pH

Key Questions

  • Question #58475

    pH is a measure of hydrogen ion concentration. The pH scale was originated by Sorensen. He set 0 pH as the hydrogen ion concentration of a 1.0 molar solution of a strong monoprotic acid (like HCl). 14 on the pH scale uses its standard as the hydrogen ion concentration in a 1.0 molar concentration of a strong base (like NaOH). pH is actually a negative logarithmic scale. To determine pH, take the negative logarithm of the hydrogen ion concentration.

    Kathryn Celestine · 2 · Jul 1 2014
  • How does pH affect solubility?

    Answer:

    Decreasing the pH increases the solubility of sparingly soluble bases and basic salts.

    Explanation:

    Increasing the pH has the opposite effect.

    Many sparingly soluble compounds have solubilities that depend on pH.

    It all involves the application of Le Châtelier's Principle.

    Here are two common examples.

    Bases

    Zn(OH)2 is a sparingly soluble base.

    Zn(OH)2(s)⇌Zn2+(aq)+2OH-(aq)

    If you increase the pH by adding OH- ions, Le Châtelier's Principle says that the position of equilibrium will move to the left.

    The solubility of the Zn(OH)2 decreases.

    If you decrease the pH by adding H3O+ ions, the added H3O+ ions will react with the OH- ions and form water.

    OH- ions are removed from solution.

    According to Le Châtelier's Principle, the position of equilibrium moves to the right to replace the OH- ions.

    The solubility of the Zn(OH)2 increases.

    Salts of Strong Bases and Weak Acids

    CaCO3 is the sparingly soluble salt of the strong base Ca(OH)2 and the weak acid H2CO3.

    CaCO3(s)⇌Ca2+(aq)+CO2-3(aq)

    CO2-3 is a base.

    CO2-3(aq)+H2O(l)⇌HCO-3(aq)+OH-(aq)

    The overall equilibrium is

    CaCO3(s)+H2O(l)⇌Ca2+(aq)+HCO-3(aq)+OH-(aq)

    If you increase the pH by adding OH- ions, Le Châtelier's Principle says that the position of equilibrium will move to the left.

    The solubility of the CaCO3 decreases.

    If you decrease the pH by adding H3O+ ions, the added H3O+ ions will react with the OH- ions and form water.

    OH- ions are removed from solution.

    According to Le Châtelier's Principle, the position of equilibrium moves to the right to replace the OH- ions.

    The solubility of the CaCO3 increases.

    Here's a video that discusses the effect of pH on solubility.

    Ernest Z. · 42 · Jul 19 2014

Questions

Acids and Bases