1.12 - Acids, Bases and Buffers

• What is a Bronsted-Lowry acid?

  A substance that can donate a proton
• What is a Bronsted-Lowry base?

  A substance that can accept a proton
• What happens when HCl reacts with water?

  It forms H3O+ and Cl- ions
• What is the relationship between an acid and its conjugate base?

  Each acid is linked to a conjugate base
• How is pH calculated?

  pH = - log [H+]
• What does the concentration of hydrogen ions indicate in strong acids?

  It equals the concentration of the acid
• What is the pH of a 0.1 mol dm-3 HCl solution?

  pH = 1.00
• How do you find [H+] from pH?

  [H+] = 1 x 10^-pH
• What is the concentration of HCl with a pH of 1.35?

  [H+] = 0.045 mol dm-3
• What equilibrium occurs in pure water?

  H2O ⇌ H+ + OH-
• What is the ionic product for water (Kw)?

  Kw = [H+][OH-]
• What is the value of Kw at 25°C?

  1 x 10^-14 mol² dm^-6
• How can you find [H+] if you know [OH-]?

  [H+] = Kw / [OH-]
• Why is pure water neutral?

  [H+] = [OH-]
• What is the pH of pure water at 25°C?

  pH = 7
• How does temperature affect the pH of pure water?

  Higher temperature lowers pH
• What is the pH of water at 50°C with Kw = 5.476 x 10^-14?

  pH = 6.6
• How do you calculate the pH of a strong base?

  Find [H+] using Kw expression
• What is the dissociation equation for NaOH?

  NaOH → Na+ + OH-
• What is the pH of a 0.1 mol dm-3 NaOH solution?

  pH = 13.00
• How do weak acids behave in water?

  They slightly dissociate, forming an equilibrium
• What is the dissociation expression for weak acids?

  Ka = [H+][A-]/[HA]
• What is the Ka for ethanoic acid?

  1.7 x 10^-5 mol dm-3
• What assumptions simplify the Ka expression for weak acids?

  [H+]eqm = [A-]eqm and [HA]eqm = [HA]initial
• How do you calculate the pH of a 0.01 mol dm-3 ethanoic acid?

  pH = 3.38
• What is the concentration of propanoic acid with a pH of 3.52?

  [CH3CH2CO2H] = 6.75 x 10^-3 mol dm-3
• What is the relationship between Ka and pKa?

  pKa = -log Ka
• How do you calculate pH in neutralization reactions?

  Determine moles of acid and base
• What is the first step in strong acid and strong base neutralization?

  Calculate moles of original acid
• How do you find the new concentration of excess H+ ions?

  [H+] = moles excess H+ / total volume
• What is the pH if excess acid is present?

  pH = - log [H+]
• How do you calculate pH if excess alkali is present?

  Use Kw to find [H+]
• What is the pH of a mixture of 45cm3 of 1.0 mol dm-3 HCl and 30cm3 of 0.65 mol dm-3 NaOH?

  pH = 0.47
• What is the pH of a mixture of 15cm3 of 0.5 mol dm-3 HCl and 35cm3 of 0.55 mol dm-3 NaOH?

  pH = 13.37
• How do you calculate the pH of a mixture involving strong diprotic acids?

  Consider moles of H+ produced
• What is the pH of a mixture of 15cm3 of 0.5 mol dm-3 HCl and 35cm3 of 0.45 mol dm-3 Ba(OH)2?

  pH = 13.68
• What is the pH of a mixture of 35cm3 of 0.5 mol dm-3 H2SO4 and 30cm3 of 0.55 mol dm-3 NaOH?


  pH = 0.55
• What is the significance of pKa values?

  pKa indicates the strength of an acid
• What is the formula for calculating pKa?

  pKa = -log Ka
• What is the formula for calculating pH?

  pH = -log[H+]