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Updated on 16th May, 2023 , 6 min read
In the world of chemistry, the pH formula plays a crucial role in determining the acidity or alkalinity of a substance. Whether you're a student, scientist, or simply curious about the science behind pH, this article will provide you with a comprehensive understanding of the pH formula and its significance in maintaining the delicate acid-base balance. Read on to unravel the mysteries of pH and its practical applications.
The pH scale, derived from the German word "Potenz" meaning "Power," is a logarithmic scale used to determine the acidity or alkalinity of a solution. It represents the "power of Hydrogen" and was initially introduced by Soren Sorensen, a Danish chemist.
The pH equation quantifies even minute quantities of H+ ions in a solution. It is defined as the negative logarithm to the base ten of the concentration of H+ or H3O+ in moles per liter.
The pH scale spans from 0 to 14 and serves as a classification system for solutions based on the following criteria:
The pH scale is logarithmic, meaning that each unit represents a tenfold difference in acidity or alkalinity. For example, a substance with a pH of 4 is ten times more acidic than a substance with a pH of 5. Similarly, a substance with a pH of 9 is ten times more alkaline than a substance with a pH of 8.
The pH scale is utilized in chemistry to express the acidity or alkalinity of a water-based solution. A solution is considered acidic when it contains a higher concentration of H+ ions, resulting in a lower pH compared to alkaline or basic solutions. The pH scale spans from 0 to 14, where a pH value between 0 and 6 indicates acidity, 7 represents neutrality, and a pH value between 8 and 14 signifies alkalinity. An acid, such as hydrochloric acid, serves as a prime example of an acidic substance, while calcium hydroxide exemplifies a base, and sodium chloride is an example of a salt.
The pH value is determined based on the activity of H+ ions within the solution. It is calculated by taking the negative logarithm of the molar concentration of hydronium ions ([H3O+]), which can also be represented as the concentration of H+ ions ([H+]). Thus, the pH equation is expressed as:
pH = -log[H3O+]
pH = -log[H+]
Given the pH value of a solution, it is possible to calculate the concentration of ions present in that solution. The pH equation can be rearranged as follows:
The concentration of H+ ions, [H+], can be determined as [H+] = 10^(-pH).
Similarly, there is another scale called the pOH scale, which is used to measure the concentration of ions in a solution. In the pOH scale, the negative logarithm of [OH-] is denoted as pOH:
pOH = -log [OH-].
The concentration of OH- ions, [OH-], can be calculated using the equation [OH-] = 10^(-pOH).
Pure water is considered neutral, indicating that it has a pH value of 7, which signifies its lack of acidity or basicity. When pure water undergoes auto-ionization of self-ionization, it does so to a negligible extent. The concentration of H+ ions in water is [H+] = 1.0 x 10^-7 moles per litre.
Consequently, the pH of water can be determined as follows:
pH = -log [1.0 x 10^-7]
pH = -(-7)
pH = 7
The process of self-ionization occurs in water, leading to its dissociation in the following manner:
Based on the Law of Mass Action, the Equilibrium Constant (Kw) can be expressed as Kw = [H3O+] [OH-]/[H2O]. Considering water as the solvent, its concentration can be estimated as 1.
Therefore, Kw = [H3O+] [OH-]. At room temperature, it is observed that Kw equals 1.0 x 10^-14.
From this, it can be inferred that in an aqueous solution:
The interrelationship between pOH, pH, and pKw can be explained as follows:
The negative logarithm of Kw is represented as pKw:
–log Kw = pKw
–log Kw = –log ([H3O+] [OH-])
–log Kw = (–log [H3O+]) + (–log [OH-])
Therefore, we can deduce that pKw = pH + pOH.
Given that Kw equals 1.0×10^-14, it follows that pKw is equal to 14.
Consequently, the equation pH + pOH = 14 holds true.
Weak acids undergo partial dissolution in an aqueous solution and establish an equilibrium state. The equilibrium equation for such acids can be represented as:
HA = H+ + A-
The equilibrium constant for the weak acid, Ka, is calculated as the product of the hydronium ion concentration ([H3O+]) and the conjugate base concentration ([A-]):
Ka = [H3O+][A-]
Here,
Similarly, when weak bases are present, they also partially dissolve and reach an equilibrium state. The equilibrium equation for such bases and their partial dissociation can be described as:
BOH = OH- + B+
The equilibrium constant for the weak base, Kb, is determined by the product of the hydroxide ion concentration ([OH-]) and the concentration of the ion formed ([B+]):
Kb = [OH-][B+]
In this context,
pH plays a vital role in various aspects of our daily lives, including:
To measure pH accurately, various methods and devices are available. The most common instrument used is the pH meter, which measures the electrical potential difference between a reference electrode and a pH-sensitive glass electrode. pH test strips and color-changing indicators are also widely used for quick and convenient pH testing.
Maintaining the correct pH balance is vital for many industrial processes and biological systems. Different substances are used to adjust pH levels:
pH paper serves as a tool to determine the pH level of a solution by immersing it in the solution and comparing the resulting color to a color chart to obtain the corresponding pH value.
The applications of pH include:
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By - Nikita Parmar 2023-08-25 09:48:44 , 11 min readThe pH formula is expressed as pH = -log[H3O+] or pH = -log[H+], where [H3O+] or [H+] represents the concentration of hydronium ions in an aqueous solution.
The pH formula calculates the negative logarithm of the hydronium ion concentration, providing a measure of the acidity or alkalinity of a solution.
The negative logarithm converts the concentration of hydronium ions into a logarithmic scale, making it easier to represent the wide range of acid and alkaline levels.
The pH scale ranges from 0 to 14, where 7 is considered neutral. Values below 7 indicate acidity, and values above 7 indicate alkalinity.
To calculate pH, you substitute the hydronium ion concentration into the pH formula and apply the negative logarithm function to obtain the pH value.
The pH formula is primarily applicable to aqueous solutions where the presence of water allows for the formation of hydronium ions. It may not be directly applicable to non-aqueous systems.
[H3O+] refers to the concentration of hydronium ions, which are formed when water molecules combine with hydrogen ions ([H+]).
Lower pH values indicate higher acidity, while higher pH values indicate greater alkalinity. pH serves as a measure of the balance between acid and base concentrations.
A pH value of 7 indicates neutrality, meaning the solution is neither acidic nor alkaline. It represents a balance between acid and base concentrations.
A pH value of 7 indicates neutrality, meaning the solution is neither acidic nor alkaline. It represents a balance between acid and base concentrations.
The pH formula finds extensive use in various fields, such as chemistry, biology, environmental science, and industry, for measuring and controlling the acidity or alkalinity of solutions. It helps ensure optimal conditions for chemical reactions, biological processes, and industrial processes.
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