Phosphoric acid
It is used to make sodas sour. It is also used when a nonreactive acid is needed. It can be used to make hydrogen halides, such as hydrogen chloride. Phosphoric acid is heated with a sodium halide to make the hydrogen halide and sodium phosphate. It is used to react with rust to make black iron(III) phosphate, which can be scraped off, leaving pure iron. It can be used to clean teeth.