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Q. Define acid and base?
Ans: According to Arrhenius any compounds that contain hydrogen and can dissolve in water to release hydrogen ions into solution is called acid. For example, hydrochloric acid (HCl) dissolves in water as follows:
HCl +H2O→ H+ (aq) + Cl-(aq)
According to Arrhenius any compounds that dissolve in water to release hydroxide ions (OH-) into solution is called base. For example, sodium hydroxide (NaOH) is a base dissolves in water as follows:
NaOH + H2O→ Na+(aq) + OH-(aq)
According to The Brønsted-Lowry definition acid is any substance that can donate a hydrogen ion . (Under the Brønsted definition, acids are often referred to as proton donors because an H+ ion, hydrogen minus its electron, is simply a proton).
According to The Brønsted-Lowry definition bases is any substance that can accept a hydrogen ion. NaOH and KOH, are bases because they can accept an H+ from an acid to form water.
However, the Brønsted-Lowry definition also explains why substances that do not contain OH- can act like bases. Baking soda (NaHCO3), for example, acts like a base by accepting a hydrogen ion from an acid as illustrated below:
HCl + NaHCO3 → H2CO3 + NaCl
In this example, the carbonic acid formed (H2CO3) undergoes rapid decomposition to water and gaseous carbon dioxide, and so the solution bubbles as CO2 gas is released