Question

Among the following, the dissociation constant is highest for:
A: ${C_6}{H_5}OH$
B: $C{H_3}OH$
C: $C{H_3}C \equiv CH$
D: $C{H_3}N{H_3}^ + C{l^ - }$

Answer 1

Hint : Atoms can either gain or lose electrons to form ions in a phenomenon known as ionization and compounds that are formed in this manner are known as ionic compounds). When these ionic compounds are dissolved in water, they yield ions in a process known as dissociation.

Complete Step By Step Answer:
If the compound has an ability to lose a proton easily in water (i.e. hydrogen can be easily removed), then that compound will possess a low dissociation constant. Now, let us look at the different compounds given in the options one by one:
Option A: ${C_6}{H_5}OH$

As clear from the figure, H atom of hydroxyl group will create hydrogen bonds with water molecules and thus in ${C_6}{H_5}OH$ hydrogen can be easily removed. Hence, dissociation constant will be low in this case.
Option B: $C{H_3}OH$

As clear from the figure, H atom of hydroxyl group will create hydrogen bonds with water molecules and thus in $C{H_3}OH$ hydrogen can be easily removed. Hence, dissociation constant will be low in this case.
Option C: $C{H_3}C \equiv CH$
As we know, alkyne possesses acidic hydrogen which can easily be removed as shown in figure. Hence, dissociation constant will be low in this case.

Option D: $C{H_3}N{H_3}^ + C{l^ - }$

As clear from the above figure, nitrogen and chlorine induces the inductive effect ( $- I$ ) and attracts hydrogen towards themselves due to which hydrogen cannot be removed easily. Hence, in this case the dissociation constant will be very high.
As a result, the correct answer is Option D.

Note :
For a generalised chemical reaction taking place in a solution:
$aA + bB \rightleftharpoons cC + dD\;$
The equilibrium constant can be expressed as follows:
$K = \dfrac{{{{[C]}^c}{{[D]}^d}}}{{{{[A]}^a}{{[B]}^b}}}$
where [A], [B], [C] and [D] refer to the molar concentration of species A, B, C, D respectively at equilibrium. The coefficients like a, b, c, and d in the generalised chemical equation become exponents as seen in the above expression. ${K_a}$ is acid dissociation constant and ${K_b}$ is base dissociation constant.