What is pH Formula?

pH is a scale used in chemistry to describe the acidity or basicity of an aqueous solution. Acidic solutions (those containing a larger concentration of H+ ions) have a lower pH than basic or alkaline solutions.

The activity of the H+ ion in the solution accounts for the value. The negative logarithm of the molar hydronium-ion concentration is defined as pH.

The pH equation is written as:

pH = -log[H3O+]

pH = -log[H+]

Here, we will study the pH value formula, and how pH value is calculated in detail. 

pH Formula Chemistry

The pH scale, which normally spans from 0 to 14 in water, is used to determine the pH of an aqueous solution. A pH of 7 is regarded as neutral. Acidity is defined as a pH of less than 7. A pH of more than 7 is classified as basic. High hydronium concentrations and low hydroxide concentrations characterize acidic solutions. Hydroxide concentrations are high in basic solutions, while hydronium concentrations are low.

pH Calculation Formula of Water

The amphipathic property of water to behave as a proton donor and acceptor facilitates the synthesis of hydronium ( H3O+ ) and hydroxide ions ( OH ) during self-ionization. Hydronium ions have the same concentration as hydroxide ions in pure water. The concentrations of both hydronium and hydroxide ions are 1.0107% at 25°C. The ion product of water, Kw, is the equilibrium condition for water's self-ionization. Given below is the pH calculation formula:

Kw = [H3O+][OH-] = 1.0 × 10-14

pKw = pH + pOH = 14 

Strong Acids and Strong Bases

Strong acids and strong bases in dilute aqueous solutions basically complete their ionisation. Self-ionization of water occurs only to a small amount in aqueous solutions of strong acids and strong bases. Water self-ionization is a minor source of hydronium and hydroxide ions since it occurs in such a small amount. Knowing this, we can state that the strong acid is the principal source of hydronium ions when calculating hydronium concentration in an aqueous solution of a strong acid. When calculating the concentration of hydroxide ions in an aqueous solution of a strong base, we can also argue that the strong base is the principal source of hydroxide ions

pH Value Equation

How pH value is calculated for weak acids and weak bases?

Weak acids only partially dissolve in aqueous solutions and attain equilibrium, hence the equilibrium equation for that acid in solution determines how much they dissociate:.

Ka = [H3O+]/[A-][HA]

[H3O+]  is the Hydronium Concentration

[A-]  is conjugate base concentration

[HA]  is the Weak Acid concentration

In aqueous solutions, weak bases also only partially dissolve and approach equilibrium. The equilibrium equation for a base in solution is then the partial dissociation equation for that base:

Kb = [OH-]/[B+][B]

[OH-] = Hydroxide Concentration

[B+] = Ion

[B] = Weak Base

Solved Example:

1. A solution is 0.055 M HBr. What is the pH of this solution?

Solution: Use the pH equation which is:  pH = −log[H3O+]  .

0.055 M HBr, HBr is a strong acid

[H3O+] = 5.5 X 10-2M

pH = -log(5.5 X 10-2) = 1.26


The pH of an aqueous solution indicates how acidic or basic it is. The concentration of hydrogen ions in the solution is used to calculate it. pH can be calculated through the pH equation. The pH scale ranges from 0 to 14, with 0 being neutral and 14 being acidic. A solution with a pH less than 7 is acidic, a solution with a pH more than 7 is basic, and a pH of 7 is neutral. The pH scale, which ranges from 0 to 14, determines how acidic or basic a thing is. The pH and organic acid content of foods are two important parameters that can influence not only the kind of organisms that survive storage but also their spoiling activity.

FAQs (Frequently Asked Questions)

1. What is Meant By The pH Calculation Formula?

Ans: The measure of hydrogen ion concentration used to determine the acidity or alkalinity of a solution is known as pH. The following is the equation for calculating the pH: -log[H+] = pH

2. How Do You Calculate pH and pOH?

Ans: Take the negative log of the hydronium ion concentration to compute the pH. Simply subtract the pH from 14 to get the pOH. Take the negative log of the hydroxide ion concentration to determine the pOH. Simply subtract pOH from 14 to get the pH.

3. What is an Acid's pH?

Ans: The pH of water is a measurement of how acidic or basic it is. The range is 0 to 14, with 7 being the neutral value. Acidity is indicated by a pH less than 7, while a pH greater than 7 indicates a base. pH is a measurement of the proportion of free hydrogen and hydroxyl ions in water.