Question

What do you understand by the strength of an acid? On what factors does the strength of an acid depend?

Answer 1

The strength of an acid refers to its ability or tendency to lose a proton or its degree of ionisation. A strong acid ionises completely in an aqueous solution, giving rise to maximum concentration of hydronium ions, e.g., HCl, ${\mathrm{H}}_2{\mathrm{SO}}_4\mathrm{and}{\mathrm{HNO}}_3$. A weak acid ionises partially or incompletely in an aqueous solution, giving rise to lesser concentration of hydronium ions along with molecules of the acid, e.g., ${\mathrm{CH}}_3\mathrm{COOH},(\mathrm{COOH}{)}_2\mathrm{and}\mathrm{HCOOH}$.

Following are the factors on which the strength of an acid depends:
1. The bond that attaches the acidic proton to the remaining molecules decides the acidity of the substance. The weaker the bond, the stronger will be the acid.
2. If the electrons are evenly shared between the proton and the neighbouring atom, then the bond is said to be non-polar. If the electrons are not shared evenly, then the bond is polar. The greater the polarity of the bond, the stronger will be the acid.