Domain: Natural Science — Chemistry
Target concept: The equilibrium color change of cobalt chloride upon heating and cooling in a water bath

Video generation prompt: A transparent test tube containing a cobalt chloride solution with excess concentrated hydrochloric acid added is alternately placed in a hot water bath and a cold water bath, with the solution clearly visible as it moves between the two water baths.

Evaluation guide:
(i) Target concept: Reversible, temperature-dependent chloride-for-water ligand exchange equilibrium in an aqueous cobalt(II) chloride solution containing excess chloride ion.
Minimum mechanism: Sufficient free chloride ion (from the added hydrochloric acid) must be present alongside water molecules for the equilibrium to shift visibly with temperature; no irreversible decomposition or precipitation occurs; the solution stays homogeneous and transparent throughout.
(ii)Storyline: Frame 0–2: Tube with pink/magenta solution enters view, stationary above the hot bath. Frame 3–5: Tube lowers into the hot bath; full submersion achieved; color shifts from pink/magenta toward blue within a few frames. Frame 6–7: Tube lifts fully out, held in air; blue color persists briefly. Frame 8–10: Tube lowers into the cold bath; full submersion achieved; color shifts back to pink/magenta. Frame 11–12: Tube held in the cold bath; pink/magenta color stable. Perspective: Fixed frontal close-up, centered on tube and both baths side-by-side; no camera motion; full tube and bath rims always in frame; no occlusion by hands or tools after initial placement.

Manual:
Experimental Procedure
1. Fill a transparent test tube with a cobalt chloride solution containing excess concentrated hydrochloric acid (pink/magenta at room temperature).
2. Place the tube fully into the hot water bath → observe the color shift toward blue.
3. Remove the tube and place it fully into the cold water bath → observe the color shift back to pink/magenta.
4. Repeat the alternation once more for clarity.
Observation of Experimental Phenomena
The cobalt chloride solution reversibly shifts between blue (in the hot bath) and pink/magenta (in the cold bath); the color change is rapid and tracks the bath temperature.
Summary of Experimental Principles
In aqueous solution with excess chloride ion, cobalt(II) exists in equilibrium between the pink hexaaquacobalt(II) ion [Co(H2O)6]2+ and the blue tetrachlorocobaltate(II) ion [CoCl4]2-. This ligand-exchange equilibrium is endothermic in the forward (blue-forming) direction, so heating shifts it toward the blue complex, while cooling shifts it back toward the pink complex.

Prompt Grounding rubric:
level_1: No transparent test tube is shown, no cobalt chloride solution is visible, and neither a hot water bath nor a cold water bath container appears; the tube is never placed into any bath; none of the objects or actions described in the prompt are present.
level_2: A test tube and at least one water bath container appear, but the tube's liquid is not visibly colored, or the tube is never moved between two baths; only one bath type (hot or cold) is present, or the tube is never actually immersed in a bath, so the alternation sequence cannot be identified.
level_3: A transparent test tube holding a colored solution appears together with two visually distinct water baths (for example, one showing steam or warmth cues, the other showing an unheated or chilled appearance); the tube contacts one bath and later the other, so the order of contact is identifiable, but at least one transition is abrupt or unclear, such as the tube appearing already in the second bath with no visible movement between the two.
level_4: The transparent test tube, its cobalt chloride solution, and both the hot and cold water baths are all present and visually distinguishable from one another; the tube is placed into one bath, fully removed, and then placed into the other bath as three separate, clearly ordered events; the tube never appears in both baths at once and is never duplicated.
level_5: Everything required for a 4 holds, and in addition the tube visibly travels between the two baths along a continuous path with no jump cuts; both baths stay in the same fixed positions in the frame throughout; the tube stays fully visible and centered during every placement and removal; no hand, tool, or extra object obscures the tube or baths at any point.

Scientific and Causal Correctness rubric:
level_1: The solution shows no color change at all, or changes to a hue other than pink/magenta or blue (for example green or yellow), or a color change happens while the tube is in air or unchanged within a single bath; there is no visible link between which bath the tube is in and which color appears.
level_2: A color change is visible, but its direction is reversed from the real cobalt chloride equilibrium (the solution turns pink/magenta in the hot bath and blue in the cold bath), or only one of the two colors ever appears, so the hot and cold states cannot be told apart by color.
level_3: The solution turns blue while the tube is in the hot bath and pink/magenta while the tube is in the cold bath, matching the real chloride-complex equilibrium; each color stays stable while the tube remains in that bath, but the color change lags noticeably (more than about a second) after the tube is fully immersed rather than beginning close to the moment of contact.
level_4: The solution is blue only while in contact with the hot bath and pink/magenta only while in contact with the cold bath, with no leftover pink tint in the hot-bath frames or blue tint in the cold-bath frames; the color begins changing promptly after the tube enters each bath rather than after a long delay.
level_5: Everything required for a 4 holds, and in addition each color (blue in the hot bath, pink/magenta in the cold bath) stays fully saturated with no hazy, gray-violet, or lavender in-between hue lingering in any frame; the switch from one color to the other tracks bath contact closely and consistently in both directions across every repetition shown.

Spatiotemporal Consistency rubric:
level_1: The test tube or a water bath drops out of one frame and shows up again later in a different spot; the two baths swap positions in the frame; the room lighting jumps between clearly different states with no transition; motion freezes for a noticeable stretch of the video; the tube's shape visibly warps or stretches.
level_2: The tube's orientation changes inconsistently between the two bath contacts, such as upright in one and tilted in the other with no visible cause; one of the two baths is missing for part of the video and then reappears; the shadow cast by the tube or baths changes direction between frames with no change in the light source; the tube's path between baths skips, appearing near the hot bath in one frame and already fully inside the cold bath in the next with no visible travel.
level_3: The tube looks slightly different in size between the hot-bath and cold-bath shots; the shadows are mostly steady but show a small, noticeable misalignment; the tube shows minor jitter while held still; the overall motion has at most one small hiccup, such as a single skipped or repeated moment during a transition, without any larger break in the scene.
level_4: The test tube, both water baths, and the surrounding bench stay the same size, shape, and position across all frames; the tube moves along one smooth, continuous path between the two baths; shadows stay attached to the objects casting them and pointed in one consistent direction; no object duplicates, disappears, or changes shape unexpectedly; the video shows no sudden flashing or strobing.
level_5: Everything required for a 4 holds, and in addition the tube's speed of movement looks even rather than jerky, with no sudden speeding up or stopping; the tube keeps the same apparent distance from the camera and the same relationship to the background throughout; the edges of the tube and baths stay sharp and free of smearing during motion, so the whole scene reads as one continuous, physically coherent take.