Which acid to choose when designing a world with acid seas?
Coca Cola or a mixture of Coca Cola and Pepsi Cola would probably be a good choice.

It's not immediately fatal for carbon life forms that fall into it. Only prolonged exposure will cause digestion and damage to bones and teeth.

Due to the phosphoric acid ships with iron hulls would withstand corrosion due to passivation through the formation of iron phosphate (also a molluscicide to protect from shipworms).

In agriculture phosphate is also a potent fertilizer.

For propulsion purposes, Cola together with Mentos is a well-known hybrid rocket propellant.