An acid is a chemical compound which when dissolved in water gives a solution with a pH less than 7. An acid HA in water reacts to give H+ or Hydronium ions which are represented as H3O+. So we have HA + H2O --> H3O+ + A- . The hydronium ion leads to the decrease in pH. An acid turns litmus paper red.
A base or an alkali on the other is a chemical which dissolves in water to increase the pH. The base reacts with water to create more OH- ions. A base like NaOH when dissolved in water undergoes the following: NaOH --> Na+ + OH-. The OH- reacts with the hydronium ion to form H2O. This increases the pH of the water. A base turns litmus paper blue.
Common examples of acids in daily life are acetic acid, citric acid, lactic acid etc. Common examples of bases or alkalis in everyday life are Ammonia, Sodium hydroxide, etc.
Acid are the substance that can donate protons like HCl, H2SO4
HCl ======> H+ + Cl-
H2SO4======> 2 H+ + SO4(2-)
Both of them give out protons (H+) so they are acid
Now Base are those substance whcih can give hydroxide ions. example : NaOH, Ca(OH)2
NaOH =====> Na+ + OH-
Ca(OH)2 =====> Ca2+ + 2 (OH)-
So both can given OH- ions so they are base