MCQ Detailed View

The pH scale is used to measure the acidity or alkalinity of a solution. It ranges from 0 to 14. Solutions with a pH less than 7 are considered acidic, solutions with a pH greater than 7 are basic or alkaline, and the solution with a pH equal to 7 is neutral.

A neutral pH means that the concentration of hydrogen ions [H+][H⁺][H+] is exactly equal to the concentration of hydroxide ions [OH−][OH⁻][OH−]. Pure water at room temperature (25°C) is the standard example of a neutral substance, because it naturally dissociates into equal amounts of hydrogen and hydroxide ions. This balance makes its pH exactly 7.

Acids, such as hydrochloric acid (HCl), increase the hydrogen ion concentration, making the pH lower than 7. Bases, such as sodium hydroxide (NaOH), increase hydroxide ion concentration, making the pH higher than 7. The pH scale is logarithmic, meaning each change by one unit represents a tenfold change in hydrogen ion concentration.

The concept of pH was introduced by Søren Sørensen in 1909 as a simple way to express hydrogen ion concentration. Today, pH measurement is an essential analytical chemistry method, widely used in laboratories, industry, and environmental studies to check water quality, soil balance, and chemical reactions.

Therefore, on the pH scale, the neutral point is exactly at 7, which represents neither acidic nor alkaline conditions but a perfect balance of hydrogen and hydroxide ions.