equilibria

• Conjugate acids and bases are pairs where an acid and a base differ by one proton, like NH3 and NH4+, or HF and F–
• Calculating pH or H+ concentration:

  • pH = -log10[H+]
  • [H+] = 10^-pH
• For the equation HA ⇋ H+ + A-, Ka is the acid dissociation constant, with lower values indicating the equilibrium lies further left
• pKa = -log10(Ka) for weak acids; as pKa increases, the acid strength decreases
• Kw = [H+][OH-], with a value of 1.00 x 10^-14 mol^2 dm^-6 at room temperature
• Steps to calculate the pH of a strong base:

  1. Calculate the concentration of hydroxide ions

  2. Calculate the concentration of H+ ions using Kw

  3. Convert [H+] into pH: pH = -log10[H+]
• For strong acids, pH is easily calculated as [H+] = [HA], so pH = -log10[H+]
• An acidic buffer has a pH less than 7 and contains a large amount of weak acid and its conjugate base, minimizing pH changes when acid or alkali is added
• Buffers in the blood, like HCO3- ions, help maintain blood pH between 7.35 and 7.45 by shifting equilibrium to adjust hydrogen ion concentrations
• Buffers can be used to check and adjust pH meter readings by inserting a pH probe into a buffer solution with a known pH
• For weak acids in buffer calculations:

  • [H+] ≠ [A-] as the buffer has a larger concentration of A-
  • [HA] at equilibrium = [HA] at the start due to the added A- ions pushing the equilibrium to the left
• The solubility constant indicates how much a compound dissociates in water and only applies to saturated compounds
• The equilibrium constant for solubility is called the solubility product (Ksp) and is calculated by multiplying the concentrations of the ions in the equilibrium equation
• In the Ksp equation, solid compounds are not included because they are in a heterogeneous equilibrium
• The units for solubility products are calculated by multiplying the units of the concentrations involved in the Ksp equation
• The solubility product for a compound remains the same under the same conditions provided that the solution is saturated
• The common ion effect occurs when a sparingly soluble substance is less soluble in a solution containing ions it has in common
• In the common ion effect, the position of equilibrium shifts to counteract the increased concentration of ions in the solution
• Partition coefficients (Kpc) are used to determine the solubility of a substance in two immiscible liquids, with no units due to unit cancellation