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Acids, bases and pH Knowledge-Based Practice

Biology · Chemistry of Life · Biology · Atoms, Water & Chemical Bonds

5 Biology practice questions on Acids, bases and pH. Questions that assess core concepts and understanding.

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Questions

  1. 1.

    Which statement correctly describes the self-ionization (autoionization) of pure water at 25 °C?

    • A) It produces equal concentrations of hydronium ions and hydroxide ions, each measuring 1.0×10−7 M1.0 \times 10^{-7}\text{ M}.
    • B) It produces a higher concentration of hydronium ions than hydroxide ions due to the polarity of the oxygen atom.
    • C) It results in complete dissociation into individual hydrogen and hydroxide ions with a concentration of 1.0×10−14 M1.0 \times 10^{-14}\text{ M} each.
    • D) It does not produce any ions because the polar covalent bonds in water molecules cannot spontaneously dissociate.
  2. 2.

    Which of the following statements correctly characterizes an acidic aqueous solution at 25 °C?

    • A) The concentration of hydroxide ions exceeds the concentration of hydrogen ions, resulting in a pH above 7.
    • B) The product of the hydrogen ion and hydroxide ion concentrations is significantly greater than 10−14 M210^{-14}\text{ M}^2.
    • C) The solution contains hydrogen ions but completely lacks hydroxide ions due to neutralization.
    • D) The concentration of hydrogen ions exceeds the concentration of hydroxide ions, resulting in a pH below 7.
  3. 3.

    Which of the following statements correctly describes the chemical behavior of a base when it is dissolved in pure water?

    • A) It reduces the concentration of free hydrogen ions in the solution, resulting in a higher concentration of hydroxide ions than hydrogen ions.
    • B) It donates hydrogen ions to surrounding water molecules, thereby decreasing the pH of the solution below 7.0.
    • C) It increases the concentration of both hydrogen ions and hydroxide ions simultaneously in equal proportions.
    • D) It completely halts the dissociation of water molecules, causing the concentrations of both hydrogen and hydroxide ions to fall to zero.
  4. 4.

    Which of the following best describes the primary mechanism by which a biological buffer stabilizes the pH of an aqueous solution?

    • A) It accelerates the dissociation of water molecules into equal amounts of hydronium and hydroxide ions.
    • B) It permanently precipitates dissolved mineral ions to lock the solution at an exact neutral pH of 7.0.
    • C) It acts as an enzymatic catalyst that speeds up the irreversible destruction of strong acidic molecules.
    • D) It minimizes changes in pH by accepting hydrogen ions when they are in excess and donating them when they are depleted.
  5. 5.

    If the pH of an aqueous solution decreases from 8 to 5, how does the concentration of hydrogen ions change?

    • A) It decreases by a factor of 3.
    • B) It decreases by a factor of 1,000.
    • C) It increases by a factor of 3.
    • D) It increases by a factor of 1,000.

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