1.12 Acid & Bases

• buffer


  a solution that resists changes in pH when small volumes of acid or bases are added
• bronstead lowry acid

  proton donor, NH4+
• bronstead lowry base

  proton acceptor, OH-
• strong acid

  completely dissociates to ions in solution
• weak acid

  slightly dissociates in solution
• pH

  measure of acidity and alkalinity -- shows conc of H+ ions in solution
• to calulate pH of a strong base

  use Kw
• for Kw; effect of increasing temp

  favours the endo reaction - forward reaction, creating more H+ ions - solution more acidic
• to calculate pH of weak acid or base

  Ka
• pKa = -logKa
• Ka= 10^-pKa
• for weak acids 


  assume conc at equilibrium = original conc of acid
• half way neutralisation point

  assume [HA] = [A-], --> [H+] = Ka --> pH= pKa
• diluting acid or base

  [H+] = [H+]old * old vol / new vol
• adding acid to buffer

  fully dissociates into H+, increasing conc of H+ -- equilibrium shifts left, so ratio of [HA], [A-] stays almost constant -- pH stays constant
• adding base to buffer

  OH- reacts with H+ -> H2O -- conc of H+ decreases, so equilibrium shifts right to produce more H+. Ratio of [HA], [A-] stays roughly constant, so pH stays constant