There are actual several definitions of acids and bases. The simplest of these is the Arrhenius definion. An acid is a substance, such as HCl, that generates H+ ions in water. A base (also known as an alkali), such as NaOH, is a substance that generates OH- ions in water. Another common acid-base definition is Bronsted-Lowry which states that an acid is a proton donor and a base is a proton acceptor. The Bronsted-Lowry definition is broader and more accurately represents acids and bases. It also accounts for the fact that some substances, such as water can act as an acid or a base depending on what the other reactant is. H2O can donate a proton when paired with a base such as NH3 and accept a proton when paired with an acid such as HCl.
An acid is a compound which on ionisation in water gives hydronium ions as the only positively charged ions.
An alkali is a water soluble base. It always furnishes OH- ions.
A base is a compound which on ionisation gives OH- as the only negatively charged ions.
Acids are the substances which give hydrogen ions when dissolved in water.They are sour in taste and turn blue litmus into red. they dont have any effect on red litmus paper. They are sour in taste.
Bases are the substances which gives hydroxide ions when dissolved in water. They are bitter in taste. They turn red litmus to blue. they dont have any effect on blue litmus.
bases which are solouble in water are called alkalis..