Domain: Healthcare — Clinical Laboratory Science
Target concept: Urinalysis pH Determination

Video generation prompt: A 1 mL volume of fresh urine from a healthy adult was placed in a test tube. Three drops of bromothymol blue reagent were added, the tube was mixed thoroughly, and the change in solution color was observed.

Evaluation guide:
(i) Target concept: Visual confirmation of pH-dependent color transition in urinalysis using bromothymol blue indicator.
Minimum mechanism: Bromothymol blue must exist as a dissolved molecular species in aqueous solution; its protonated (yellow) and deprotonated (blue) forms coexist near its pKa (7.1), yielding green when sample pH falls in the ~6.0–7.6 window; for this demonstration, the urine sample is assumed to fall in that range (a plausible value, since healthy adult urine pH commonly varies from about 4.5 to 8); the urine must be a dilute aqueous matrix with no interfering chromogens or turbidity.
(ii)Storyline: [Phase 1: Baseline] Static frontal view of upright test tube containing pale yellow transparent liquid (~1 mL). [Phase 2: Intervention] Dropper enters frame from top, vertically aligned, releases three discrete spherical droplets that fall freely into tube without splashing or contact with walls. [Phase 3: Transformation] Tube is smoothly rotated/swirled for ≥0.5 s (visually unbroken motion), inducing homogenization. [Phase 4: Outcome] Camera holds fixed on tube for ≥1 s showing uniform green color filling entire liquid column, with no occlusion, no fading, no stratification. All phases occur in same scene, fixed viewpoint, continuous lighting, and unbroken temporal flow.

Manual:
Experimental Procedure
1. Place 1 mL fresh urine in a clear test tube.
2. Add three drops of bromothymol blue reagent using a dropper.
3. Mix tube thoroughly by gentle swirling.
4. Observe final solution color.
Observation of Experimental Phenomena
Urine solution changes from pale yellow to uniform, stable green after mixing.
Summary of Experimental Principles
Bromothymol blue is a pH indicator: yellow below pH 6.0, green between pH 6.0–7.6, blue above pH 7.6. Normal urine pH varies widely (roughly 4.5–8, commonly averaging closer to 6.0); for this demonstration, assume a urine sample at pH ~6.5–7.0, which yields a green color with bromothymol blue.

Prompt Grounding rubric:
level_1: No urine sample visible in a test tube; no bromothymol blue reagent bottle or dropper visible; no addition of reagent into the tube shown; no mixing action shown; no phase showing the tube's color afterward.
level_2: A test tube, a liquid in a tube, or a dropper appears, but the objects are wrong (e.g., a syringe instead of a dropper, a beaker instead of a test tube, or an obviously colored liquid substituting for urine), and none of the four steps (place urine, add drops, mix, observe) occur in order.
level_3: A transparent test tube holds a liquid volume that looks like roughly 1 mL (about a fifth to a third of the tube's height), and a dropper releases three visibly separate droplets into it; a rotating/swirling mixing motion is shown, but the shot cuts away before any dedicated moment of holding on the tube to observe its color afterward.
level_4: All conditions for score 3 are met, and additionally: a distinct post-mix observation beat is shown — the camera holds on the tube for at least a full second after mixing with no cut hiding the transition; the dropper is held upright over the tube while dispensing, and the three droplets fully separate and land inside the tube without merging mid-air or splashing outside it.
level_5: All conditions for score 4 are met, and additionally: exactly three droplets are dispensed, each clearly separated from the others as they leave the dropper; the tube's liquid is a single uncontaminated phase before the drops are added (no bubbles, sediment, or layering); the mixing motion reads as a rotation/swirl rather than shaking or tapping; the observation shot shows the tube unobstructed by any hand, finger, or label; the whole sequence plays out in one continuous shot without repositioning the tube or dropper.

Scientific and Causal Correctness rubric:
level_1: The tube's liquid looks identical in color before and after mixing; or the color shown contradicts how bromothymol blue behaves (e.g., a direct shift to red, or to purple, with no acid/base rationale).
level_2: A color appears, but it isn't one of bromothymol blue's three valid hues (yellow, green, or blue); or the color appears before the reagent is added or before mixing occurs; or the final color doesn't match the pH ~6.5–7.0 sample assumed for this demonstration (which should read green).
level_3: Color change happens after mixing and the final color is green, but at least one of the following breaks physical plausibility: the pre-addition urine color looks non-physiological (e.g., bright orange, cloudy white, fluorescent); the green appears before mixing finishes; the green fades or reverts within the observation window; or the green is patchy/streaked rather than uniform.
level_4: The green is uniform and stable across the whole liquid column for the observation period, and only appears once mixing is complete; the urine before mixing looks pale yellow (not colorless, not deep amber); the bromothymol blue reagent looks colorless or faintly yellow before it is added; no discoloration collects at the meniscus or tube wall.
level_5: All conditions for score 4 are met, and additionally: the pre-addition urine is pale yellow and clear; the three reagent droplets look clear with no visible dye streaking as they enter; the color shifts from pale yellow to a uniform green in one continuous transition immediately after mixing, without a lingering yellow-green intermediate band; the resulting green sits in the typical bromothymol-blue green range (neither noticeably teal-blue nor olive-yellow); no cloudiness or particulate appears at any point.

Spatiotemporal Consistency rubric:
level_1: The test tube appears mid-air with no placement action; the lighting jumps for no reason tied to the action; the liquid shoots upward against gravity; the tube twists or rotates on its own during mixing; the camera cuts between an extreme close-up and a wide shot with no motion bridging them.
level_2: The dropper tip touches the tube's rim or inner wall while dispensing; the swirling motion starts before the last droplet has landed; the observation beat begins before mixing has actually finished; the tube's tilt changes between the pre-addition and post-mixing shots with no visible transition; a reflection on the tube's glass appears or disappears between frames with no cause.
level_3: The tube stays put on a surface or in a steady hand; the three droplets fall straight down under gravity; the swirling motion looks smooth and continuous; the camera holds on the tube through the whole observation beat, apart from small, plausible imperfections such as a moment of motion blur that briefly obscures how many droplets have fallen.
level_4: All conditions for score 3 are met, and additionally: the tube keeps its vertical axis while being swirled rather than tipping erratically; each falling droplet keeps a coherent round shape rather than smearing or flattening; the dropper's silhouette never overlaps the tube's outline in a way that looks like it passed through the glass; the mixing motion never runs backward.
level_5: All conditions for score 4 are met, and additionally: the droplets appear to fall a little faster as they near the liquid surface rather than at a constant speed; the liquid's surface shows a believable meniscus curve both before and after the drops are added; the highlight on the tube's glass tracks smoothly with the tube's motion instead of jumping to a new spot; the swirling motion visibly winds up and settles rather than starting or stopping instantaneously.