Domain: Natural Science — Chemistry
Target concept: Preparation of oxygen by heating potassium chlorate

Video generation prompt: A test tube holds a white mixture of potassium chlorate and manganese dioxide. It is fitted with a one-holed stopper and a delivery tube that leads into an inverted, water-filled glass cylinder standing in a water trough, and a glowing splint waits nearby. The bottom of the test tube is being heated by an alcohol lamp.

Evaluation guide:
Target Concept: Catalytic thermal decomposition of potassium chlorate (KClO₃) into potassium chloride (KCl) and oxygen gas (O₂), accelerated by manganese dioxide (MnO₂) without consumption. Minimum Mechanistic Assumptions: (1) KClO₃ is thermally unstable above ~400°C but requires catalyst for safe, controllable O₂ evolution at lower temperatures; (2) MnO₂ is physically and chemically inert under these conditions, with no color/phase change; (3) O₂ is colorless, odorless, supports combustion uniquely; (4) gas evolution is endothermic and strictly dependent on sustained localized heating. Phased Storyline: [Phase 0: Baseline] Static shot: white powder in clear tube, blue flame idle nearby. [Phase 1: Initiation] Flame contacts tube bottom → 10–15 s latency → first bubble emerges *only from delivery tube tip*. [Phase 2: Production] Steady stream of uniform bubbles displaces water in inverted cylinder. [Phase 3: Verification] Cylinder removed → glowing splint inserted → *instant, bright flame reignition*. [Phase 4: Confirmation] Tube cooled → residue inspected → identical white/gray powder, dry and granular. Visibility Constraints: Camera must frame tube bottom *and* delivery tip simultaneously; splint test must show close-up of ember contact with gas; residue comparison requires side-by-side or split-frame pre/post focus. Perspective must be frontal, eye-level, unobstructed, with no hands in frame except during splint insertion.

Manual:
I. Basic Demonstration Information
Demonstration Title: Preparation of Oxygen by Heating Potassium Chlorate (with Manganese Dioxide Catalyst)
Subject: Natural Science - Chemistry - Gas Preparation
Demonstration Purpose: To visually demonstrate the thermal decomposition of potassium chlorate catalyzed by manganese dioxide, producing oxygen gas; to observe the characteristic phenomenon of continuous, steady gas evolution (bubbling in water) and confirm oxygen via glowing splint reignition; to establish visual recognition of catalyst role (unchanged appearance post-reaction) and distinguish reactant mixture state (white crystalline powder) from reaction onset (gas evolution at heated zone).

II. Demonstration Carrier/Equipment
Core Carrier: Dry test tube (15×125 mm, clear borosilicate glass) containing a homogeneous white mixture of potassium chlorate (KClO₃) and manganese dioxide (MnO₂) in ~3:1 mass ratio (visually indistinguishable as uniform white powder); alcohol lamp with blue flame (visible cone and tip); delivery tube (glass + rubber tubing); inverted graduated cylinder or gas jar filled with water and submerged in water trough; glowing splint (wooden, 3–4 cm, recently extinguished but still ember-red at tip).
Auxiliary Equipment: Test tube holder (metal, insulated grip); heat-resistant mat; safety goggles (worn by demonstrator); fume hood or well-ventilated area.

III. Demonstration Content Description
Layout: Test tube held vertically (or slightly tilted downward at mouth) in test tube holder; bottom third of test tube positioned directly in the outer blue cone of the alcohol lamp flame. Delivery tube inserted through one-holed stopper, sealed tightly into test tube mouth, leading to inverted water-filled cylinder in trough.
State Control: Mixture must appear dry, free-flowing, and uniformly white *before heating*. No visible moisture, clumping, or discoloration. Heating applied *only to the bottom* — no flame contact with stopper or upper tube wall. Gas collection begins only *after* sustained heating (≈10–15 s), confirming thermal initiation.
Comparison Baseline: Pre-heating frame shows static white powder; post-heating frame shows dynamic gas evolution *originating exclusively from the heated zone* and traveling upward through delivery tube — establishing causal link between localized heating and gas production.

IV. Observation of Core Phenomena
Pre-Heating Visual Baseline: Test tube contains a smooth, dry, uniformly white granular/crystalline mixture — no gloss, no yellow/brown tint, no visible black specks (MnO₂ is finely dispersed and appears white *in mixture* due to dominance of KClO₃). Alcohol lamp flame is steady, conical, predominantly blue with faint violet tip.
Onset of Reaction: After ≈10–15 s of sustained bottom heating, *first visible bubbles* emerge *from the delivery tube tip* into the inverted cylinder — not from tube interior or stopper. Bubbles are colorless, spherical, rise steadily, and increase in frequency — confirming gaseous product formation.
Gas Collection Phase: Continuous stream of uniform, colorless bubbles fills the cylinder from bottom up, displacing water — demonstrating volumetric gas evolution. No smoke, fumes, spattering, or color change in solid residue.
Oxygen Verification: Once cylinder is ~⅔ full, it is carefully removed and a glowing splint is inserted into the mouth of the cylinder. Splint *immediately reignites with a bright, sustained flame* — definitive visual signature of oxygen.
Post-Reaction Residue Check: After cooling, test tube contents remain a dry, *unchanged white-to-light-gray powder* — no melting, charring, or darkening; MnO₂ catalyst retains physical integrity and color neutrality in mixture, confirming its non-consumption.
Characteristic Stability & Causal Link: Gas evolution ceases immediately upon flame removal; resumes only upon reapplication — proving heating is the essential energy input. All phenomena occur *sequentially and irreversibly*: heating → localized solid stability → bubble onset → steady stream → water displacement → reignition.

V. Summary of Key Knowledge Points and Principles
Core Chemical Principle: 2KClO₃(s) →[MnO₂, Δ]→ 2KCl(s) + 3O₂(g). MnO₂ acts as a heterogeneous catalyst — lowers activation energy, remains chemically unchanged, and is recoverable.
Visual Feature Recognition Logic:
- White powder + blue flame + *delayed onset* of bubbling → confirms endothermic decomposition requiring activation energy.
- Bubbles *only from delivery tube*, *not from solid surface* → confirms gas is evolved *from reaction*, not air expansion.
- Glowing splint reignition → unambiguous functional identification of O₂ (not CO₂, H₂, etc.).
- Residue remains white/gray, dry, powdery → confirms catalyst inertness and absence of side reactions (e.g., no brown Mn₂O₃ formation, no yellow KClO₄).
Safety-Critical Visual Cues: No popping, spitting, or rapid pressure buildup — validates controlled, catalyzed pathway vs. explosive uncatalyzed decomposition.

VI. Demonstration Precautions
- Must use *pure, dry* KClO₃ — contaminated or damp samples may decompose prematurely or violently.
- MnO₂ must be finely powdered and evenly mixed — lumps cause uneven heating and inconsistent bubbling.
- Flame must *never touch rubber tubing* — risk of melting and gas leak.
- Splint test must be performed *immediately after collection* — O₂ diffuses rapidly; delay causes false negative.
- Demonstration duration limited to ≤90 s total; video capture spans roughly 20 s and shows the full causal sequence in order: a brief baseline, 10–15 s of visible heating before the first bubble appears, steady bubbling and water displacement, cylinder removal with the splint test, and the final residue check.

Prompt Grounding rubric:
level_1: No test tube is present; or the tube holds a liquid, a colored solid (e.g., purple potassium permanganate), or a black powder alone rather than a white mixture; no alcohol lamp is present, or its flame is yellow/orange and flickering rather than the typical blue alcohol flame; no heating action is directed at the tube; no delivery tube, stopper, water-filled collection cylinder, or glowing splint appears anywhere in the scene; or the scene shows unrelated apparatus (e.g., a plain beaker, a Bunsen burner and hose, an unrelated plant setup).
level_2: A test tube with some white material is present, but the mixture looks wet, clumped, yellowish, or has obvious black grains standing out against the white; the alcohol lamp's flame is aimed at the middle or top of the tube rather than the bottom, or looks unnaturally colored (e.g., green); a delivery tube is visible but is disconnected from the stopper or hangs loose in the air rather than reaching into water; the collection cylinder is missing its water trough or stands upright out of the water; no glowing splint appears anywhere in the scene; the tube, lamp, delivery tube, and cylinder look jumbled together rather than arranged as a working setup.
level_3: The test tube holds a visibly white, dry, granular mixture; the alcohol lamp's blue flame sits near the tube but does not clearly touch the lower third of the glass; the delivery tube is attached to the stopper but its open end sits above the waterline rather than submerged; the collection cylinder is inverted but only partly below the water's surface; a glowing splint is visible somewhere in the scene, though not yet positioned near the cylinder mouth.
level_4: The test tube holds a uniform white powder; the alcohol lamp's blue flame is stably positioned against the lower third of the tube; the delivery tube runs securely from the stopper into the inverted, water-submerged cylinder; a glowing splint sits ready nearby; all core objects (tube, lamp, delivery tube, cylinder, splint) are present, correctly shaped, and proportioned to one another; only a minor flaw remains, such as the flame being slightly oversized or the splint positioned a bit far from the cylinder mouth.
level_5: The scene matches the prompt precisely: the test tube holds a homogeneous, dry, matte-white powder with no visible gloss or dark specks; a sharp, stable blue conical alcohol-lamp flame touches the lower third of the tube's exterior; a tightly fitted one-holed stopper carries a delivery tube that descends cleanly into an inverted, fully water-submerged glass cylinder resting in a trough; a glowing splint waits within reach of the demonstrator's hand, its tip visibly smoldering, ready for use; every object is correctly shaped, sized, and positioned relative to the others exactly as described.

Scientific and Causal Correctness rubric:
level_1: No gas bubbles ever appear despite sustained heating; a glowing splint inserted into the collected gas goes out or merely smolders rather than flaring; the solid visibly melts, chars, or turns brown/black while heating; bubbles appear before the flame ever touches the tube, breaking the causal link between heating and gas release; violent spattering, smoke, or a loud pop accompanies the heating.
level_2: Bubbles appear, but sporadically or sluggishly, or they originate from the tube wall or around the stopper rather than from the delivery tube's tip; a glowing splint brightens somewhat when inserted but never bursts into flame; the leftover solid turns visibly gray or yellowish rather than staying white, suggesting an unexplained change in the catalyst; bubbling stops abruptly while the flame is still applied, with no clear cause.
level_3: Steady bubbles emerge from the delivery tube's tip only after the flame has been applied for a while, but the delay before the first bubble looks short (well under 10 seconds) rather than the extended latency expected for this catalyzed reaction; a glowing splint reignites but weakly, with a small flame lasting under a second; the leftover solid looks a little darker than the starting powder but is still clearly powdery; bubbling continues briefly for a moment after the flame is pulled away.
level_4: The first bubble appears only after a clear delay of at least 10 seconds of continuous heating, consistent with the catalyzed reaction needing time to reach temperature; bubbles are then uniform, spherical, and continuous, coming only from the delivery tip; a glowing splint reignites vigorously with a sustained flame lasting more than 2 seconds; the leftover solid stays dry, free-flowing, and visually unchanged in color; bubbling stops within a couple of seconds of removing the flame; only a small mismatch remains, such as the splint being inserted a bit late or the residue not looking fully cooled.
level_5: The full causal chain plays out clearly and in order: heating begins, roughly 10–15 seconds pass with no visible gas before the first bubble appears exactly at the delivery tube's tip, the bubble stream then steadily intensifies, the glowing splint is inserted while gas is actively collecting and flares up brightly and immediately, bubbling stops within a second or two of the flame being withdrawn, and the cooled leftover powder looks identical in color, texture, and flowability to the powder before heating. The entire sequence visually confirms that manganese dioxide is catalyzing, not participating in, the decomposition of potassium chlorate into potassium chloride and oxygen.

Spatiotemporal Consistency rubric:
level_1: The test tube appears to float with no visible clamp or stand; the flame looks detached from the tube's surface; the delivery tube bends at an impossible angle as if floating in space; the collection cylinder hovers above the water instead of resting in it; the splint moves into frame with no hand visible; the video jumps straight from 'flame lit' to 'cylinder full' to 'splint glowing' with no visible progression in between.
level_2: The tube tilts down at a steep, unnatural angle; the flame sits noticeably off to the side of the tube rather than beneath it; the delivery tube looks kinked though gas still seems to pass through it; the water level around the cylinder changes inconsistently between shots; the hand holding the splint is posed unnaturally (e.g., an oddly bent wrist); the heating and the first bubble seem to skip past several seconds with no smooth transition, and the bubbling rate changes suddenly rather than gradually.
level_3: The tube stays close to vertical with only a slight tilt; the flame stays roughly centered under the tube's lower third; the delivery tube runs straight and smoothly down into the water; the cylinder stays fully inverted and submerged; the splint is held securely between the fingers; the flow of time from heating to bubbling reads smoothly overall but with a brief hitch, or the leftover residue is shown before the splint test instead of after, breaking the expected order of events.
level_4: The tube, lamp, delivery tube, and cylinder all keep consistent scale, lighting, and camera perspective throughout; the flame stays stable with a soft blue gradient; the water surface stays calm with a gentle meniscus; bubbles rise at a natural, unhurried pace; the splint approaches the cylinder mouth in one smooth motion; the whole sequence flows without visible skips or repeats; only a minor issue remains, such as a small shift in camera angle between the heating shot and the splint-test shot, or ripples in the water that look a bit too strong.
level_5: The entire clip holds together as one physically consistent scene from start to finish: the tube stays rigidly held with no wobble, the lamp and flame stay steady without swaying, lighting stays even with no stray glare on the glass and the water's refraction looks natural; bubbles grow slightly larger as they rise and ascend at a steady, believable rate; the demonstrator's hand enters frame holding the splint only after the cylinder has been lifted out of the trough, moving with a natural wrist motion; the whole sequence (from the flame first touching the tube, through steady bubbling, to the splint flaring at the cylinder mouth and the final view of the residue) plays out smoothly with no visible stutters, freezes, or skips.