pH of pure water at 25°C, kw = 1 x 10^-14
Correct answer: B. 7
- A. 0
- B. 7
- C. 14
- D. None of the above
Explanation
The pH of pure water at 25°C is 7 because water is neutral at this temperature, meaning it has equal concentrations of hydrogen ions (H+) and hydroxide ions (OH-). The ion-product constant for water (Kw) at 25°C is 1 × 10-14, which is the product of the concentrations of H+ and OH-. Mathematically, this means [H+] = [OH-] = 1 × 10-7 M. The pH is calculated as the negative logarithm of the hydrogen ion concentration: pH = -log[H+] = 7. Options A and C are incorrect because they represent extreme acidic and basic conditions, respectively, and Option D is incorrect because one of the listed values (7) is correct.
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About Acids, Bases and Salts
Acid and base behaviour is explained through the Bronsted-Lowry transfer of protons and the Lewis donation or acceptance of electron pairs. The topic includes pH, pOH, ionisation and water equilibrium, plus salt formation and hydrolysis, where a salt solution may become acidic, basic or neutral.
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