Unlike precipitation reactions, those involving acids may or may not have characteristic visual cues. Of the four types of acid reactions you saw in the lab, only two had distinctive physical changes:

• acids react with metal carbonates to release carbon dioxide gas (bubbles)
• acids react with many metals to release hydrogen gas (more bubbles)

Of these two, the second is actually a redox reaction. So what is going on in many acid reactions if we can't see much?

All acids are electrolytes. You can generally tell a substance is an acid from its formula. Most acid formulas begin with H. All acid names end with "acid" (duh...). The nomenclature of acids can be complicated and since we only deal with a few during the year, it is easier to simply learn those few.