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What is the concentration of H ⁺ ions in pure water at 25°C ?
1×10⁻⁵ M
1×10⁻¹ M
1×10⁻⁴ M
1×10⁻⁷ M
1×10⁻⁵ M
At 25 degrees Celsius, pure water undergoes self-ionization to a very small extent, resulting in equal concentrations of hydronium ions and hydroxide ions. The ionic product of water is 1 times 10 to the power of negative 14, meaning the concentration of H+ ions is 1 times 10 to the power of negative 7 M.
At 25 degrees Celsius, pure water undergoes self-ionization to a very small extent, resulting in equal concentrations of hydronium ions and hydroxide ions. The ionic product of water is 1 times 10 to the power of negative 14, meaning the concentration of H+ ions is 1 times 10 to the power of negative 7 M.
This concept forms the scientific foundation for the pH scale, developed by S.P.L. Sorensen in 1909, which is a fundamental metric in Environmental Chemistry and Biology sections of General Science in UPSC and SSC exams.
Pure water is neutral at 25 degrees Celsius with a pH of 7.
The product of H+ and OH- ion concentrations is always 10 to the power of negative 14 at 25 degrees Celsius.
As temperature increases, the self-ionization of water increases, affecting the pH value.
The pH is calculated as the negative logarithm of the hydrogen ion concentration.
A solution with a pH less than 7 is acidic, while a solution with a pH greater than 7 is basic or alkaline.
Option A (1x10⁻⁵ M) corresponds to an acidic solution with a pH of 5.
Option B (1x10⁻¹ M) corresponds to a highly acidic solution with a pH of 1.
Option C (1x10⁻⁴ M) corresponds to an acidic solution with a pH of 4.
D is correct — The concentration of H+ ions in pure water at 25 degrees Celsius is 1x10⁻⁷ M, resulting in a neutral pH of 7.
In competitive exams, relate this to 'Environmental Pollution' topics where the pH of rainwater is discussed; natural rainwater has a pH of about 5.6 due to dissolved carbon dioxide, making it slightly acidic.
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