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The pH value of a sample of multiple-distilled water is

June 1, 2025 by rawan239

The pH value of a sample of multiple-distilled water is

zero

14

very near to zero

very near to seven

This question was previously asked in

UPSC CDS-1 – 2017

Download PDF Attempt Online

The correct answer is D) very near to seven.

pH is a measure of the acidity or alkalinity of a solution. Pure water is neutral because the concentration of hydrogen ions (H⁺) equals the concentration of hydroxide ions (OH⁻) produced by the auto-ionization of water (H₂O ⇌ H⁺ + OH⁻). At standard temperature (25°C), in pure water, [H⁺] = 10⁻⁷ mol/L. The pH is defined as -log₁₀[H⁺]. Thus, the pH of pure water is -log₁₀(10⁻⁷) = 7. Multiple-distilled water is highly purified water with most impurities removed. While it’s difficult to achieve a perfect pH of 7 in practice (e.g., due to dissolved CO₂ from the air forming carbonic acid, making it slightly acidic, or dissolved substances from the container), the theoretical and practical pH of pure, neutral water is very close to 7.

A pH of zero indicates a highly acidic solution (e.g., 1M HCl). A pH of 14 indicates a highly alkaline solution (e.g., 1M NaOH). Values very near zero would indicate strong acidity, which is not characteristic of pure water. Values very near seven indicate neutrality, which is the property of pure water.

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