Question

How to determine strength of acid or base?

Answer 1

Acid strength is an acid's ability or tendency to lose a proton. Different acids should have different strengths. There are very few strong acids which are completely ionized in water or solution by loosing one proton. Strong acids are strong electrolytes. In other words, one mole of strong acid HA dissolves completely in water, yielding one mole of H+ ion and one mole of conjugate base A-. A strong acid does not have any non ionized acid of HA. 

According to the equation,

HA(aq) →→ H+(aq) + A-(aq)

By contrast, weak acids are partially ionized in water or solution. In other words, one mole of weak acid HA dissolves partially in water and yields one mole of H+ ions and one mole of conjugate base A-. It has some non ionized acid and conjugate base in that solution. 

Following are some of the examples for strong acids which dissolves or ionizes 100% in water.

HCl - Hydrochloric acid
HI - Hydro iodic acid
HNO3 - Nitric acid
H2SO4 - Sulfuric acid
When the different acids and bases are dissolved in water, they should yield different hydronium or hydroxyl ion (H+) concentrations. 

If an acid is strong, it dissolves completely in water or donates their proton 100% of time, to produce the higher concentration.

If the acid is weak, it dissolves partially in water or donates their proton less than 100% of time to produce the lower concentration. Strong acid have weak H-A bond so that they can lose protons more easily.

The size of atom ‘A’ determines the strength of H-A bond. The term stability of the conjugate base is also used to discuss the acid strength. Stronger acid have a larger Ka and a more negative pka than compared to the weaker acids. The stronger acids should have ka value greater than one (ka >1). The acids which have ka value of less then one (ka<1) are considered weak.Super acids are acids which are stronger than 100% sulfuric acid. Examples for super acids is fluoro antimonic acid, magic and perchloric acid.