1. acid reacts with metal to give metal salt and hydrogen...(hydrogen can be detected by burning matchstick near that gas producing POP sound) e.g.
2HCl + 2Zn-------> 2ZnCl + h2
2. acid dissociate in water to form hydronium ion which turn ph indicator's color red or warm colour (i.e. red orange yellow etc) depending upon how strong your acid is.
3. acid react with metal carbonates and metal bicarbonates to form salt water and carbon dioxide. e.g.
CH3COOH + Na2CO3 -------> CH3COONa + CO2 + H2O
4.they turn blue litmus red.
5. they react with base to form salt and water (neutralization reaction)e.g.
NaOH + HCl -------> NaCl + H2O