Domain: Natural Science — Chemistry
Target concept: Electrolysis of Copper Chloride Solution

Video generation prompt: Insert the graphite electrode into a copper chloride solution, connecting the anode to the positive terminal of the power supply and the cathode to the negative terminal. After applying electricity, observe the changes occurring at both electrodes.

Evaluation guide:
(i) Target concept: Electrolytic reduction of Cu²⁺ at the cathode and oxidative discharge of Cl⁻ at the anode in aqueous CuCl₂ using inert graphite electrodes, producing a copper deposit and visible chlorine gas bubbling at the same time.
Minimum mechanism: Graphite must remain chemically inert; the solution must be aqueous CuCl₂ (pale green from hydrated Cu²⁺); the applied DC current must drive Cu²⁺ toward the cathode and Cl⁻ toward the anode; Cu²⁺ reduction to solid copper is favored at the cathode; Cl⁻ is discharged at the graphite anode ahead of water (lower overvoltage), producing visible chlorine gas bubbles at the anode along with a fading green tint as Cu²⁺ becomes locally depleted there.
(ii)Storyline: [Phase 1: Setup] Two graphite rods inserted vertically into pale green CuCl₂ solution in a fixed-view beaker; [Phase 2: Connection] Rods wired to clearly marked +/− terminals — red wire to one rod, black to the other; [Phase 3: Activation] Power-supply switch flips or an indicator LED lights up synchronously with the onset of the phenomena; [Phase 4: Cathode Response] A red-brown metallic copper deposit appears and grows continuously on the negative-connected rod; [Phase 5: Anode Response] Gas bubbles form and rise from the positive-connected rod while the green hue visibly fades in that vicinity; [Visibility constraint] All phenomena occur within the same fixed frame; the electrode–solution interface stays fully in view; no occlusion by hands or tools during the observation phase.

Manual:
Experimental Procedure
1. Insert two identical graphite rods into a transparent container filled with copper chloride solution.
2. Connect one rod to the positive terminal (anode), the other to the negative terminal (cathode) of a DC power supply.
3. Turn on the power supply.
Observation of Experimental Phenomena
- Red-brown solid deposits exclusively on the cathode (negative-connected rod).
- Green color of the solution fades locally around the anode (positive-connected rod).
- Gas bubbles form at the anode (positive-connected rod) only; no gas forms at the cathode.
Summary of Experimental Principles
Copper ions (Cu²⁺) gain electrons at the cathode and deposit as solid copper metal. Chloride ions (Cl⁻) are discharged at the graphite anode ahead of water, losing electrons to form chlorine gas (Cl₂), which appears as visible gas bubbles at the anode; this loss of Cl⁻, together with Cu²⁺ migrating away from the anode toward the cathode, causes the green color to fade locally near the anode.

Prompt Grounding rubric:
level_1: No graphite electrodes are visible; no container of copper chloride solution appears; no power-supply terminals are shown; no insertion or wiring action is depicted; the scene bears no resemblance to an electrolysis setup.
level_2: A graphite electrode and a liquid-filled container both appear, but the electrode is not inserted into the liquid; power-supply terminals are missing or left unconnected; there is no clear labeling or color-coding tying either electrode to a terminal polarity.
level_3: Two graphite electrodes are inserted into a transparent container of solution; two distinct terminals (labeled or color-coded, e.g., red/black) are visible; one electrode is wired to the positive terminal and the other to the negative terminal; the insertion and wiring actions are shown in sequence.
level_4: All elements from score 3 are present AND both electrodes remain fully submerged and stationary once wired; each wire runs to its corresponding electrode without crossing or ambiguous connections; the container shape (e.g., beaker) stays consistent across frames; nothing occludes the electrode–solution interface.
level_5: All elements from score 4 are present AND both electrodes are identical, matte black/grey cylindrical graphite rods with no metallic sheen; the container holds only clear-to-pale-green liquid with no bubbles or precipitate before current is applied; the wiring is taut and unbroken; the '+'/'−' or red/black polarity markings are legible and correctly assigned; the camera stays fixed on the electrode–solution interface throughout.

Scientific and Causal Correctness rubric:
level_1: No observable change occurs at either graphite electrode after current is applied; or the observed changes contradict the electrochemistry of CuCl₂ electrolysis (e.g., gas bubbles form at the cathode instead of the anode, the green color fades at the cathode instead of the anode, or a red-brown copper deposit forms at the anode instead of the cathode).
level_2: Only one of the two expected electrode phenomena appears, or phenomena are assigned to the wrong electrode: e.g., the copper deposit correctly forms on the cathode but no gas bubbling appears at the anode, or gas bubbles form at the cathode instead of the anode, or the same phenomenon (bubbling or deposit) appears identically at both electrodes.
level_3: A red-brown copper deposit appears exclusively on the cathode (negative-connected rod); the green color of the CuCl₂ solution visibly fades in the region around the anode (positive-connected rod); gas bubbles are visible rising from the anode surface only, with no bubbling at the cathode.
level_4: All elements from score 3 are present AND the copper deposit forms as a continuous adherent layer on the cathode surface (not loose floating particles or sediment); the anode gas bubbles form directly at the graphite surface and rise through the solution; the solution's decolorization is localized to the anode region and spreads outward gradually; no copper deposit forms at the anode and no gas bubbling occurs at the cathode.
level_5: All elements from score 4 are present AND the cathode deposit is uniformly red-brown with a metallic luster (not dull grey or black); the anode shows both clear localized fading of the green hue and steady, uninterrupted gas bubble evolution; the onset of copper deposition and anode gas bubbling begin together, synchronized with the moment current is applied, with no delay or premature appearance of either phenomenon.

Spatiotemporal Consistency rubric:
level_1: The electrodes or their wiring appear to jump between positions from one frame to the next; the beaker vanishes and reappears; the liquid level changes abruptly without a pouring or evaporation cause; an electrode's tilt or depth changes with no visible motion causing it; the scene's illumination or shadow pattern jumps abruptly between frames.
level_2: One clear break in continuity occurs: an electrode appears already submerged with no insertion motion shown; the solution's color changes instantly rather than fading gradually; the wiring looks fully connected in one frame and disconnected in the next; the camera view rotates or zooms without a smooth transition.
level_3: The two electrodes stay at a fixed distance from each other and from the container walls; the liquid surface stays level and does not shift unexpectedly; nothing on screen flickers, warps, or breaks apart; the direction and brightness of the light source do not change; any hand motion used to insert an electrode or connect a wire moves at a steady, continuous pace.
level_4: All elements from score 3 are present AND each electrode's depth of immersion stays constant once inserted; the electrodes and container rim keep the same relative screen position as the camera holds still; the electrode tips stay aligned with the liquid surface without drifting; brightness and contrast around the electrodes stay even so the copper deposit and bubble formation remain clearly visible.
level_5: All elements from score 4 are present AND the sequence of insertion, wiring, current application, cathode copper deposition, and anode bubbling/decolorization plays out in that order with no phase skipped or shown out of sequence; no frame is repeated, frozen, or played in reverse; every motion (hand, bubbles, growing deposit) proceeds continuously in one direction without stalling or reversing.