Acids and Bases

• 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 acids and their conjugate bases?

  • Each acid is linked to a conjugate base
  • Conjugate base forms after the acid donates a proton
• What is the formula for calculating pH?

  pH = - log [H+]
• How do strong acids behave in solution?

  They completely dissociate in water
• 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
• Calculate [H+] for a solution with pH of 1.35.

  [H+] = 0.045 mol dm-3
• What is the ionic product for water (Kw)?

  • Kw = [H+(aq)][OH-(aq)]
  • At 25°C, Kw = 1 x 10^-14 mol² dm^-6
• Why is pure water neutral?

  [H+(aq)] = [OH-(aq)] in pure water
• How do you calculate [H+] in neutral water using Kw?

  [H+] = √Kw
• 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 due to more H+ ions
• Calculate the pH of water at 50°C with Kw = 5.476 x 10^-14.

  pH = 6.6
• How do strong bases behave in solution?

  They completely dissociate into ions
• How do you calculate the pH of a strong base?

  Use Kw to find [H+]
• Calculate the pH of 0.1 mol dm-3 NaOH.

  pH = 13.00
• What is the dissociation expression for weak acids?

  • HA + H2O ⇌ H3O+ + A-
  • Ka = [H+][A-] / [HA]
• What is the Ka for ethanoic acid?

  Ka = 1.7 x 10^-5 mol dm-3
• What does a larger Ka indicate?

  A stronger acid
• Write the dissociation equation for propanoic acid.

  CH3CH2CO2H ⇌ H+ + CH3CH2CO2-
• How do you calculate the pH of a weak acid?

  1. Use Ka expression
  2. Assume [H+] = [A-]
  3. Assume [HA] remains constant
• Calculate the pH of 0.01 mol dm-3 ethanoic acid.

  pH = 3.38
• Calculate the concentration of propanoic acid with pH 3.52.

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

  • pKa = -log Ka
  • Ka = 10^-pKa
• What are the steps to calculate pH in neutralization reactions?

  1. Calculate moles of acid and base
  2. Determine which is in excess
  3. Calculate new concentration of excess ions
  4. Use pH formula
• How do you calculate pH after strong acid and strong base neutralization?

  Use excess H+ concentration
• Calculate the pH of a mixture of 45 cm³ of 1.0 mol dm-3 HCl and 30 cm³ of 0.65 mol dm-3 NaOH.

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

  pH = 13.37
• Calculate the pH of a mixture of 15 cm³ of 0.5 mol dm-3 HCl and 35 cm³ of 0.45 mol dm-3 Ba(OH)2.

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

  pH = 0.55
• What is the formula for calculating pH?

  pH = -log [H+]
• What is the concentration of H+ ions in the mixture after reacting HCl and Ba(OH)2?

  [H+] = 2.08 x 10^-14
• How do you calculate the moles of HCl used in the reaction?

  Moles HCl = conc x vol = 0.5 x 0.015
• What is the excess moles of OH- after the reaction between HCl and Ba(OH)2?

  0.024 moles of OH-
• How do you calculate the concentration of OH- ions in the resulting mixture?

  [OH-] = moles excess OH- / total volume
• What is the pH of the resulting mixture after reacting H2SO4 with NaOH?

  pH = 0.55
• How do you calculate the moles of H2SO4 used in the reaction with NaOH?

  Moles H2SO4 = conc x vol = 0.5 x 0.035
• What is the concentration of H+ ions after the reaction between H2SO4 and NaOH?

  [H+] = 0.28 mol dm-3