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What Is The Difference Between pH And pKa? (Difference Cleared)

What Is The Difference Between pH And pKa? (Difference Cleared)

A branch of chemistry that deals with and manages matter’s performance at both atomic and molecular levels. It also involves the study of how chemical reactions take place. The branch includes physics to recognize chemical structures and reactions.

The terms pKa and pH in physical chemistry both refer to the acidity of a system. The key distinction between pKa and pH is that the former indicates acid dissociation, while the latter indicates the acidity or alkalinity of a system.

Physical chemistry is essential in studying other branches of chemistry and providing basic knowledge of thermodynamics that perform chemical reactions ahead. In this branch of chemistry, we study both the physical and chemical properties or resources of the substance at the same time.

What is the System’s Acidity?

pH and pKa are referred to the physical chemistry
pH and pKa are referred to the physical chemistry.

Every substance consists of acid or base. If the system’s hydrogen ion concentration is high, it refers to acidic. In comparison, a system with low hydrogen concentration refers to a basic or alkaline solution.

We determine the acidity of any solution by using a scale called the ph scale. All the solutions with a ph less than seven are acidic, and those with a ph greater than seven are known to be bases.

In this article, we learn about how pH and pKa are different from each other. Without any delay, let’s get started.


Simply, pH evaluates the hydrogen ion concentration in any liquid or solution. It ranges from 0 and ends at 14.

If any solution with pH 7 indicates, the solution is naturally neutral. pH also measures the amount of hydrogen and hydroxyl ions in the solution.

If the solution is rich in free hydrogen ions is known to be acidic. In contrast, the solution with the relative amount of hydroxyl ions indicates the essential nature of the liquid. 

Solutions or compounds with a pH less than seven at 25 C are acidic, and solutions with a pH greater than seven at 25 C are considered basic.

How Does the pH of the Solution Measured?

Pure distilled water separates equal amounts of hydrogen and hydroxyl ions:

H2O ↔ H+ + OH-

pH is a logarithmic unit, the equation that represents how to calculate the pH of any solution is:

pH = -log[H+]

H+ refers to hydrogen movement that might be different depending on the concentration.

The above equation was suggested by Danish biochemist Soren Peter Lauritz Sorensen in 1909. The name pH is derived from the German word potent means power after combining with H. Hence, pH is the symbol for the power of hydrogen.

On the other hand, pH is the negative logarithm of the hydrogen ion present in the liquid. Usually, it is measured by rinsing a glass electrode into the aqueous solution.

Measuring pH of a solution
Measuring the pH of a solution

1. Measuring pH by the Electrical Method

This method is very popular for measuring ph. In this method, the pH value depends on the solution’s number of electrode potentials. At the given temperature, the electrode potential is based upon the concentration of electrolyte, which is already present in the solution. 


CapE=E_°+0.0001982(273+t)/n log_10⁡a

Eo is the electrode potential

t = temperature is given to the electrode

n = valency of the system

a = is the active concentration of the ion

2. Measuring pH by the Colorimetric Method

The method is based on assumptions; in this method, the indicator shows the same color in two solutions and represents the same pH value. But, this assumption is only sometimes accurate.

The color change depends not only on the pH level but also on other factors.

3. Other Methods of Measuring pH

  • Through pH paper
  • Through pH meter
  • By using a thermos compensator
  • By differential input pH amplifier

In our daily life, we use so many different acids and bases. Some liquids except water as the examples of pH values in chemicals are as follows.

ChemicalspH value
Lemon juice12.4
Sodium hydro oxide14.0
Hydrochloric acid0.0
Soft drinks3.0
Different Chemicals and Their pH

Litmus Paper Test

Remember that solution with water has pH; if there is no water in any solution, there is no pH. For instance, vegetable oil, petrol, alcohol, and gasoline have no pH.

By using litmus paper, we can measure the pH of any solution. Litmus paper is a good indicator to tell any solutions by changing color.

The litmus paper
The litmus paper

Effect of Temperature on pH Value

Temperature effect notably impacts pH measurement. If the temperature increases, water dissociation increases. If we raise the temperature, the vibration of water molecules increases. It helps water to form more hydrogen ions. Thus, the pH of water decreases.

When it comes to pure water, the pH decreases with an increase in temperature. Due to the equal concentration of hydrogen and hydroxyl ions, the water is neutral.

Why is pH Essential?

pH is used in the science industry and housing. Some key uses of pH are as follows:

  • pH is used in the food preservation process, to make household cleaners, and in the baking method.
  • pH in toothpaste keeps our mouth’s pH normal. Otherwise, the bacteria in our mouth produce acid, which harms our teeth.
  • It is the key to leveling the pool’s pH and water purification.


pKa is a number that defines the acidity or basicity of any acid. We can say that pKa is the term that describes the strength of an acid.

If the pKa is lower, the acid is stronger and more able to donate the proton. Like pH, it is the negative base logarithm.

pKa = -log10Ka


Ka indicates the acid dissociation constant.

It helps measure the acid and how it completely dissociates in the solution. If the ka value is greater, the acid dissociates its ions to a greater extent. However, the pKa is lower.

What is the Relationship Between pKa and Ka?

The above equation shows the relationship between pKa and Ka. Hence, if the pKa is given, Ka’s value is easily measurable.

Ka = 10-pKa

For example, if we talk about hydrochloric acid having pKa -8 and acetic acid with pKa 4.75, but according to the pKa value, hydrochloric acid is stronger than acetic acid.

Relationship between pH and pKa
Relationship between pH and pKa

How to Calculate pKa?

pKa is a standard of the acidity of a combination and is specified as the negative logarithm (base 10) of the compound’s acid dissociation constant (Ka). The pKa value indicates the stability of an acid or base.

A lower pKa value implies a powerful acid, while an elevated pKa value indicates a weaker acid.

To calculate the pKa of a combination, you need to know the concentration of the acid and its conjugate base, and the Ka value. The Ka value can be received from a consideration book or empirical data.

The procedure for calculating pKa is as follows:

pKa = -log10(Ka)

Where Ka is the acid dissociation constant.

For example, if the Ka of acid is 1.8 x 10^-5, then the pKa can be calculated as observes:

pKa = -log10(1.8 x 10^-5)

pKa = 4.74

Therefore, the pKa of the acid is 4.74.

Difference Between pH and pKa

It determines the nature of the system, if it’s acidic or alkaline.It indicates the nature of an acid, whether it is strong or weak.
It represents the concentration of hydrogen ion present in the system or solution.It denotes the dissociation of an acid in aqueous solution.
It is the logarithmic evaluation opposite hydrogen ion concentration.It is the negative evaluation of logarithm Ka.
The pH indicates the degree of acidity or basicity of a solution.While the pKa is an indicator of the strength of an acid.
The pH can be measured directly using a pH meter, while pKa is usually determined through titration experiments.The concentration of an acid is varied until the pH of the solution or explanation is equal to the pKa of the acid.
pH vs. pKa

Mathematical Abbreviation of pH

The contraction “pH” stands for “potential of hydrogen.” It is a measure of the edge or alkalinity of an explanation and is specified as the negative logarithm of the attention of hydrogen ions (H+) in the explanation.

The mathematical procedure for pH is as follows:

pH = -log[H+]

Where [H+] is the awareness of hydrogen ions in moles per liter.

The pKa of an acid is the significance of its acidity. It is characterized as the negative logarithm of the acid dissociation constant (Ka). The procedure for calculating pKa is as follows:

pKa = -log (Ka)

Where Ka is the acid dissociation constant.

The discrepancy between pH and pKa is that pH is a criterion of the awareness of hydrogen ions in a solution, while pKa is a criterion of the strength of an acid.

Here is a table showing the connection between pH, pKa, and the ionization condition of an acid.

pHpKa Ionization State
< pKa > pKa Mostly undissociated
= pKa = pKa Half dissociated
> pKa< pKa Mostly dissociated
The ionization state of an acid
Let’s learn more about pH and pKa.

What is pH?

pH is a measure of the acidity or alkalinity of a solution, with a range of 0 to 14. A pH of 7 is Aqua evaluated as impartial, while importance below 7 implies acidity, and importance above 7 indicates alkalinity.

What is pKa?

pKa is a measure or quantity of the acidity of a molecule, specifically its ability to donate a proton (H+). It is the negative logarithm of a molecule’s acid dissociation constant (Ka), with lower pKa values indicating more potent acids.

What is the Connection Between pH and pKa?

pH and pKa are related through the Henderson-Hasselbalch equation, which describes the ratio of the concentrations and attentiveness of the protonated and deprotonated forms of acid to ipKa and the pH of the solution.

The equation is pH = pKa + log([A-]/[HA]), where [A-] is the attention of the deprotonated structure and [HA] is the attention of the protonated structure.

How Does the pH of a Solution Affect the Ionization State of Weak Acids and Bases?

The pH of a solution affects the ionization state of weak acids and bases by altering the ratio of their protonated and deprotonated forms.

When the pH is lower than the pKa of an acid, the protonated form predominates, while at higher pH values, the deprotonated form becomes more prevalent. The contrast is valid for weak bases.

What is the Significance of pKa in the Development of Medicines?

pKa is an important property in medicine development as it affects the solubility, stability, and absorption of a medicine or compound.

A medicine with a pKa value close to the physiological pH of the target tissue may be better absorbed and more effective. Additionally, modifying the pKa of a molecule can help to optimize its pharmaceutical properties.


  • In conclusion, pH is a standard of the acidity or alkalinity of an explanation, while pKa is a criterion of the stability of an acid.
  • The calculation of pKa involves the acid dissociation constant.
  • While the analysis of pH involves the concentration of hydrogen ions.
  • The association between pH and pKa can be used to predict the ionization state of an acid in a solution.

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