Domain: Engineering — Food and Bioprocess Engineering
Target concept: Determination of Reducing Sugars in Food (Fehling's Reagent Method)

Video generation prompt: Take 2 mL of apple juice into a test tube, and add 1 mL of Fehling's reagent A and 1 mL of Fehling's reagent B, respectively. Heat the mixture in a boiling water bath for 2 minutes.

Evaluation guide:
(i) Target concept: Visual confirmation of reducing sugar detection via Fehling"s test requires causal linkage between sequential reagent addition and thermally triggered redox-driven precipitate formation.
Minimum mechanism: Apple juice must contain free aldehyde group (e.g., glucose); Fehling"s A (CuSO₄) and B (alkaline sodium potassium tartrate) must be added separately to prevent premature precipitation; boiling provides activation energy for electron transfer; Cu₂O formation is irreversible and visually definitive.
(ii)Storyline: [0–2s] Empty test tube centered; apple juice poured in → fills ~⅓ tube height. [2–4s] Blue reagent A poured → mixes, deepens blue. [4–6s] Colorless reagent B poured → solution homogenizes, remains deep blue. [6–10s] Tube lowered into vigorously boiling water bath (visible steam); solution transitions: blue → greenish-yellow cloudiness → localized brick-red granules forming at bottom → progressive upward spread of red precipitate while upper liquid stays translucent.

Manual:
Experimental Procedure
1. Add 2 mL apple juice to clean test tube.
2. Add 1 mL Fehling"s reagent A.
3. Add 1 mL Fehling"s reagent B.
4. Place tube in boiling water bath for heating.
Observation of Experimental Phenomena
Initial deep blue solution turns green/yellow, then forms brick-red precipitate during heating.
Summary of Experimental Principles
Reducing sugars (e.g., glucose in apple juice) reduce Cu²⁺ in alkaline tartrate complex (Fehling"s reagent) to Cu₂O, forming insoluble brick-red copper(I) oxide precipitate.

Prompt Grounding rubric:
level_1: No apple juice, no test tube, no Fehling"s reagent A or B visible; or none of the three core actions (adding juice, adding reagent A, adding reagent B) occur; or boiling water bath absent; or sequence is completely scrambled (e.g., heating before any addition).
level_2: At least one correct object present (e.g., test tube or apple juice) and one correct action occurs (e.g., liquid poured), but all three required additions (juice → A → B) are missing or misordered; boiling water bath not shown or replaced with unrelated heat source.
level_3: All three objects present: apple juice, test tube, Fehling"s reagents A and B (visually distinguishable by label or color convention); all three additions occur in correct order (juice first, then A, then B); boiling water bath appears with visible steam or bubbling water, but one of: reagent volumes not visually matched (e.g., A clearly more/less than B), or juice volume not plausibly ~2 mL (e.g., fills >½ tube or <¼ tube), or heating duration not implied by continuous immersion for full sequence.
level_4: All objects present and correctly labeled/identified by standard visual cues (apple juice amber-transparent, reagent A blue, reagent B colorless/clear, test tube cylindrical with rounded bottom, water bath with visible boiling); all three additions occur in strict sequence with clear separation (no simultaneous pouring); volume ratios visually consistent (juice ~2 mL, A ~1 mL, B ~1 mL; i.e., juice layer ~twice height of each reagent layer when added sequentially to same tube); boiling water bath fully frames tube mid-immersion for entire heating phase.
level_5: All conditions for score 4 met AND: (a) juice added first into empty test tube, (b) reagent A added second without spillage or overflow, (c) reagent B added third with identical volume appearance as A, (d) tube placed vertically into boiling water bath immediately after B addition, (e) no interruption, substitution, or cutaway during the entire sequence: single continuous shot or seamless cuts preserving spatial continuity and temporal order.

Scientific and Causal Correctness rubric:
level_1: No color change observed during/after heating; or precipitate absent; or final mixture remains fully transparent blue; or red precipitate appears before heating; or color change contradicts Fehling"s chemistry (e.g., turns green/yellow without red solid).
level_2: Color change occurs but is inconsistent with reducing sugar reaction: e.g., uniform orange/yellow solution without particulate formation; or red hue appears but remains fully soluble and homogeneous; or precipitate forms but is white/gray/black instead of brick-red.
level_3: Brick-red precipitate appears during or after heating; color change from initial deep blue (A+B mixed) to cloudy green/yellow intermediate then brick-red suspension is observable, but precipitate is not visibly settling or is fully dispersed without gravitational separation; or precipitate appears only after tube removal, not during heating.
level_4: Brick-red precipitate forms *during* heating in boiling water bath; initial mixture is homogeneous deep blue; intermediate green/yellow turbidity appears *before* red precipitate; precipitate is granular, non-dissolving, and visibly distinct from liquid phase; no incorrect side colors (e.g., no purple, brown, or black tints).
level_5: All conditions for score 4 met AND: (a) precipitate begins forming *while* tube is fully immersed in actively boiling water (steam bubbles visible at bath surface adjacent to tube), (b) precipitate is exclusively brick-red (no hue variation across particles), (c) precipitate particles are visibly coarse and settle downward under gravity *during* heating (i.e., lower portion of tube shows denser red accumulation while upper remains translucent), (d) no dissolution or fading of red color upon cessation of heating.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal rupture: test tube “teleports” between shots; reagents appear pre-mixed without addition; sudden lighting shift mid-sequence; tube deforms or rotates unnaturally; background changes discontinuously; steam appears before water bath is shown.
level_2: Moderate discontinuity: two or more of: (a) reagent bottles vanish/reappear between pours, (b) tube changes orientation (e.g., horizontal → vertical) without motion, (c) steam appears without visible water surface or heat source, (d) shadow direction flips between shots, (e) liquid level jumps without pouring motion.
level_3: Minor discontinuities present: one of (a) brief cut where tube is occluded during pour but reappears identically positioned, (b) slight focal shift during heating phase causing momentary blur, (c) ambient light flicker not tied to heat source, (d) tube wobble without structural violation; but all objects maintain fixed relative positions and no object violates physical persistence.
level_4: All objects maintain persistent identity, position, and orientation across all shots; no occlusion breaks object continuity; lighting and shadows remain consistent with single overhead/45° source; steam rises continuously and vertically from bath surface; tube remains vertically aligned and fully visible throughout heating; no warping, stretching, or morphing of test tube or liquids.
level_5: All conditions for score 4 met AND: (a) tube remains in fixed frame-centered position with no pan/tilt/zoom, (b) liquid meniscus remains stable and unbroken during all additions and heating, (c) steam flow is continuous, laminar, and uninterrupted for entire heating duration, (d) no inter-frame jitter, strobing, or motion blur violating natural hand-held or tripod stability, (e) reflection highlights on tube glass move coherently with lighting, not independently.