Domain: Healthcare — Pharmaceutical Chemistry
Target concept: Assay of Aspirin Purity (Ferric Chloride Colorimetric Method)

Video generation prompt: Place the aspirin sample in a test tube, add ethanol to dissolve it, then add a few drops of ferric chloride solution while gently shaking. Clearly demonstrate the correct order of adding the test tube, pipette, and reagents, focusing solely on the sequence of operations.

Evaluation guide:
(i) Target concept: Colorimetric purity screening of an aspirin sample using the ferric chloride (FeCl₃) test, which detects free salicylic acid (a phenolic impurity from incomplete acetylation or storage hydrolysis) rather than confirming aspirin's identity outright; the promptness and intensity of any violet color reflects how much free salicylic acid is present, with a highly pure sample expected to show only faint or no color under the same conditions.
Minimum mechanism: Solid aspirin must be fully dissolved in ethanol before ferric chloride is added, since Fe³⁺ cannot react with an undissolved solid; the FeCl₃ solution must contact the dissolved sample and be mixed by gentle shaking; any violet color that develops comes from free phenolic –OH groups (already present in the sample as a salicylic acid impurity) binding Fe³⁺; it is not produced by ethanol hydrolyzing the aspirin during the demonstration; no color should appear before both the dissolution step and the ferric chloride addition have occurred.
(ii)Storyline: [Frame 0–2] Solid aspirin placed into stationary test tube → [Frame 3–5] Ethanol dispensed from pipette into tube, meniscus rises, solid disappears (full dissolution confirmed visually) → [Frame 6–8] Ferric chloride dispensed from pipette into same tube → [Frame 9–10] Immediate gentle shaking motion begins → [Frame 11–12] A violet color consistent with the sample's free salicylic acid content emerges uniformly in the liquid phase, confined to solution, with no color on tube walls or undissolved matter; all events occur from fixed frontal viewpoint with consistent lighting and no cuts or repositioning.

Manual:
Experimental Procedure
1. Place solid aspirin sample into a clean test tube.
2. Add ethanol using a pipette until aspirin dissolves completely.
3. Add 1–2 drops of ferric chloride solution using a pipette while gently shaking the test tube.
Observation of Experimental Phenomena
A violet color develops in the solution after ferric chloride addition and shaking, with its intensity reflecting the level of free salicylic acid impurity in the sample.
Summary of Experimental Principles
Acetylsalicylic acid's phenolic –OH group is acetylated and does not itself react with Fe³⁺. Aspirin samples can contain a small amount of free salicylic acid as a residual impurity from incomplete synthesis or from slow hydrolysis during storage. Dissolving the sample in ethanol brings any such free salicylic acid into solution, where its unmasked phenolic –OH binds Fe³⁺ from the ferric chloride to form a violet-colored complex — so color intensity indicates impurity level (purity), rather than merely confirming that the sample is aspirin.

Prompt Grounding rubric:
level_1: None of the three core objects (test tube, aspirin sample, and ferric chloride solution) appears in the scene; or the test tube, aspirin, ethanol, and ferric chloride are never brought into any functional relationship with each other (e.g., no dispensing action of any kind is shown).
level_2: A test tube is visible, but ethanol and ferric chloride solution are not shown being added to it; or a pipette never contacts the test tube; or the order of additions is fully reversed (e.g., ferric chloride is dispensed before the aspirin is placed in the tube or before ethanol is added).
level_3: Test tube, solid aspirin, ethanol, ferric chloride solution, and pipette are all visible; aspirin goes into the tube first, ethanol second, and ferric chloride third; but at least one addition lacks clear visual evidence of contact (e.g., the pipette tip never visibly enters the tube, or liquid does not visibly enter the tube for one of the additions).
level_4: Test tube, solid aspirin, ethanol, and ferric chloride solution are all clearly visible and correctly identified; aspirin is placed into the test tube first, ethanol is dispensed into the same tube second, and ferric chloride is dispensed into the same tube third; each addition shows unambiguous contact between the pipette/liquid and the tube's contents; the tube and its contents remain the same object throughout (no substitution or duplication).
level_5: All conditions for score 4 are met, and additionally: the gentle shaking motion is clearly shown immediately after the ferric chloride addition; the test tube stays in the same general position and orientation across all three additions; no extra test tubes, reagent containers, or hands appear beyond what the procedure requires; there is no visible jump in the tube's contents or position between the addition steps.

Scientific and Causal Correctness rubric:
level_1: No color change occurs at any point; or a violet color appears before the ferric chloride has been added; or a violet color appears while the aspirin is still visibly undissolved (solid particles present); or ferric chloride is added and mixed but the solution never develops any color at all.
level_2: The solution changes to a color other than violet/purple (e.g., blue, green, yellow, or no hue shift beyond the reagents' own tint); or a violet tint appears in the tube before the ethanol has fully dissolved the aspirin; or a violet tint appears in a region of the liquid that never received ferric chloride.
level_3: A violet color appears only after the ferric chloride has been added, and only after the aspirin has visibly dissolved in the ethanol; however, the color appears without any visible shaking/mixing afterward, or persistent undissolved solid is still visible in the tube when the color appears.
level_4: A violet color appears only after both the aspirin has fully dissolved and ferric chloride has been added, and only once gentle shaking has visibly mixed the solution; the color is confined to the liquid itself, not appearing on the tube walls or on any undissolved particles; no violet appears anywhere in the tube before dissolution, ferric chloride addition, and shaking have all occurred.
level_5: All conditions for score 4 are met, and additionally: the violet color builds up gradually over roughly a second or two of shaking rather than flashing on instantaneously; the color is spatially uniform through the liquid with no patchy or streaky regions; no violet tint appears anywhere the ferric chloride solution did not reach; the depicted color response is consistent with revealing free salicylic acid impurity in the sample rather than being an arbitrary reagent-mixing color.

Spatiotemporal Consistency rubric:
level_1: The test tube is missing from the frame for part of the sequence and then reappears in a different spot with no motion connecting the two positions; the aspirin solid jumps directly from an off-screen location into the tube without any visible path; the pipette appears already inside the tube or vanishes from view without any approach or withdrawal motion; a liquid stream appears floating in mid-air with no visible connection to the pipette tip; the overall brightness or color tone of the shot changes suddenly with no visible cause.
level_2: The test tube's position or tilt changes noticeably between steps without any hand touching it; the pipette appears to move on its own with no visible hand holding it; the ethanol or ferric chloride stream begins before the pipette tip has reached the tube opening; the shaking motion starts before the pipette has been withdrawn from the tube.
level_3: The test tube stays in a consistent spot in the frame (centered or to one side) throughout all three additions; the pipette approaches the tube from roughly the same direction and angle for each addition; the ethanol and ferric chloride streams visibly originate at the pipette tip and end inside the tube; the shaking motion is a continuous, tube-centered back-and-forth rather than a sudden displacement.
level_4: All conditions for score 3 are met, and additionally: the lighting and shadow beneath the test tube look the same across all three additions; the tube's wall thickness and curvature look consistent from shot to shot; the liquid's meniscus forms naturally right after each addition rather than jumping to its final level; the pipette is fully withdrawn from the tube before the next reagent is added; the shaking motion has a steady, moderate rhythm that does not splash liquid out of the tube.
level_5: All conditions for score 4 are met, and additionally: the test tube's position and size stay visually identical across every frame of all three additions and the shaking; no blurring hides the moment the pipette tip meets the liquid surface; the background behind the tube does not shift relative to the tube as the camera view stays fixed; no reflections in the glass duplicate or invert any object in the scene; every motion (placing the aspirin, dispensing each liquid, and shaking) looks smooth and physically continuous from start to finish.