Why does a tin can for containing food get rusty even though cans cannot rust?

This is not entirely true. Tin cans can indeed rust, although they are made of steel which is coated with a thin layer of tin to prevent corrosion. Over time, this tin layer can wear off or become damaged, exposing the steel beneath to oxygen and water, which leads to rust formation.

Here are a few reasons why tin cans may still rust:

1. Imperfect Coating: The tin coating on cans is not always completely uniform, and there may be small gaps or imperfections where the steel is exposed. These areas are more susceptible to rusting.

2. Scratches and Wear: The coating can become scratched or worn off during transportation, handling, or opening the can, exposing the steel to the environment.

3. Acidic Food Products: Some food products, such as fruits and tomatoes, have a higher acid content which can corrode the tin coating and accelerate the rusting process.

4. Dents: Dents or damage to the can can compromise the integrity of the tin coating, allowing rust to form.

5. High Humidity and Moisture: Storing cans in humid or moist environments can increase the chances of rust formation, as moisture can seep through any imperfections in the coating.

To prevent rusting, tin cans should be stored in a cool, dry place and should not be left open for extended periods of time. If you notice rust on a can, it is best to discard the contents and replace the can.