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Acids and Bases



Acids and bases are substances seen in many chemical reactions. An acid is a compound that can donate a proton to another compound, and a base is a compound that can accept a proton. Water is amphiprotic, acting as both an acid and a base, because it can accept and donate protons. The product of the concentration of [H3O+] and [OH] is always 1.0×10141.0\times10^{-14}, based on the fact that the concentration of each ion in water at 25℃ is 1.0×107{1.0\times10^{-7}}. The techniques of gravimetric and titration analysis can be used to determine the concentration of one of these ions in a solution of unknown concentration, or strength. The strength of an acid or a base is related to the proportion of the original substance that has dissociated (a liquid split into its ions) at equilibrium (when the acid and the base are at concentrations that neutralize each other). The ionization constant of a given acid or base is a ratio of the concentration of dissociated ions to undissociated acid or base and can be used to determine the concentration of ions. Once [H3O+] or [OH] is known, the pH or pOH can be determined by taking the inverse log of the concentration. For any solution, pH+pOH=14\rm{pH}+\rm{pOH}=14.

At A Glance

  • In the Brønsted-Lowry model, acids are compounds that lose a proton in solution, and bases are compounds that accept a proton in solution.
  • The ion product constant of water, Kw, is an equilibrium constant derived from the concentrations of H3O+ and OH present at equilibrium.
  • Gravimetric analysis uses the mass of a solid product precipitated from a reaction that contains the ion of interest in order to calculate the initial concentration of that ion.
  • Titration analysis is a method of determining the concentration of a solution by neutralizing it with a measured amount of solution of known concentration.
  • The ionization constant is the ratio of concentration of products to reactants at equilibrium and can be used to calculate the strength, or measure of concentration, of an acid or base.
  • The molecular structure of an acid or base plays a role in determining its ionization potential (how likely it is to ionize in water) and therefore its strength.
  • A measure of the concentration of hydronium ions (H3O+) in a solution is pH, and a measure of the concentration of hydroxide ions is pOH. The pH scale ranges from 1 to 14, with 1 being most acidic and 14 being most basic.