Domain: Natural Science — Chemistry
Target concept: Ligand exchange of cobalt(II) complexes leads to visible color changes (water vs. chloride...)

Video generation prompt: A transparent glass beaker contains a water-soluble cobalt(II) salt; concentrated hydrochloric acid is added first, followed by the addition of water while stirring.

Evaluation guide:
(i) Target concept: Ligand exchange equilibrium in cobalt(II) complexes ([Co(H₂O)₆]²⁺ ⇌ [CoCl₄]²⁻ + 4H₂O) driven by chloride concentration.
Minimum mechanism: Presence of aqueous Co²⁺, sufficient Cl⁻ from concentrated HCl to form blue [CoCl₄]²⁻, and subsequent dilution to shift equilibrium left and regenerate pink [Co(H₂O)₆]²⁺; no competing ligands (e.g., NH₃) or redox agents present.
(ii)Storyline: Frame opens on static shot of beaker with pale pink/colorless solution → concentrated HCl added (visible stream) → blue color emerges and spreads uniformly through solution during stirring → water added (distinct stream) → pink color emerges and replaces blue uniformly during continued stirring → final stable pink state held for ≥1 second. Perspective: fixed frontal/slightly angled view; beaker fully in frame; all actions occur within beaker volume; no cuts or camera repositioning; lighting stable and diffuse to ensure color fidelity.

Manual:
Experimental Procedure
1. Place transparent glass beaker containing colorless/pale pink aqueous cobalt(II) salt solution on surface.
2. Add concentrated hydrochloric acid dropwise while stirring → solution turns deep blue.
3. Add distilled water while stirring → solution turns pink/rose.
Observation of Experimental Phenomena
Initial solution is colorless or pale pink; after HCl addition, uniform deep blue color appears; after water addition, uniform pink/rose color replaces blue.
Summary of Experimental Principles
Cobalt(II) ions form [Co(H₂O)₆]²⁺ (pink) in water; in excess Cl⁻, they form tetrahedral [CoCl₄]²⁻ (blue); dilution shifts equilibrium back to aquo complex.

Prompt Grounding rubric:
level_1: No transparent glass beaker appears; no pink or colorless cobalt(II) solution is visible at the start; concentrated hydrochloric acid is never added; water is never added; or no stirring of any kind is shown.
level_2: A transparent glass beaker holding some liquid is present, but the starting liquid is not colorless or pale pink; only one of the two additions (acid or water) occurs while the other is missing; stirring never happens or cannot be identified; or the water is poured in before the acid.
level_3: A transparent glass beaker holds a colorless or pale-pink aqueous solution; a stream of concentrated hydrochloric acid is added first; a stream of water is added second; stirring is visible during or after at least one of the two additions; every object appears and the two additions occur in the correct order.
level_4: Everything described at the 3-point level holds, and the two additions are visually distinguishable from each other by how they enter the beaker (for example a dropper for the acid versus a cup pouring the water) or by a visible label on the source container; stirring is continuous and clearly aimed at the beaker's contents through both additions.
level_5: Everything described at the 4-point level holds, and the beaker stays fixed in the same spot in the frame; both liquids are poured from off-screen sources that keep the same side and height relative to the beaker across both additions; the stirring rod is visible entering and leaving the frame only near the top of the beaker, never disappearing mid-stir; nothing blocks the view of either addition.

Scientific and Causal Correctness rubric:
level_1: The solution never changes color and stays colorless or pale pink the whole time; or it turns blue with no hydrochloric acid having been added; or it turns pink with no water having been added; or the two color changes happen in the wrong order.
level_2: A color change happens, but the direction is backwards — the solution turns blue after the water is added, or turns pink after the acid is added; or the color change is not tied to either addition event; or the ending color is wrong (for example still blue after water has been added).
level_3: The solution starts colorless or pale pink, turns clearly blue during or right after the concentrated hydrochloric acid goes in, then turns clearly pink during or right after the water goes in; each color is stable and identifiable on its own, without extended flickering between the two hues.
level_4: Everything described at the 3-point level holds, and the blue color is fully and evenly developed before the water addition begins; the pink color is fully and evenly developed once the water addition finishes; there is no lingering patch of unmixed blue sitting under or beside the new pink liquid.
level_5: Everything described at the 4-point level holds, and the color changes track the moment of contact closely: no color shift appears before the first drop of a reagent touches the solution, and none lingers long after an addition ends; the final pink has no leftover blue tinge, the blue phase has no premature pink tinge, and both hues look like the expected saturated blue of [CoCl4]2- and saturated pink of [Co(H2O)6]2+ rather than an off-shade such as purple, green, or orange.

Spatiotemporal Consistency rubric:
level_1: The beaker vanishes and reappears; the liquid's surface height changes with no addition shown to explain it; the color flips in a single full-frame flash with no pour or stir causing it; the stirring rod disappears mid-stir; or the lighting on the scene swings dramatically between one frame and the next.
level_2: The beaker's position drifts sideways or up/down by roughly its own width or height between the two additions; the stirring motion freezes for a stretch and then resumes with no cause; the color change happens across only a couple of frames with no visible mixing motion behind it; or a poured liquid stream behaves impossibly (flowing upward, splitting apart in mid-air).
level_3: The beaker stays in one place; the liquid surface moves continuously while being stirred; each poured liquid follows a smooth downward path into the beaker; the two color changes each unfold over several consecutive frames with visible mixing (a blue cloud spreading, a pink front advancing) rather than snapping to the new color; neither the beaker nor the rod disappears or warps.
level_4: Everything described at the 3-point level holds, and the stirring keeps a consistent speed and direction across both additions; the poured liquids keep a coherent stream shape rather than splattering or misting apart; no sudden light or shadow change crosses the beaker's surface during either addition.
level_5: Everything described at the 4-point level holds, and the liquid's meniscus keeps a physically sensible curve throughout; the stirring rod tip and the edge of each poured stream move smoothly with no visible flicker or ghosting from frame to frame; stirring never appears before its addition has started or stops before the addition has finished; the way the beaker wall and the liquid surface shift together under the fixed viewpoint stays consistent throughout.