====== Rust removal ======

===== Ketchup =====

Ketchup contains mostly tomatoes which naturally contain oxylic acid.
The ferric oxide (rust) formed on metal surfaces is basic in nature. The acids in Ketchup neutralise the basic oxide.

===== Table salt and white vinegar =====

Table salt and white vinegar make a decent rust remover. That's because the molecules rearrange in solution to hydrochloric acid and sodium acetate.
Ferric oxide (rust) is soluble in weak hydrochloric acid solutions.

===== Table salt =====
Salt alone, or in a paste in water works to remove rust as a simple mild abrasive, but only on a mechanical level.