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Question: A certain weak acid has\({K_a} = 1.0X{10^{ - 4}}\). Calculate the equilibrium constant for its react...

A certain weak acid hasKa=1.0X10−4{K_a} = 1.0X{10^{ - 4}}. Calculate the equilibrium constant for its reaction with a strong base.

Explanation

Solution

Dissociation constant here for the acid is the measure of the dissociation ability of that particular solution. Dissociation means the breakdown of any substance. When any acid meets a certain type of solution, it breaks down to release protons or H+{H^ + }ions. These are used to measure the acidity of any solution. The more the protons, the more acidic the solution becomes. We can also call it the strength of this acid in the solution.

Complete step-by-step answer:
The dissociation constant for acid is also called acidity. For example if we take the chemical species HAHA which is an acid and it dissociates into A−{A^ - }, which is a conjugate base of the acid and a hydrogen ion, H+{H^ + }, then if the system is in equilibrium, then there will not be any changes in the concentration of the components.
To find out the dissociation constant we use the following equation:
HA⇌H++A−HA \rightleftharpoons {H^ + } + {A^ - }
{K_a} = [{A^ - }][{H^ + }]/[HA] \\\ \\\
or
pKa=log⁡10Ka=log⁡10[HA]/[A−][H+]p{K_a} = {\log _{10}}{K_a} = {\log _{10}}[HA]/[{A^ - }][{H^ + }]
Thus here the ionic product, Ka=[H+][A−]/[HA]{K_a} = [{H^ + }][{A^ - }]/[HA] =10−4......(i) = {10^{ - 4}}......(i)

The reaction with strong base can be expressed as:
HA+OH−⇌H2O+A−HA + O{H^ - } \rightleftharpoons {H_2}O + {A^ - }
K=[A−][H2O]/[OH−][HA].........(ii)K = [{A^ - }][{H_2}O]/[O{H^ - }][HA].........(ii)
Also, Ka=[H+][OH−]=10−14...........(iii){K_a} = [{H^ + }][O{H^ - }] = {10^{ - 14}}...........(iii)
So, from equations (i),(ii)and(iii),(i),(ii)and(iii),
K=Ka/Kw=10−4/10−14=1X1010K = {K_a}/{K_w} = {10^{ - 4}}/{10^{ - 14}} = 1X{10^{10}}

Note: The dissociation concept is used in various areas such as chemistry and pharmacology. The affinity between a protein and ligand is defined by the protein-ligand binding the dissociation constant. The less the dissociation constant, the more tightly the bond of ligand is present. When we talk about the antibody-antigen binding, the concept used here is called the inverted dissociation constant and it is defined by the constant called as affinity constant.