Acids are ionic compounds (a compound with a positive or negative charge) that break apart in water to form hydrogen ion (H+). Characteristics of acid: Acid taste sour. Acids also react strongly to metals, generally with the evolution of hydrogen gas (Eg: Zn + HCI). Also strong acids are dangerous and can burn your skin off. Acids change litmus red. Acids become less acidic when mixed with bases. An acid has Ph scale of under 7.