Why do they put phospheric acid in soda?

Question

It has no redeeming value, nutritionally speaking, so why do they put it in diet soda? Does it have some kind of addicting affect?

Answer 1

Preservative.

Answer 2

JC is right; preservative.  You're right too, it has no redeeming value and it rots your teeth.  Since you normally drink soda straight away after opening the bottle, it doesn't need preservative.  It just needs sterilising when it's bottled.