Domain: Natural Science — Chemistry
Target concept: Determination of Moisture in Chemical Raw Materials (Karl Fischer Colorimetric Method)

Video generation prompt: Take 1 mL of the methanol sample and place it in a dry test tube, then add 2 drops of Karl Fischer reagent.

Evaluation guide:
(i) Target concept: Visual confirmation that Karl Fischer reagent's own amber-brown iodine color persists after mixing into an already largely anhydrous methanol sample, rather than fading -- the colorimetric signal used to judge low moisture content.
Minimum mechanism: The methanol must start colorless and transparent; the Karl Fischer reagent must visibly be amber-brown before it ever touches the liquid; each of the two drops must actually merge into the bulk methanol (not just touch the surface) before any color change is judged; because the sample is close to anhydrous, only a negligible share of the reagent's iodine reacts with residual water, so the resulting tint stays in the amber-brown family and does not fade back to colorless or shift to an unrelated hue.
(ii) Storyline: Frame 1-3: Static shot of empty dry test tube on bench. Frame 4-6: Pipette delivers ~1 mL methanol into the tube -- the liquid forms a concave meniscus and stays colorless. Frame 7-8: Dropper approaches from upper right, pauses above the tube opening. Frame 9: First amber-brown drop detaches and falls into the tube, beginning to disperse as a faint brown streak through the still mostly clear liquid. Frame 10: Second drop detaches and enters; once both drops have mixed through the liquid, the whole column settles into one light, even amber-brown tint that holds steady rather than fading further. Perspective: Fixed frontal close-up (tube occupies >=60% of frame height), no cutaways, no POV shift, full visibility of tube interior and droplet trajectory.

Manual:
Experimental Procedure
1. Place a dry test tube upright on bench.
2. Using a graduated pipette, transfer 1 mL of methanol sample into the test tube.
3. Using a clean dropper, add exactly 2 drops of Karl Fischer reagent into the test tube.
Observation of Experimental Phenomena
Methanol is initially colorless and transparent. The Karl Fischer reagent itself is amber-brown due to dissolved iodine. After the 2 drops disperse through the methanol, the liquid takes on a light, even amber-brown tint that persists rather than fading, consistent with the sample containing little to no reacted moisture.
Summary of Experimental Principles
The Karl Fischer colorimetric method relies on the stoichiometric, redox consumption of iodine by water: reagent contains iodine, sulfur dioxide, a base (e.g., pyridine or imidazole), and methanol as solvent. Iodine gives the reagent its amber-brown color; where trace water is present, iodine is reduced (consumed) and the brown color fades toward pale yellow or colorless in proportion to the moisture reacted. When only a very small amount of water is present, as expected for a compliant methanol raw material, only a negligible fraction of the added iodine is consumed, so the reagent's own amber-brown color persists after mixing -- this persistence, rather than a shift to any other hue, is the visual signal of low moisture content.

Prompt Grounding rubric:
level_1: None of the three required setup elements are shown together: no dry test tube, no methanol being measured into it, and no Karl Fischer reagent dropper or bottle; the reagent-addition action described in the prompt never happens.
level_2: Only one or two of the three elements appear, and at least one is the wrong kind of object -- for example the tube already holds a cloudy or colored liquid instead of colorless methanol, or the dropper/bottle is generic and not recognizable as a reagent dispenser -- and no methanol-then-reagent sequence plays out.
level_3: A dry test tube receives roughly 1 mL of colorless methanol first, then a dropper adds drops of Karl Fischer reagent from a visually distinct bottle; methanol is added before the reagent as in the prompt, and about two drops are dispensed into the tube.
level_4: Everything required for the 3-point level is present, and in addition the test tube stays in the same position and orientation for the whole clip, the dropper always approaches from one consistent direction, both drops land inside the tube opening rather than on the rim or bench, and methanol is never added a second time or after the reagent.
level_5: Everything required for the 4-point level is present, and in addition exactly one test tube, one methanol source, and one Karl Fischer reagent dropper are visible at any time, the methanol level is consistent with about 1 mL (a visible meniscus well below the rim), and exactly two distinct drops leave the dropper tip and enter the liquid -- no third drop, no drops merging in mid-air, and no moment where the drop count is hidden from the camera.

Scientific and Causal Correctness rubric:
level_1: No color relationship between reagent and liquid appears at all: the liquid stays perfectly colorless even after both drops enter, or it takes on a color with no basis in Karl Fischer chemistry (blue, green, or violet), or the liquid was already brown before any reagent touched it.
level_2: A color appears but the sequence or physics is implausible: the liquid changes color before the second drop actually reaches it, the whole column changes instantly the moment a drop merely nears the surface, or bubbling/precipitate appears instead of a simple color change.
level_3: The color that develops is the reagent's own amber-brown: each drop looks amber-brown as it falls, and once both drops have mixed through the roughly 1 mL of methanol, the liquid settles into a light, even amber-brown tint that persists rather than fading back toward colorless, reflecting that the largely anhydrous methanol reacts with only a negligible share of the reagent's iodine.
level_4: Everything required for the 3-point level is present, and in addition the amber-brown tint is even throughout the liquid with no streaking or a darker band near the surface, the tint stabilizes within a few frames of the second drop mixing in and neither keeps darkening nor fades afterward, and the liquid stays clear rather than turning cloudy.
level_5: Everything required for the 4-point level is present, and in addition no tint appears until a drop has actually merged into the bulk liquid (not while still falling or only touching the surface), the final hue clearly belongs to the same amber-brown family as the reagent drops themselves and never shifts toward pink, red, violet, or green, and this persisting tint is the only color event in the whole clip.

Spatiotemporal Consistency rubric:
level_1: The test tube's position or apparent size changes abruptly between shots with no hand visibly moving it, or it rotates more than about 30 degrees with no visible hand motion; the dropper or its bottle appears or vanishes from one frame to the next instead of entering the frame; the overall lighting or color cast of the scene switches suddenly (e.g., bright to dark) partway through; or background elements flicker or warp instead of staying stable.
level_2: The test tube stays in view but jumps sideways by more than about a third of its height, or rotates sharply, within a single cut with no in-between motion; a falling drop skips straight from the dropper tip into the liquid with no visible arc or fall; a hand's shadow disappears and reappears inconsistently; or the highlight on the glass shifts from one side of the tube to the other with no corresponding movement of the light, hand, or camera.
level_3: The test tube stays upright in the same spot for the whole clip, its glass walls stay continuous and undistorted, the lighting stays at a steady level throughout, and both the dropper's approach and each drop's fall read as continuous motion rather than instant jumps.
level_4: All conditions for the 3-score level are met; additionally, the methanol-filling step and the two reagent-drop additions read as clearly separate events with their own visible start and finish rather than blurring together, no frame is skipped or repeated in a way that makes the drop count ambiguous, and the tube's size and position relative to the frame stay constant as the hand and dropper move near it.
level_5: All conditions for the 4-score level are met; additionally, each drop is visibly forming at the dropper tip (a bulge that narrows before separating) and falls as one coherent, roughly round drop rather than a smear or instant dot, the tube's base stays visible and resting on the bench the whole time, and no cut or occlusion ever hides the instant a drop leaves the dropper or lands in the liquid.