts — ideal for classroom demonstration.
Further Knowledge: Stronger mineral acids (e.g., HCl) produce faster/more violent bubbling; weaker acids (e.g., phenol, pKa ≈ 10) show no observable reaction — the relevant threshold is each acid's pKa relative to carbonic acid's own first pKa (~6.35): acids substantially stronger than carbonic acid (well below pKa ~6.35) can protonate HCO₃⁻ and release CO₂, while acids at or above that pKa generally cannot.

VI. Demonstration Precautions
Reagent Purity: Use freshly prepared saturated NaHCO₃ (no CO₂ loss from standing); confirm acetic acid concentration (0.1 M ≈ pH ~2.9, sufficient for rapid reaction).
Measurement Accuracy: Volumes must be precise — 1 mL acid + 2 mL NaHCO₃ defines stoichiometric excess of bicarbonate, ensuring unambiguous, sustained bubbling.
Timing Discipline: Observation begins *at moment of acid addition*; the video captures only the first 10–15 s of *onset and peak effervescence*, consistent with the shortened observation window in the prompt and the 10-s generation limit.
Visual Fidelity: Lighting must highlight bubble transparency and motion against white background; camera focus fixed on liquid column mid-height to capture rising bubbles; no zooming or cuts during bubbling phase.

Prompt Grounding rubric:
level_1: No liquids or container shown at all; or the container holds only one liquid (acid or bicarbonate solution, not both) with no addition event; or the two portions look wildly mismatched in size (e.g., roughly equal amounts, or far more than a couple of teaspoons total); or either liquid is visibly colored or cloudy; or the acid is shown going in before any bicarbonate solution is present in the container.
level_2: A container with two liquids is shown, but the smaller (acid) portion looks similar in size to the larger (bicarbonate) portion rather than clearly smaller, or the bicarbonate portion looks only slightly larger than a splash; either liquid appears yellow, brown, or cloudy; the moment of addition happens off-screen or is blocked from view; or the liquid is already moving or disturbed before anything is added.
level_3: The bicarbonate portion is visibly roughly twice the acid portion (consistent with a small container of bicarbonate solution receiving a smaller pour of acid); both liquids look clear and colorless; the liquid sits still before the addition; the acid is poured into the container on camera, but the exact moment addition begins is unclear, or the acid is poured from well above the surface causing a visible splash, or the background behind the container is not a plain light color.
level_4: The bicarbonate-to-acid ratio looks right (roughly 2:1), and if a graduated cylinder or marked container is used, the fill lines sit close to the intended marks; both liquids are clearly clear and colorless; the liquid surface is visibly calm and undisturbed for a second or more beforehand; the acid is poured smoothly down the inside wall of the container rather than dropped from height; the background is plain and light-colored; only one small flaw remains, such as a brief blur during the pour or a slightly off-center frame.
level_5: Every setup detail matches: the bicarbonate portion is clearly about double the acid portion, with any visible graduation marks lining up closely with the 1 mL and 2 mL lines; both liquids are unmistakably clear, colorless, and free of particles; the surface sits perfectly still and reflective for a second or more right before the addition; the acid runs down the inner wall smoothly with no splash or dripping; the background stays plain, light-colored, and fully in frame; the camera stays steady and in focus on the container throughout.

Scientific and Causal Correctness rubric:
level_1: No bubbling occurs at any point, or the liquid stays completely still throughout; or bubbling starts clearly before the acid is added, or only after a long pause (several seconds) once it is added; or the bubbles are large, foamy, and chaotic in a way that looks more like boiling or shaking than a chemical reaction; or the liquid turns cloudy, changes color, or leaves a visible residue.
level_2: Some bubbling occurs, but it stays only at the surface rather than rising up through the liquid, or the bubbles look flattened or stuck against the container wall instead of floating free, or they burst violently with visible splattering; or bubbling only begins after a clear pause (more than a couple of seconds) following the addition; or the liquid turns hazy or cloudy within the first few seconds.
level_3: Bubbling begins soon after the acid touches the bicarbonate solution (within a couple of seconds) and the bubbles rise up through the liquid rather than staying at the surface, but sizes vary noticeably from tiny to large within the same shot, or the bubbling is patchy and on-and-off rather than continuous, or it stays clustered right at the point of contact instead of spreading through the container; the liquid stays clear overall, at most with a very brief passing haze.
level_4: Bubbling begins essentially as soon as the acid contacts the bicarbonate solution; the bubbles are fairly small and similar in size to one another, and they rise continuously through the liquid rather than clumping in one spot; the liquid stays completely clear and colorless the whole time; only a minor flaw remains, such as slightly heavier bubbling on one side of the container.
level_5: Bubbling begins essentially the instant the acid reaches the bicarbonate solution and continues steadily and vigorously without dying down for the whole clip; the bubbles are small and fairly uniform, rising continuously and spreading across the container rather than clumping together or staying only at the contact point; the liquid never clouds, changes color, or leaves any residue; no bubbling appears anywhere in the container before the acid arrives.

Spatiotemporal Consistency rubric:
level_1: The container changes size, shape, or position between shots; bubbles are seen drifting downward or sideways instead of rising; the liquid surface ripples or splashes with nothing visible causing it; a hand or dropper appears or disappears abruptly mid-motion; or the clip visibly freezes or repeats the same moment.
level_2: The dropper or hand vanishes before it actually touches or releases the acid; bubbles rise, then stop, then start again for no visible reason; the background shifts position partway through the clip; or the lighting flickers enough that the bubbles become hard to see for part of the clip.
level_3: Only minor flaws are present: a brief moment, well under a second, where the hand blocks the view of the addition; the background edge is slightly cropped for a couple of frames; or one small bright or dark patch on the container slightly washes out the bubbles' contrast; otherwise the container, hand, and background stay put.
level_4: The hand's motion bringing in and withdrawing the dropper is smooth and physically natural; the bubbles travel in a fairly straight, continuous path upward with no unexplained stalling or reversing; the background stays fully in frame and doesn't shift; the room's brightness stays steady with no sudden flicker or color-temperature shift; only one small imperfection remains, such as a brief soft-focus moment during the bubble rise.
level_5: Nothing in the shot breaks continuity: the container, hand, and background keep the same size, position, and framing for the whole clip; the hand moves through one natural, continuous motion from bringing the acid in to withdrawing it; the bubbles rise smoothly and continuously with none freezing in place, duplicating, or appearing from nowhere; the room's brightness and color stay consistent throughout with no flicker or new light source appearing; and the pacing of the bubbling matches how the reaction would actually unfold in real time, with no visible speeding up or slowing down.