Acid and base

• Acid


  Proton donor (H+ ion donor)
• Acids


  • HCl(aq)
  • H2SO4(aq.)
• Acid


  • It turns damp blue litmus paper into red
  • It changes methyl orange into red
  • It changes thimolphthalein into colourless
• pH Scale


  Measures the acidity or the alkalinity (basicity) of any aqueous solution
• pH Scale


  • Strongly acidic
  • Weakly acidic
  • Neutral
  • Weakly alkaline
  • Strongly alkaline
• Acidic solution has a pH less than 7
• Alkaline solution has a pH more than 7
• Neutral solution has a pH equal 7
• Types of acids

  • Strong acids: completely dissociated in water giving great no. of H+ ions (protons)
  • Weak acids: Partially dissociated in water giving small no. of H+ ions (protons)
• Concentrated acid

  Has a little amount of water
• Diluted acid

  Has high amount of water
• Base

  Proton acceptor (H+ ion acceptor)
• Base

  • It turns damp red litmus paper into blue
  • It changes methyl orange into yellow
  • It changes thimolphthalein into blue
• Alkali


  A water soluble base as NaOH and KOH
• Reaction of alkali (base) with acid

  1. NH3 + HCl → NH4+ + Cl-

  2. NH3 + HNO3 → NH4+ + NO3-

  3. NH3 + H2O ⇌ NH4+ + OH-

  4. N2H4 + H2O ⇌ N2H5+ + OH-
• Types of bases

  • Strong bases (alkalis): completely dissociated in water giving great no. of OH- ions
  • Weak bases: partially dissociated in water giving small no. of OH- ions
• Strong base reaction


  NaOH + H2O → Na+ + OH-(aq)
• Test for strong and weak acids/bases

  • Use pH paper: strong acid (pH 0-3), weak acid (pH 4-6), strong base (pH 12-14), weak base (pH 8-11)
  • Add universal indicator: strong acid (red), weak acid (orange/yellow), strong base (violet), weak base (blue)
• Acid - lose proton, Base - gain proton
• Neutralization reaction


  Reaction between acid (H+) and base (OH-) to form water
• Neutralization reaction

  H+ (aq) + OH-(aq) → H2O (l)
• Indicator


  Substance that changes colour in acidic vs alkaline medium
• Indicators

  • Phenolphthalein
  • Thimolphthalein
  • Methyl orange
• Universal indicator is not suitable for acid-base titration because it has a range of colour changes
• Adding excess acid HCl


  pH changes from 13 to 2
• Comparing concentration of two solutions

  • If the concentrated solution is in the flask, it takes more volume
  • If the concentrated solution is in the burette, it gives less volume