Domain: Natural Science — Chemistry
Target concept: Acetic acid reacts with sodium bicarbonate in a sealed plastic bag and is placed on a balance.

Video generation prompt: A sealed plastic bag containing vinegar and baking soda is placed on a balance; the reactants are mixed inside the bag.

Evaluation guide:
(i) Target concept: An acid–carbonate reaction (acetic acid in vinegar + sodium bicarbonate in baking soda) generates CO₂ gas; because the reaction happens inside a sealed, flexible bag resting on a balance, the CO₂ cannot escape the system, so it accumulates and visibly inflates the bag while the balance's displayed reading stays the same throughout: the bag's volume increases even though its total mass (and therefore the balance reading) does not change, illustrating conservation of mass.
Minimum mechanism: Reaction must occur inside a sealed, flexible, transparent container resting on a balance whose reading display is visible before, during, and after mixing; the two reactants (vinegar and baking soda) must be brought into direct contact without breaking the bag's seal; the CO₂ produced must stay trapped inside the bag (not vented or leaked) so the balance reading is unaffected while the bag's volume grows.
(ii) Storyline: [Frame 0] Sealed bag with separated clear liquid (vinegar) and white solid (baking soda) rests motionless on the balance pan; the balance's reading display already shows a steady value. → [After placement stabilization] A hand squeezes or shakes the bag, bringing the liquid and powder into contact without opening the seal. → [Within the same continuous shot] Bubbles form where the liquid meets the powder and continue rising through the liquid. → [Concurrently] The bag's surface bulges outward and becomes taut as gas collects inside it, while the balance's reading display continues to show the same value it showed before mixing. → [Throughout] A fixed camera keeps the bag and the balance's reading display in view; nothing is added, removed, or repositioned from outside the bag.

Manual:
Experimental Procedure
1. Place a sealed transparent plastic bag containing clear vinegar and white baking soda powder onto the center of a balance pan, and note that the balance's reading display shows a steady value once the bag has settled.
2. While the bag remains on the balance, mix the contents by gently squeezing or shaking the bag so the vinegar and baking soda come into contact, without opening the seal.
Observation of Experimental Phenomena
The sealed bag visibly inflates as carbon dioxide gas is produced; continuous bubbling occurs where the liquid and powder meet; the vinegar stays clear and colorless throughout, with no leakage or gas escaping the bag. Even as the bag's volume grows, the balance's reading display shows the same value throughout the reaction as it did before mixing began.
Summary of Experimental Principles
Acetic acid (in vinegar) reacts with sodium bicarbonate (baking soda) to produce carbon dioxide gas, water, and sodium acetate: CH₃COOH + NaHCO₃ → CO₂↑ + H₂O + CH₃COONa. Because the bag stays sealed, the CO₂ produced cannot escape the system: the total mass of reactants and products on the balance pan is unchanged, so the balance reading stays constant even though the trapped gas causes the bag's volume to visibly increase — a demonstration of conservation of mass.

Prompt Grounding rubric:
level_1: No sealed bag, no balance, and no vinegar (clear liquid) or baking soda (white powder) appear together in frame; none of the required setup elements from the posted_prompt are shown.
level_2: Only some of the required elements appear: for example a bag and a balance are shown but the bag is empty or holds only one reactant, or a balance appears with nothing on its pan, or a bag is shown but not resting on the balance pan, or the bag is not sealed, or the balance's reading display is never visible in the shot.
level_3: A sealed, transparent bag holding a clear liquid (vinegar) and a white powder (baking soda), kept apart from each other, sits on the pan of a balance whose reading display is visible and shows a steady value once the bag has settled; all core objects and the placement action match the posted_prompt, but no mixing action has occurred yet.
level_4: All elements of score 3 are present AND the mixing action is clearly shown (a hand squeezes or shakes the sealed bag so the vinegar and baking soda come into direct contact), with no substitution of materials (no colored liquid standing in for vinegar, no different powder standing in for baking soda) and nothing added to or removed from the bag from outside.
level_5: All elements of score 4 are present AND the sequence and framing are correct throughout: the bag is placed and settles on the pan before the balance's reading display is shown steady, mixing begins only after the bag is stationary, and a fixed camera keeps both the bag and the balance's reading display in view for the whole clip with no other objects entering the shot.

Scientific and Causal Correctness rubric:
level_1: No CO₂ gas production is visible at all (no bubbling, no bag inflation), OR the balance's displayed reading visibly changes as soon as the bag is placed or as mixing begins, wrongly implying the sealed system is gaining or losing mass; the liquid and powder show no sign of reacting.
level_2: The bag inflates or bubbles appear, but the balance's displayed reading visibly rises, falls, or drops to zero at some point while the bag sits on the pan; or the bag's expansion is not clearly tied to the mixing action (it starts long before or long after the reactants touch); or the vinegar turns colored or cloudy, which is not expected for this reaction.
level_3: After mixing begins, bubbles form where the vinegar and baking soda meet and the bag visibly inflates from the trapped gas, while the balance's displayed reading stays the same value it showed before mixing began; the vinegar stays clear and colorless throughout, consistent with CO₂ being produced and trapped rather than escaping the sealed system.
level_4: All elements of score 3 are present AND the relationship is unambiguous: the bag becomes visibly taut and rounded as bubbling continues, the balance's reading is the same single value from before mixing to after the bag is fully inflated, and nothing suggests gas is escaping the bag (no deflation, no visible leak at the seal).
level_5: All elements of score 4 are present AND the demonstration reads as a complete conservation-of-mass argument: bubbling begins promptly once the vinegar and baking soda touch, the bag's expansion continues smoothly as bubbling continues, and the balance's reading is shown steady before mixing, still unchanged partway through the expansion, and still unchanged once the bag stops inflating, with no smoke, flame, fogging, precipitate, or color change appearing anywhere in the clip.

Spatiotemporal Consistency rubric:
level_1: The bag appears already inflated in the very first frame with no earlier flat, just-placed moment shown, or the bag or the balance instantly jumps to a different size or position between one moment and the next, or the balance pan tilts or spins with no visible cause, or the lighting in the shot abruptly swings between bright and dim with no visible cause, or the shot cuts between clearly different camera framings with no transition.
level_2: The bag slides across the pan or lifts off the balance during mixing with no hand visibly moving it, the balance pan appears to bend or flex as if it were rubber, the bag's surface stretches into a shape a thin sealed bag of liquid and gas could not physically hold (sharp corners, folding through itself), or the footage stutters badly enough that the bag's size visibly jumps between adjacent moments instead of growing smoothly.
level_3: The bag stays on the balance pan for the whole clip without sliding, lifting off, tearing, or splitting open; its outline grows continuously as it inflates rather than jumping in size; ordinary room lighting on the bag and pan stays even for the whole clip, with no sudden flash, blackout, or color-tinted wash appearing partway through; brief handheld camera wobble is fine as long as the bag and balance stay recognizable.
level_4: All elements of score 3 are present AND the bag keeps the same position relative to the balance pan throughout: it does not drift toward an edge, rotate, or appear to shrink or grow from a perspective shift independent of its actual inflation; the balance body itself does not shift, tilt, or change apparent size; the bag's surface and the bubbles inside it stay as bright as the rest of the scene as it inflates, with no isolated glow or darkening confined to the bag.
level_5: All elements of score 4 are present AND the bag's outline stays continuous and unbroken from frame to frame as it inflates (no torn edges, no sections disappearing), the balance's pointer or digital readout, if shown, stays legible throughout without flickering, glitching, or freezing into a blank or garbled state, bubbles rise and pop at a steady, plausible pace without strobing on and off, and if a hand enters the frame to squeeze the bag, it is shown withdrawing afterward rather than vanishing mid-shot.