Domain: Natural Science — Chemistry
Target concept: Reaction of chlorine water with sodium bromide

Video generation prompt: Place several test tubes side by side. Add chlorine water to the test tube containing sodium bromide solution, then add carbon tetrachloride to induce phase separation.

Evaluation guide:
(i) Target concept: Oxidation-reduction driven solute partitioning across immiscible phases.
Minimum mechanism: Chlorine must be present as aqueous oxidant; bromide ions must be present in aqueous phase; elemental bromine must form and preferentially dissolve in carbon tetrachloride due to polarity mismatch and higher solubility; CCl4 must be denser than water to form lower layer; no chemical decomposition or side reactions occur.
(ii)Storyline: Frame 0–2: Static shot of three empty test tubes side-by-side. Frame 3–4: Sodium bromide solution added to middle tube (clear liquid, no color). Frame 5–6: Chlorine water added to same tube → aqueous layer acquires pale yellow tint. Frame 7–8: Carbon tetrachloride added → clear, dense liquid sinks below aqueous layer before mixing. Frame 9–10: Brief swirling motion → temporary emulsion. Frame 11–15: Rapid phase separation → sharp horizontal interface forms; lower layer uniformly orange/brown, upper layer fully colorless; view remains fixed frontal, full-tube height visible; no occlusion of interface or layers.

Manual:
Experimental Procedure
1. Place three clean test tubes side-by-side.
2. Add sodium bromide solution to the middle test tube.
3. Add chlorine water to the same test tube.
4. Add carbon tetrachloride to the same test tube.
5. Gently swirl to mix, then allow layers to separate.
Observation of Experimental Phenomena
- After chlorine water addition: aqueous layer turns pale yellow.
- After CCl4 addition and mixing: two immiscible layers form; lower layer becomes orange or brown; upper layer remains colorless.
Summary of Experimental Principles
Chlorine oxidizes bromide ions to elemental bromine (Cl2 + 2Br⁻ → 2Cl⁻ + Br2); bromine is more soluble in CCl4 than water, so it partitions into the denser CCl4 layer, producing orange-brown color.

Prompt Grounding rubric:
level_1: No test tubes appear on screen; the test tubes are not placed next to each other; none of the required bottles (chlorine water, sodium bromide solution, carbon tetrachloride) are shown; no liquid is ever added to any test tube.
level_2: At least one test tube appears, but it is not shown next to the others; only one of the three needed reagents is present (for example, just the chlorine water bottle); a liquid is poured, but onto the bench or somewhere other than into a test tube; carbon tetrachloride is never added.
level_3: Several test tubes are lined up next to each other in the same shot; a chlorine water bottle and a container of sodium bromide solution are both visible and easy to tell apart; chlorine water is poured into the tube already holding the sodium bromide solution; a carbon tetrachloride bottle is visible nearby but is not yet poured in.
level_4: The test tubes stay lined up next to each other; chlorine water is poured into the tube containing the sodium bromide solution; carbon tetrachloride is then visibly poured into that same tube; every needed object is present and easy to identify by its typical lab appearance.
level_5: All elements of score 4 are present AND: the test tubes are evenly spaced and fully visible in the foreground; the chlorine water bottle, sodium bromide solution, and carbon tetrachloride bottle are each clearly recognizable; chlorine water is poured in first, carbon tetrachloride second, both into the same tube; nothing extra blocks the view of either pour.

Scientific and Causal Correctness rubric:
level_1: No color ever appears in the sodium bromide tube; no two liquid layers ever form; the liquid in the tube stays a single uniform phase with no separation, even after both reagents have been added.
level_2: A color appears, but not where it should: for example, the color shows up in the upper aqueous layer instead of the lower CCl4 layer, or a phase separation happens with no color at all, or a yellow/orange tint appears before the chlorine water has even been added.
level_3: After chlorine water is added, the aqueous solution in the tube turns pale yellow; after carbon tetrachloride is added, two distinct horizontal layers form in that tube: the upper layer pale yellow or colorless, the lower layer orange or brown; the two layers do not remix once separated, and the color stays only in the lower layer.
level_4: All elements of score 3 are present AND: the pale-yellow tint appears in the aqueous layer right after the chlorine water is added, before CCl4 goes in; the two layers separate cleanly within the same tube after the CCl4 addition; the lower layer is clearly orange or brown while the upper stays colorless or pale yellow; no orange/brown tint remains in the upper layer once the tube has settled.
level_5: All elements of score 4 are present AND: the sodium bromide solution starts fully colorless; the chlorine water addition gives it only a subtle pale-yellow tint; after the carbon tetrachloride addition and a brief swirl, the two layers separate quickly into a sharp, well-defined boundary; the upper layer ends up completely colorless and see-through, the lower layer a uniform, opaque orange-brown; no blurring, streaking, or color creeping across the boundary between the layers.

Spatiotemporal Consistency rubric:
level_1: A test tube's position or size on screen suddenly changes between frames with no visible cause; the room lighting changes with nothing to explain it; a test tube's shape visibly distorts partway through the clip; a liquid layer appears without any prior pouring or mixing; the carbon tetrachloride is seen inside the tube before its bottle is ever shown near it.
level_2: One or more of the test tubes blinks out of view and back in; the pouring motion looks broken, e.g., the hand disappears mid-pour; the two liquid layers separate instantly with no swirling or settling shown or implied beforehand; the lighting shifts noticeably between the two additions; something in the background shifts position relative to the test tubes.
level_3: Every test tube stays in the same place and orientation for the whole clip; the hand enters the frame from the same direction for both the chlorine water and the carbon tetrachloride additions; no test tube blinks out or reappears; any swirling shown is continuous and looks like a natural hand motion; the lighting stays the same throughout; the glass walls and liquid surfaces do not warp or stretch.
level_4: All elements of score 3 are present AND: the test tubes keep the same spacing and alignment relative to each other across the whole clip; each pour is smooth and continuous, ending with the liquid landing inside the target tube; any swirling motion is brief, stays contained to that one tube, and looks like a natural hand movement; there is no visible jitter, lens warping, or shadow that suddenly looks different from one frame to the next.
level_5: All elements of score 4 are present AND: the test tubes' positions, sizes, and angles look the same across every frame, with no visible drift; each pour follows a single smooth path with no hesitation, backtrack, or overshoot; any swirling is one continuous motion (roughly one to two full rotations) without pausing or jerking; the lighting, shadows, and reflections on the glass stay physically consistent and steady; the test tubes in front and the background behind them do not appear to shift relative to each other.