Domain: Natural Science — Chemistry
Target concept: Sodium alginate droplets form gel beads in a calcium chloride solution.

Video generation prompt: A pipette is dripping sodium alginate solution into a beaker containing a calcium chloride solution on the laboratory bench, and the solution is gently stirred as more droplets are added.

Evaluation guide:
(i) Target concept: Ion-induced polymer gelation forming spherical hydrogel microbeads.
Minimum mechanism: Sodium alginate must be in aqueous solution; calcium chloride must be in aqueous solution; droplet must make physical contact with calcium chloride solution; cross-linking must occur *at the interface* to yield a solid-like spherical shell that resists coalescence and retains shape under mild agitation.
(ii)Storyline: [Phase 1] Pipette held stationary above beaker containing clear liquid → [Phase 2] Droplet detaches and falls vertically → [Phase 3] Droplet contacts liquid surface and deforms minimally on impact → [Phase 4] Within <1 visual frame of immersion, droplet transforms into spherical, optically distinct bead with sharp boundary → [Phase 5] Bead settles slightly, remains suspended, and withstands concurrent stirring motion without deformation, merging, or dissolution. All phases unfold continuously from fixed frontal/slightly elevated lab bench viewpoint with consistent lighting and no occlusion.

Manual:
Experimental Procedure
1. Fill a clear glass beaker halfway with colorless calcium chloride solution.
2. Draw sodium alginate solution into a pipette.
3. Hold pipette vertically above beaker and gently squeeze to release discrete droplets into solution.
4. Simultaneously stir solution gently with glass rod while adding droplets.
Observation of Experimental Phenomena
Sodium alginate droplets instantly form spherical, translucent-to-milky gel beads upon contact with calcium chloride solution; beads remain discrete, do not dissolve, and suspend in solution during stirring.
Summary of Experimental Principles
Calcium ions (Ca²⁺) from calcium chloride cross-link sodium alginate polymer chains, forming instantaneous hydrogel beads via ionic gelation — a reversible physical gelation process dependent on ion concentration and polymer chain interaction.

Prompt Grounding rubric:
level_1: No pipette, no beaker, no visible sodium alginate solution, no calcium chloride solution, and no dripping or stirring action is shown at all.
level_2: A pipette, a beaker, or some liquid shows up, but not arranged the way the prompt describes: the pipette isn't held above the beaker, no droplets are released, and any stirring motion has nothing to do with the beaker's contents.
level_3: The pipette is positioned above a beaker of liquid and visibly releases sodium alginate solution as discrete droplets that fall toward the beaker; a stirring motion is visible at the liquid surface; the pipette, beaker, and stirring all appear together in one continuous shot from a fixed viewpoint, with the droplets clearly leaving the pipette tip and heading toward the liquid.
level_4: All elements of score 3 are present AND the dripping and stirring happen at the same time rather than one after the other; the pipette stays at a consistent height and angle above the beaker between drips; the stirring stays localized near the surface rather than sloshing liquid out of the beaker; the camera framing keeps the pipette tip, the beaker, and the liquid surface all in view together throughout, with nothing blocking the drip point.
level_5: All elements of score 4 are present AND every droplet's path from the pipette tip to the liquid surface is unbroken and visible, with no droplet cutting away mid-fall; the stirring tool's motion pattern stays the same style throughout (e.g., a consistent circular sweep) rather than changing technique partway; the beaker stays in the same spot and orientation on the bench from the first frame to the last; the whole sequence (positioning, dripping, and stirring) plays out with no jump cut, camera-angle change, or repositioning of any prop.

Scientific and Causal Correctness rubric:
level_1: No state change happens: every liquid stays fully fluid, no solid ever appears; the falling droplets look no different from the surrounding solution; the calcium chloride solution or the alginate solution is shown in a color that doesn't match reality (e.g., the calcium chloride solution appears blue, or the alginate looks opaque white before it ever touches the calcium chloride).
level_2: Droplets reach the liquid but merge straight into it instead of holding a shape; no droplet keeps a rounded form or a visible boundary against the surrounding solution; the stirring just blends everything together evenly rather than leaving any localized bead-like structures.
level_3: Droplets keep a rounded shape right as they touch the calcium chloride solution instead of dispersing instantly; a few of them read as separate, rounded objects sitting in the liquid, distinguishable in shade or clarity from the clear solutions around them (e.g., cloudy or milky-white against clear liquid), but they don't hold that shape once stirring starts, or their sizes and shapes vary wildly from one to the next.
level_4: Droplets turn into rounded, separate beads as soon as they reach the calcium chloride solution and keep that shape and a consistent milky or translucent look while stirring continues; none of them dissolve back into the liquid; nearly all beads look solid rather than liquid, but a bead or two briefly touches another and flattens or merges for a moment during stirring.
level_5: Every droplet that reaches the calcium chloride solution becomes a stable, rounded bead right away; all the beads keep the same milky or translucent look, clearly different from the two clear starting solutions; the beads stay separated and suspended through the stirring with no merging, dissolving, or flattening; nothing shown looks like leftover liquid trapped inside a bead.

Spatiotemporal Consistency rubric:
level_1: Severe breaks: the pipette or the beaker disappears and reappears between frames; the liquid's surface height changes abruptly with no pour or motion shown causing it; the stirring reverses direction or stutters in a way that makes no physical sense; a bead jumps to a new spot in the beaker with no path shown getting it there; the lighting or the shadows shift abruptly with no clear cause.
level_2: Several moderate problems appear together: the pipette tip moves around without ever releasing a drop; the beaker's position or angle changes partway through with no camera movement to explain it; the stirring starts or stops with no easing in or out; beads appear already fully formed before any droplet has entered the liquid; the liquid's surface doesn't show a believable reflection or ripple pattern.
level_3: One small, isolated glitch is tolerable (a brief, visible wobble in the pipette's position while it's dripping, or a bead becoming briefly hidden behind the stirring rod without popping back in a strange spot, or the surface motion looking slightly out of step with the stirring direction for a moment), but overall, which object is which, the fixed camera angle, and the drip-then-bead-forms order all stay clear.
level_4: All elements of score 3 are present AND the pipette moves steadily as it releases each drop; the beaker doesn't drift from its spot; the stirring tool sweeps in a smooth, continuous path; beads show up right where a droplet entered and stay visible through the stirring without vanishing or jumping position, though one bead might appear a beat later than its droplet actually landed.
level_5: All elements of score 4 are present AND the pipette tip stays fixed above the same spot over the beaker; each droplet falls along a consistent, visible path; the beaker and the liquid surface stay geometrically steady throughout; the stirring motion is smooth and stays confined to the liquid; every bead shows up right at the point where its droplet landed and stays visible and in the same relative spot in the beaker for the rest of the sequence.