Adecrease of one unit in the ph scale above represents a tenfold increase in the hydrogen ion concentration of a solution. for example, a solution having a ph of 4 is 10 times more acidic than a solution with a ph of 5. if acid precipitation rain changes the ph of a pond from 7.5 to 6.5, the level of hydrogen ion has changed by a factor of

Answer is: 10.
pH₁ (pond) = 7,5. Pond is bacic.
pH₂ (pond) = 6,5. Pond is acidic.
c₁( H₃O⁺) = ? concentration of hydronium ion.
c₂ (H₃O⁺) = ?
pH = -log c(H₃O⁺) ⇒ c(H₃O⁺) = 10∧(-pH).
c₁(H₃O⁺) = 10⁻⁷·⁵ = 3,2·10⁻⁸ M(mol/dm³).
c₂(H₃O⁺) = 10⁻⁶·⁵ = 3,2·10⁻⁷ M(mol/dm³).
factor = c₂(H₃O⁺)/ c₁(H₃O⁺) = 3,2·10⁻⁷/3,2·10⁻⁸ = 10 (ten times greater concentration).

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