What chemical similarity is shared by all acids?

Acids share a number of similar chemical properties.

Some of these properties are:

1 - All acidic solutions have a pH value less than 7

2 - Acids react with metal carbonates producing a salt, carbon dioxide and water

3 - Acids react with bases producing salt and water (This reaction is known as neutralization reaction)

4 - Acids react with reactive metals producing salt and hydrogen gas