Discussion

As approximately 100ml (an excess) of 1M potassium iodide KI is added to the beaker in several steps, the solution reverts to clear. The addition of excess iodide to the solution results in the formation of a mercury(II) tetraiodide complex, which is soluble in water.

HgI₂(s) + 2 I^-(aq) → [HgI₄]^2-(aq)

Viewing note

There are several cuts of a few seconds each from the movie to eliminate some redundancy.