Domain: Natural Science — Chemistry
Target concept: Test for Fe³⁺ Ions

Video generation prompt: A test tube contains an appropriate amount of iron(III) chloride solution. A few drops of potassium thiocyanate (KSCN) solution are added to the solution in the test tube.

Evaluation guide:
(i) Target concept: Formation of a coordination complex between Fe³⁺ and SCN⁻ yielding a chromophoric species with diagnostic red color.
Minimum mechanism: Aqueous dissociation of FeCl₃ yields free Fe³⁺; aqueous dissociation of KSCN yields free SCN⁻; rapid ligand substitution forms octahedral [Fe(SCN)(H₂O)₅]²⁺ in solution; a ligand-to-metal charge-transfer (LMCT) transition in this complex absorbs strongly in the blue-green region of the visible spectrum, so the light that reaches the eye appears red.
(ii)Storyline: Frame 0–2: Static shot of test tube with pale yellow solution, centered, fixed viewpoint, stable lighting. Frame 3–5: Dropper enters top of frame, aligns vertically over tube opening, remains stationary for ≥1 frame. Frame 6–7: First drop detaches and descends visibly; impact at liquid surface is resolved. Frame 8–10: Red color initiates at impact point and expands uniformly to fill entire solution volume; final frame shows homogeneous blood-red liquid with no residual yellow. Throughout: no occlusion of tube, no camera motion, no secondary objects entering scene.

Manual:
Experimental Procedure
1. A clean, transparent test tube contains a pale yellow aqueous iron(III) chloride solution.
2. A dropper dispenses 2–4 drops of colorless potassium thiocyanate (KSCN) solution into the test tube.
Observation of Experimental Phenomena
The pale yellow solution instantly turns uniform, transparent, blood-red upon addition of KSCN.
Summary of Experimental Principles
Fe³⁺ ions react with SCN⁻ ions to form the soluble complex ion [Fe(SCN)]²⁺, which has an intense blood-red color — a highly sensitive and specific test for Fe³⁺.

Prompt Grounding rubric:
level_1: No test tube is visible; no pale-yellow iron(III) chloride solution is present; no KSCN dropper or vial appears; no drop is ever added; the tube is empty or absent from frame.
level_2: The test tube holds some liquid, but its identity is unclear (it looks solid, opaque, or is simply absent); the KSCN dropper or vial never appears; no drop-adding action occurs; only one reagent is ever implied to exist.
level_3: The test tube contains a clear, pale-yellow liquid consistent with an FeCl₃ solution; a separate KSCN dropper or small vial is visible; the dropper tip contacts or enters the test tube's mouth; at least one drop visibly leaves the dropper and enters the tube; no reagent stands in for the wrong vessel (e.g., a beaker used instead of the test tube).
level_4: All core objects appear together and correctly typed: a transparent test tube, a pale-yellow FeCl₃ solution filling roughly a third to half of the tube, a clearly separate KSCN dropper bottle, the dropper held above the tube's mouth, and one or more discrete drops visibly leaving the dropper tip and entering the solution; nothing is substituted, such as a spray bottle, a powder scoop, or a pipette mislabeled as a syringe.
level_5: The test tube has a rounded-bottom cylindrical shape and glass-like transparency; the FeCl₃ solution fills roughly one third to one half of the tube with a uniform pale-yellow tint; the KSCN solution sits in a distinctly labeled dropper bottle with visible liquid inside; the dropper is held vertically with its tip aligned over the tube's opening; two to four separate, rounded drops are visible either falling through the air or merging with the liquid surface.

Scientific and Causal Correctness rubric:
level_1: The liquid never changes color at any point in the clip; it stays colorless, pale, or whatever hue it started as; no red or blood-red tone ever appears; if the starting solution is already the wrong color (e.g., dark brown or orange instead of pale yellow), it simply stays that wrong color.
level_2: The starting liquid is correctly pale yellow (consistent with an FeCl₃ solution), but adding the KSCN drops produces no visible color change; or the resulting color is wrong for this reaction (e.g., blue, green, purple, black, or milky white instead of red); or a red tint shows up before any drop has touched the liquid.
level_3: The starting liquid is pale yellow; once the KSCN drops are added, the solution turns a uniform red or blood-red throughout; the red color does not fade back toward yellow before the clip ends; no bubbling, cloudy precipitate, or separate layers accompany the color change.
level_4: The starting liquid is pale yellow and clear; the red color appears only once a drop has actually reached the liquid surface, never earlier; it spreads outward and downward from where the drop landed until the whole solution looks evenly red; nothing else competes with this change — no cloudiness, no layering, no streaky or patchy coloring.
level_5: The pale yellow solution looks calm and even before any drop lands; each drop that lands produces a deep-red patch right at that spot almost immediately; the red spreads outward from each impact point as though mixing into the surrounding liquid; by the final frame the whole tube looks like one uniform, clear, intense blood-red solution with no yellow patches left, no uneven blotches, and no moment where the color reverts or flickers back toward yellow.

Spatiotemporal Consistency rubric:
level_1: The test tube vanishes from view or reappears in a different spot; the pale-yellow liquid's level jumps with no drop having entered; the dropper appears already inside the tube with no approach shown; the overall scene brightness flips between light and dark from one frame to the next; the tube's outline suddenly bends or warps.
level_2: The test tube stays visible but its size or proportions shift inconsistently between frames; the liquid level changes with nothing added to explain it; the dropper enters from off-frame already touching the liquid, skipping any downward travel; the red color appears before the drop touches the surface, or lingers after the dropper is withdrawn with no clear cause.
level_3: The test tube stays in the same place and orientation for the whole clip; the pale-yellow liquid surface is calm and unchanging before the drop falls; the dropper's descent toward the tube's opening is continuous and visible; each drop follows a plausible falling path; the red color only begins once a drop actually touches the liquid, then spreads outward without jumping across empty space.
level_4: The test tube, dropper, and liquid keep consistent position, size, and orientation across the whole clip; the tube wall and liquid surface never stretch, bend, or shear; the dropper's motion is steady and aimed straight down at the tube's opening; each drop keeps a rounded shape while falling; the red color spreads in the direction the liquid would naturally move, without being clipped at the tube's edge or cut off mid-frame.
level_5: No spatial or timing errors appear anywhere in the clip: the test tube's outline stays in the same place and shape from the first frame to the last; the curve of the liquid surface changes smoothly as red spreads through it; the dropper tip stays aligned directly above the tube's opening throughout; each drop visibly accelerates and flattens slightly on contact with the liquid; the red color spreads outward from each impact point in a pattern consistent with natural fluid diffusion and mixing, with no frame where the color pattern jumps, flickers, or reverses direction.