Imagitive uses of Fabricate.

[TheApapalypse]

A Merman is attacking.

The sodium being taken in by his gills with the sea water becomes Lye.
----one cubic foot---- in, through, around, out, and as much as it takes to become a cubic foot of LYE.

If one argues you must target the seaWATER ....Salt content:

'A cubic foot of seawater contains about 2.2 pounds of salt' according to San Diego State University."

If it is water that is targeted it becomes ten cubic feet and then 22 POUNDS of salt---

Definitely going to be some fort and concentration checks...acid damage as well?

[Mysterious Stranger]

First, the character needs to have an appropriate craft skill to make an item with Fabricate. Since Electrolyzing water is a modern technique, the character will not have the relevant craft skill.

Second quality of the finished item depends on the quality of the base material. Ocean water is probably considered very low quality for making lye. Before electrolyzing sea water, it is filtered and treated. Typically, you also add electrolytes and potassium hydroxide. This will mean the quality of the lye created is extremely poor.

Finally, the casting time of the fabricate is measured in full rounds. That will give the merman a time to move out of the area you are creating the lye in. Since you are underwater, the lye will also end up being diluted. Given the slow creation time and poor quality of the lye it probably will not do that much.

Salt (Sodium) is considered a mineral so the target is reduced to 1 cubic foot per level.

[Oli Ironbar]

Doesn't necessarily sound like electrolysis depending on the spell. Does fabricate specify it stays the same material?

How many ranks in alchemy gets you how far on the periodic table? Unlike seventeenth century versions, PF alchemy does work in many instances.

[Mysterious Stranger]

Who is to say that the laws of physics in a world where magic works is the same as our world. As Oil Ironbar brought up Alchemy in the Pathfinder universe actually works. If medieval alchemy actually works that would seem to indicate that the natural laws of the universes diverge at some point. That being the case electrolysis may not work.

[Java Man]

This is the same logic I can use kill everyone in a room by making NOx from the atmosphere. Or you can use the spell as intended instead of trying to cheese it into a deathspell, really up to you and your GM.