Domain: Natural Science — Chemistry
Target concept: Determination of Tungsten Ions in Wolframite (Sulfocyanate Colorimetric Method)

Video generation prompt: Place the wolframite powder in a test tube, add hot concentrated hydrochloric acid to dissolve it, then add a few drops of stannous chloride solution, followed by potassium thiocyanate solution.

Evaluation guide:
(i) Target concept: Visual confirmation of tungsten ion presence via hot acid dissolution, tin(II) reduction, and thiocyanate complex formation.
Minimum mechanism: Wolframite [(Fe,Mn)WO4] is resistant to dilute acid and requires hot concentrated hydrochloric acid to break down and release W⁶⁺ (along with Fe³⁺/Mn²⁺ impurities) into solution; SnCl2 must be added next to reduce interfering Fe³⁺ to colorless Fe²⁺ and to partially reduce W⁶⁺ to a lower oxidation state, since W⁶⁺ alone does not form a strongly colored complex with thiocyanate; SCN⁻ is then introduced to form the characteristic orange-red tungsten-thiocyanate complex; color must emerge only after SCN⁻ addition and only in the presence of the reduced, dissolved tungsten species.
(ii)Storyline: Frame 0–2: wolframite powder placed into stationary test tube (visible granular texture, matte gray-black surface). Frame 3–5: hot concentrated hydrochloric acid added to tube; powder gradually disperses and dissolves with gentle heating (complete dissolution confirmed by absence of suspended solids). Frame 6–7: stannous chloride solution added; solution may lighten or turn pale as iron is reduced. Frame 8–9: dropper approaches tube opening; three distinct, spherical, colorless KSCN droplets detach sequentially and enter solution surface. Frame 10: orange-red color emerges within the liquid following the third droplet's full submersion and persists; no orange-red color before the KSCN step. All events occur from fixed frontal viewpoint with consistent lighting, no cuts or camera motion.

Manual:
Experimental Procedure
1. Place wolframite powder into a clean test tube.
2. Add hot concentrated hydrochloric acid, with gentle heating, to dissolve the powder completely.
3. Add a few drops of stannous chloride (SnCl2) solution to reduce interfering iron and partially reduce the tungsten.
4. Add exactly 3 drops of potassium thiocyanate solution.
Observation of Experimental Phenomena
Wolframite powder dissolves upon heating with concentrated hydrochloric acid, forming a pale solution; after adding stannous chloride and then potassium thiocyanate, the solution develops a uniform orange-red color.
Summary of Experimental Principles
Wolframite [(Fe,Mn)WO4] is chemically resistant to dilute acid and requires hot concentrated hydrochloric acid for dissolution. Tin(II) chloride reduces interfering Fe³⁺ to colorless Fe²⁺ and partially reduces W⁶⁺, allowing the reduced tungsten species to form an orange-red complex with thiocyanate ions (SCN⁻) — the basis of the sulfocyanate colorimetric method for tungsten detection.

Prompt Grounding rubric:
level_1: No wolframite powder is shown; or no test tube is shown; or no acid addition is shown; or no potassium thiocyanate addition is shown; none of the required objects or actions appear.
level_2: At least one object (powder, tube, or a dropper) appears, but not in correct functional context (e.g., powder shown alone without a container, or a dropper held with nothing dispensed); none of the four core actions (placing the powder, adding the hot acid, adding stannous chloride, adding potassium thiocyanate) is shown.
level_3: Wolframite powder is placed inside the test tube; a concentrated acid is added to dissolve it (with some indication of heating, such as steam or a heat source); stannous chloride solution is added; potassium thiocyanate is added via dropper as three distinct droplets; the four actions occur in this order, but at least one object is unclear (e.g., no bottle label distinguishes the acid from the SnCl2 solution) or the fixed viewpoint is broken partway through.
level_4: Everything at level 3 still holds, and beyond that every object is clearly identifiable and distinct: the gray-black wolframite powder, the test tube, the acid used for dissolution (shown with heating), the stannous chloride solution, and the potassium thiocyanate solution (in a labeled dropper bottle); all four actions happen in the same test tube from the same fixed viewpoint with no missing step or object substitution, but one small flaw remains, such as a brief occlusion of a dropper tip or a minor shadow flicker.
level_5: Everything at level 4 still holds, and beyond that the powder is shown fully dissolving under heating before the stannous chloride is added; exactly three KSCN droplets are dispensed sequentially and each fully enters the liquid surface without splashing outside the tube; every object keeps the same labeling, shape, and spatial position across the entire sequence with no viewpoint shift, occlusion, or lighting discontinuity.

Scientific and Causal Correctness rubric:
level_1: No color change happens at any point; or the solid stays visibly unchanged after acid and heating are applied; or the final liquid is blue, green, or deep red rather than orange-red; or a color change happens before the thiocyanate step.
level_2: The powder partly breaks down but no clear solution forms even with heating; or a solution forms but stays gray-black or strongly colored before the thiocyanate step; or the thiocyanate step produces no color change; or the resulting color is inconsistent with a tungsten-thiocyanate complex (e.g., pure blue, green, or black).
level_3: The wolframite powder fully dissolves under the hot acid, forming a pale, largely clear solution; after the stannous chloride step the solution stays pale or lightens further; once the potassium thiocyanate is added, the solution develops an orange-to-orange-red color; the color may appear gradually or unevenly, or fade soon after appearing, but the overall color family (orange-red, not pure red or another hue) is correct.
level_4: Everything at level 3 still holds, and beyond that the solution is essentially free of undissolved solid after the acid/heating step; the orange-red color, once it appears after the third KSCN droplet, spreads through the whole liquid volume and holds steady for at least 2 seconds without fading or turning a different hue; no color appears before the KSCN step.
level_5: Everything at level 4 still holds, and beyond that no solid granules remain visible after the acid step; the pale solution stays visibly lighter after the stannous chloride addition, consistent with the reduction of iron and tungsten species; as soon as the third KSCN droplet fully contacts the solution, the orange-red color spreads evenly through the entire liquid column and holds that hue and intensity for the rest of the visible sequence, with no streaking, fading, or layering.

Spatiotemporal Consistency rubric:
level_1: The test tube appears or disappears between frames; the powder appears inside the tube with no placement motion; the liquid appears with no pouring motion; KSCN droplets appear already formed in mid-air with no dropper visible; the lighting jumps abruptly; the background behind the setup suddenly changes color or texture; the tube's shape breaks then reforms.
level_2: At least two clear continuity breaks occur: for example, the powder is placed and the very next frame shows a fully dissolved, colorless solution with no visible acid addition; or KSCN droplets appear before the dropper enters the frame; or the tube rotates more than about 45 degrees with no visible turning motion; or the shadow the tube casts switches side between two consecutive frames.
level_3: The test tube, dropper, and any heat source stay in consistent positions and orientation throughout; motion is continuous (the dropper moves smoothly toward the tube, liquid flows without jumping); the lighting and the shadow's direction stay the same throughout, aside from one minor slip, such as a brief occlusion of the dropper tip lasting well under a second, or a slight, momentary dimming of the background unrelated to the reaction.
level_4: Everything at level 3 still holds, and beyond that there is no moment where the tube, dropper, or liquid appears/disappears, breaks apart, or where the lighting jumps; every object's motion is smooth and physically plausible; the dropper always stays above the tube opening, the powder or liquid always stays inside the tube, and the liquid surface stays level; only one very minor imperfection remains, such as a faint wobble in a hand-held dropper.
level_5: Everything at level 4 still holds, and beyond that the tube stays fixed at the center of the frame throughout; the powder enters the tube in one continuous downward motion; the acid is added as an unbroken stream or as clearly continuous drops; the three KSCN droplets detach individually, fall in a visible vertical path, and merge cleanly with the liquid surface, with no gap, jump, or distortion in any of these motions from first frame to last.