Correct statements about the percentage ionization of weak acids in water include which of the following?
I The percentage ionization increases as the ionization constant of the acid becomes larger.
II The percentage ionization increases as the concentration of the acid becomes smaller.
Both I and II
Neither I nor II
The ionization of a weak acid, HA in water, can be represented as:
`HA stackrel larr rarr H^(+) (aq.) + A^(-) (aq.)`
It follows from the expression that, at a given experimental condition, larger the value of `K_a` , greater is the concentration of free ions in solution, hence greater is the extent of ionization.
Therefore, statement I is correct.
Again, applying degree of dissociation concept to the dissociation equilibrium:
`HA stackrel larr rarr H^(+)(aq.) + A^(-)(aq.)`
`c(1-alpha)` `alpha*c` ` alpha*c`
=`alpha^2c` (`alpha` is very small, so `(1-alpha)~~1` ` ` )
alpha, the degree of dissociation increases when c, the molar concentration decreases. So, statement II is also correct.
Hence, correct answer is C).