Chemistry · 10-12

Acids, Bases, and Salts: pH and Indicators

Acids and bases are fundamental categories of compounds defined by their ability to donate or accept protons. The pH scale measures acidity and basici

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What is the relationship between pH and pOH?

At 25°C, pH + pOH = 14. Since pH = -log[H+] and pOH = -log[OH-], and [H+] × [OH-] = 10^-14, we get this relationship. A neutral solution has pH = pOH = 7.

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Why do some indicators work better for certain pH ranges?

Indicators change color over a specific pH range (transition range, typically 1-2 pH units). An indicator's color change occurs when pH equals its dissociation constant (pKa). Choosing the right indicator depends on the expected pH of the solution.

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Can a salt solution ever have a pH of exactly 7?

Yes, but only certain salts produce pH 7. Salts of strong acids and strong bases (like NaCl) have pH 7 because neither the cation nor anion hydrolyzes. Salts of weak acids with strong bases or weak bases with strong acids will have pH above or below 7.

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