pH Formula

pH Formula

pH is a measure of the acidity or basicity (alkalinity) of a solution. It quantifies the concentration of hydrogen ions (H⁺) present in the solution. The pH scale ranges from 0 to 14

In our daily lives, we use many of these acids. Vinegar or acetic acid in the kitchen for cooking purposes. pH Formula helps in identifying the pH value of a solution which means finidng strength of acidity or basicity of a given solution. Learn more about pH Formula and importance of pH in this post by Extramarks.

pH Meaning

The name “pH” stands for “potential of Hydrogen” or “power of Hydrogen,” indicating the concentration of hydrogen ions (H⁺) in the solution.

The pH scale is used to determine the acidity or basicity (alkalinity) of an aqueous solution.

• The pH scale spans from zero to fourteen.
• A pH of 7 is neutral, indicating that the concentration of H⁺ ions equals the concentration of hydroxide ions (OH⁻).
• A pH of less than 7 implies an acidic solution with a higher concentration of H⁺ ions than OH⁻.
• A pH above 7 implies a basic (alkaline) solution with a higher concentration of OH⁻ ions compared to H⁺.

pH Formula

pH Formula is used to give the pH of a solution. Soren Peter, a biochemist, coined the term pH for the first time in 1909. The formula for calculating pH is:

pH=−log₁₀​[H⁺]

where,

• [H+]: This represents the concentration of hydrogen ions in the solution, measured in moles per liter (M).
• log10​: This denotes the base 10 logarithm. The logarithm helps in converting the hydrogen ion concentration into a more manageable scale.
• Negative Sign: The negative sign ensures that higher concentrations of hydrogen ions (which correspond to more acidic solutions) result in lower pH values

Converting pH to Hydrogen Ion Concentration

The pH formula can be rearranged to find the hydrogen ion concentration if the pH is known:

[H⁺]=10^−pH

For example, if the pH of a solution is 5:

1. Apply the Inverse Formula: [H⁺]=10⁻⁵
2. Calculate the Concentration: [H+]=1×10⁻⁵M

pH Value Equation

The equation to calculate the pH of an aqueous solution in terms of hydronium ion concentration is:

pH=−log[H₃O⁺]

pOH: The following equation can be used to calculate an aqueous solution’s pOH, which is correlated with pH:

pOH=−log[OH^–]

Instead of the hydronium concentration, this equation uses the concentration of hydroxide in an aqueous solution.

Relationship Between pH, pOH, and pK_w

At 25°C, the relationship between pH, pOH, and

pKw​ is given by:

pH + pOH = pKw​

Since Kw​ is 1×10⁻¹⁴ at 25°C:

pKw​=−log_10​(1×10⁻¹⁴)=14

Therefore, at 25°C: pH+pOH=14

Importance of pH in Real Life

pH has significant impact in our daily life. The importance of pH and its application in daily life is mentioned below:

• Maintaining blood pH (usually around 7.4) is crucial for normal physiological function.
• pH levels influence the shelf life and safety of food goods. For example, acidic conditions (low pH) hinder bacterial development and are used to preserve goods such as pickles and jams.
• Soil pH influences nutrient availability and microbial activity, which in turn affects plant development and agricultural yield. Farmers frequently modify soil pH with lime (to boost pH) or sulfur (to drop pH).
• Maintaining the right pH in swimming pools (usually between 7.2 and 7.8) enables successful disinfection and swimmer comfort.
• Many chemical processes require precise pH regulation to provide optimal reaction conditions and product quality.
• pH is an important indication of water quality in rivers, lakes, and oceans.

Solved Examples using pH Formula

Example 1: Calculate the pH of a solution with a hydrogen ion concentration [H+] of

1×10⁻³ M.

Solution:

pH=−log₁₀​[H⁺]

pH=−log_10​(1×10⁻³)

pH=−(−3)

pH=3

Example 2: Calculate the pH of a solution with a hydroxide ion concentration [OH−] of 1×10⁻⁴ M.

Solution:

pOH = −log_10​[OH⁻]

pOH = −log_10​(1×10⁻⁴)

pOH = −(−4)

pOH = 4

pH+pOH = 14

pH + 4 = 14

pH = 14−4 = 10

Example 3: Calculate the pH of a solution with a hydrogen ion concentration [H+] of

3.2×10−5 M.

Solution:

pH = −log₁₀​[H⁺]

pH = −log₁₀​(3.2×10⁻⁵)

log_10​(3.2×10⁻⁵)=log_10​(3.2)+log_10​(10⁻⁵)

log_10​(3.2)≈0.505

log₁₀​(10⁻⁵)=−5

log₁₀​(3.2×10⁻⁵)=0.505−5=−4.495

pH=−(−4.495) = 4.495

It is necessary to solve examples based on pH Formula. Solving questions from time to time will help students in retaining the pH Formula for a longer period of time. Extramarks can help students in solving questions related to the pH Formula.