acid and base

• What do acid-base equilibria involve?

  Transfer of protons between substances
• How are substances classified as acids or bases?

  Based on their interaction with protons
• What is a Brønsted-Lowry acid?

  A proton donor
• What is a Brønsted-Lowry base?

  A proton acceptor
• What does acid strength not refer to?

  Concentration of a solution
• How is a strong acid defined?

  Completely dissociates to ions in solution

  
• What is the pH range of a strong acid?

  pH 0-1
• How is a weak acid defined?

  Only slightly dissociates in solution

  
• What is the pH range of a weak acid?

  pH 3-5
• What are the pH ranges for strong and weak bases?

  Strong bases: pH 12-14; weak bases: pH 9-11

  
• What does pH measure?

  Acidity and alkalinity
• What type of scale is pH?

  A logarithmic scale from 0 to 14

  
• What does a pH of 0 indicate?

  An acidic solution with high H$^+$ concentration
• What does a pH of 14 indicate?

  A basic solution with low H$^+$ concentration
• How can the concentration of H$^+$ ions be determined?


  Using the pH value
• What is the ionic product of water?

  Water slightly dissociates to ions
• What is the value of Kw at 25°C?

  1 x 10$-14$
• How does temperature affect Kw?

  Kw changes as temperature changes
• What type of reaction is the forward reaction in the equilibrium of water?

  Endothermic reaction
• What happens to H$^+$ ions as temperature increases in water?


  More H$^+$ ions are produced
• How does increased temperature affect the acidity of water?

  Water becomes more acidic
• What do weak acids and bases do in solution?

  Only slightly dissociate to form equilibrium
• What is the equilibrium dissociation constant for weak acids?

  Ka

  
• How can pKa be found?

  Using the equilibrium constant Ka

  
• How can pH be determined for weak acids and bases?

  Using relationships of Ka, pKa, and [H$^+$]
• What methods are used to find pH in different scenarios?

  • HA in excess: Use [HA] and [A$^-$] with Ka
  • A$^-$ in excess: Use Kw to find [H$^+$]
  • HA = A$^-$: pKa equals pH
• What does a pH titration curve show?

  How pH changes during an acid-base reaction

  
• What is the neutralisation point in a titration curve?

  A large vertical section through the equivalence point
• How is a titration curve produced?

  By slowly adding alkali to an acid

  
• What happens to the accuracy of the titration curve with smaller added volumes?

  The curve becomes more accurate
• What is the neutralisation point for a strong acid-strong base reaction?

  pH 7
• What is the neutralisation point for a strong acid-weak base reaction?

  Less than pH 7 (more acidic)
• What is the neutralisation point for a weak acid-strong base reaction?

  Greater than pH 7 (more basic)
• What is the neutralisation point for a weak acid-weak base reaction?

  Normally pH 7 but hard to determine
• Why are specific indicators used in titrations?

  To indicate pH change within a certain range

  
• What are the two common indicators used at A-Level?

  • Methyl orange
  • Phenolphthalein

  
• What is the color change of methyl orange in acids?

  Orange in acids, yellow at neutralisation
• What is the color change of phenolphthalein in alkalis?

  Pink in alkalis, colorless at neutralisation
• Why is it important to select the correct indicator in a titration?

  To match the pH range of the reaction
• What is a buffer solution?

  • Contains a weak acid and its salt
  • Contains a weak base and its salt
  • Resists changes in pH when small volumes of acid or base are added