Difference Between Strong and Weak Acids and Bases

Strong vs Weak Acids vs Bases
 

Acids are defined in several ways by various scientists. Arrhenius defines an acid as a substance that donates H₃O⁺ ions in the solution, whereas base is a substance that donates OH^– ions to the solution. Bronsted- Lowry defines an acid as a substance that can donate a proton and a base as a substance that can accept a proton. Lewis acid definition is far common than the above two. According to it, any electron pair acceptor is an acid and a donator is a base. According to the Arrhenius definition, a compound should have a hydroxide anion and the ability to donate it as a hydroxide ion to be a base. According to Lewis and Bronsted- Lowry, there can be molecules, which don’t possess hydroxides, but can act as a base. For example, NH₃ is a Lewis base, because it can donate the electron pair on nitrogen. Na₂CO₃ is a Bronsted- Lowry base without hydroxide groups, but has the ability to accept hydrogens.

Strong and Weak Acids

Regardless of the above definitions, we normally identify an acid as a proton donor. Acids have a sour taste. Lime juice and vinegar are two acids we come across at our homes.  They react with bases producing water and react with metals forming H₂, thus increase metal corrosion rate. Acids can be categorized into two, based on their ability to dissociate and produce protons. Strong acids like HCl, HNO₃ are completely ionized in a solution, to give protons. Weak acids like CH₃COOH are partially dissociates and give fewer amounts of protons.

K_a is the acid dissociation constant. It gives an indication of the ability to lose a proton of a weak acid. To check whether a substance is an acid or not we can use several indicators like litmus paper or pH paper. In the pH scale, from 1-6 acids are represented. An acid with pH 1 is said to be very strong, and as the pH value increases, acidity is decreased. 

Strong and Weak Bases

Bases have a slippery soap like feeling and a bitter taste. They react easily with acids producing water and salt molecules. Caustic soda, ammonia, and baking soda are some of the common bases we come across very often. Bases can be categorized into two, based on their ability to dissociate and produce hydroxide ions. Strong bases like NaOH and KOH are completely ionized in a solution, to give ions. Weak bases like NH₃ are partially dissociated and give fewer amounts of hydroxide ions.

K_b is the base dissociation constant. It gives an indication of the ability to lose hydroxide ions of a weak base. Acids with a higher pK_a value (more than 13) are weak acids, but their conjugate bases are considered as strong bases. To check whether a substance is a base or not we can use several indicators like litmus paper or pH paper. Bases show a pH value higher than 7, and it turns red litmus to blue.