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Autoionization of water

Chemistry • Acid–Base Concepts • Knowledge-Based • 5 questions

Autoionization of water Knowledge-Based Download PDF

Chemistry · Acids & Bases · Chemistry · Acid–Base Concepts

5 Chemistry practice questions on Autoionization of water. Questions that assess core concepts and understanding.

Questions

  1. 1.

    Which of the following conditions must be satisfied for an aqueous solution to be classified as neutral at any given temperature?

    • A) [H3O+]=[OH−][\text{H}_3\text{O}^+] = [\text{OH}^-]
    • B) pH=7.00\text{pH} = 7.00
    • C) [H3O+]=1.0×10−7 M[\text{H}_3\text{O}^+] = 1.0 \times 10^{-7}\text{ M}
    • D) pH+pOH=14.00\text{pH} + \text{pOH} = 14.00
  2. 2.

    Why is the concentration of liquid water omitted from the equilibrium expression for the ion-product constant of water, KwK_w?

    • A) Water molecules do not participate as reactants in the proton-transfer process.
    • B) Water is a pure liquid solvent whose concentration remains essentially constant.
    • C) Liquid water dissociates completely into ions in dilute aqueous solutions.
    • D) The thermodynamic activity of a pure liquid solvent is defined as zero.
  3. 3.

    In the autoionization of liquid water, 2H2O(l)⇌H3O+(aq)+OH−(aq)2\text{H}_2\text{O}(l) \rightleftharpoons \text{H}_3\text{O}^+(aq) + \text{OH}^-(aq), which statement correctly describes the behavior of the reacting water molecules according to the Brønsted–Lowry definition?

    • A) Both water molecules act as Brønsted–Lowry acids by dissociating into free hydrogen ions and oxide ions.
    • B) One water molecule acts as an acid by donating a proton, while the other acts as a base by accepting the proton.
    • C) One water molecule acts as a Lewis acid by accepting an electron pair without any proton transfer taking place.
    • D) Both water molecules act as Brønsted–Lowry bases by capturing hydroxide ions directly from the surrounding solvent.
  4. 4.

    At 25 °C, an aqueous solution has a hydronium ion concentration of 2.0×10−5 M2.0 \times 10^{-5}\text{ M}. What is the concentration of hydroxide ions, [OH−][\text{OH}^-], in this solution?

    • A) 5.0×10−9 M5.0 \times 10^{-9}\text{ M}
    • B) 5.0×10−10 M5.0 \times 10^{-10}\text{ M}
    • C) 2.0×10−9 M2.0 \times 10^{-9}\text{ M}
    • D) 5.0×10−11 M5.0 \times 10^{-11}\text{ M}
  5. 5.

    Given that the autoionization of water is an endothermic process, how are the ion-product constant (KwK_w) and the pH of pure water affected when the temperature is raised from 25 °C to 60 °C?

    • A) KwK_w decreases and pH increases above 7.00, causing the water to become basic.
    • B) KwK_w increases and pH decreases below 7.00, while the water remains neutral.
    • C) KwK_w increases and the water becomes acidic because [H3O+][\text{H}_3\text{O}^+] exceeds [OH−][\text{OH}^-].
    • D) KwK_w remains constant at 1.0×10−141.0 \times 10^{-14} and pH stays at 7.00 because pure water is always neutral.