pKa Definition in Chemistry

In this up growing world, science is the one who is taking the civilization to the peak of the headway. And while classifying its different routes a very important potion of always appears. And that is called chemistry. In the field of chemistry experimental works with acids and bases is now a common story. And while working with various acids and bases in a regular basis one must know about two similar values called pH and pKa regarding to it. so if you are the one who is getting trouble to know the entire information about pH and pKa then here is the solution given below.

Definition of pKa

There before I have already mentioned about the pH of an acid in an article. So the pH of an acid defines the rate of acidity of that particular acid or how strong that acid is. So as comparing to pH, pKa also defines the strength of an acid solution depending on its dissociation rate. So now coming to the actual point that what is pKa? pKa is the negative value of base-10 logarithm of the acid dissociation constant of a solution which is identified as (Ka). So basic formula to brings the value of pKa is as follows

                                                          pKa= -log10ka

How much the value of the pKa will decrease that much the strength of the acid will increase. For example I hope we all know that the pKa of formic acid is 3.75 and the pKa of lactic acid is 3.8. So depending on the different values of pKa it becomes very easy to identify that which is strong acid among this two.

Why the term pKa is used instead of Ka?

The main reason behind using the term pKa over Ka is because the value of pKa can describe the rate of dissociation of an acid in very small numbers in decimal. And it is not that the same thing cannot be described by dissociation constant Ka but very often it is not used because the value that will come from it will be very small and will keep some scientific notation along with it. so normally it becomes bit difficult for the people to go deeper about the fact.

Important points about pKa

  • From the given information it is clearly visible that pKa is nothing but the method of knowing the strength of a specific acid by its dissociation rate.
  • pKa is the negative log value of the dissociation constant (Ka) of the acid.
  • The lower value of pKa reveals the fact that the particular acid is a strong acid and it completely dissociates in water. And the higher value indicates that the particular acid is a weak acid and it partially dissociates in water.

Brief explanation of pKa

Acid dissociation constant (Ka) also known as the acid ionization constant is a qualitative measurement for examines the straightness of an acid solution. It is also called as the equilibrium constant of a specific chemical reaction which is most probably used in the acid-base reactions. For example if we take a chemical component that holds a chemical formula of HX. And when it dissociates in water it breaks into two parts, first one is the H+ ion and the second one is Xion which is the conjugate base of the acid. The whole system of the solution will reach the position of equilibrium when the concentration of its components remains same with the respect of changing time. Only then the forward reaction and reverse reaction will be happening in the same rate and same time. The basic equation that briefs the dissociation constant is

                                                   Ka= [H+] [X]/ [HX]

                                    Or pKa= -log10Ka = [HX]/ [H+] [X]

Strong acids

The ionization rate of the acid in the solution is completely depends on the polarity or the distribution of the electrons in a chemical bond. When two atoms in a bond have nearly same electro negativity values, the electrons in the bond are fifty-fifty shared and spend equal time regarding their atoms. And in the other hand when it is shown that there is a significant difference of electro negativity values in the atoms there occurs a separation of charge and as a result electrons present in a bond is mostly taken by a certain atom than the other atom.

Hydrogen atoms gather slightly positive charge when it gets bonded to an electro negative element. If there is less electron density regarding to a hydrogen atom then it becomes easier to get ionized and the molecule becomes more acidic. Weak acids basically take the formation when there is less polarity presented between the hydrogen atom and the other atom and that doesn’t allow the easy removal of the hydrogen ion.

Another factor that affects the strength of an acid is the size of the atom according to the size of the hydrogen atom. If the size of the atom increases then the strength of the bond decreases so that it becomes really easy to break the bond and release the hydrogen ion and increases the strength of the particular acid

Explanation by experimental application

The experimental application of pKa comes from the process of titration that is commonly being used in the chemistry labs. In this procedure a specific component is being acidified with the presence of a strong acid in a medium which have a high ionic strength at a certain temperature. In this entire procedure firstly the acidified solution gets completely protonated. Then the solution is taken for being titrated with a strong base until all the protons get removed from the acidic solution. At each and every point of the titration the pH of the solution is measured with the help of a pH meter. So that the equilibrium constants of the solution could be found.

It is quite appropriate that the volume of the added base will be much lesser than the total volume of the acid solution that was being titrand. This fact gives the assurance that the value of pKa will always remain same.

Final words

So here I have given some important facts about the values of dissociation constant (Ka) and pKa. So if you are the one trying to know about the amazing equation that represents the strength of an acid then this should be your way to go. Read out all the information given above carefully. I hope it will really help you out.

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