acid, bases and salts

• Neutralisation reactions:

  • Metals general formula: metal + acid --> salt + hydrogen (where salt is an ionic compound)
  • Bases general formula: Acid + base --> salt and water
  • carbonates general formula: carbonate + acid --> CO2 + H2O + salt
• Salts from neutralisation reactions:

  • Hydrochloric acid (HCl) produces Chloride salts
  • Sulfuric acid (H2SO4) produces Sulfate salts (SO4)
  • Nitric acid (HNO3) produces Nitrate salts (NO3)
  • Phosphoric acid (H3PO4) produces Phosphate salts (PO4)
• Rules:

  • Acids have a pH less than 7
  • The more acidic a solution is, the lower the pH
  • Neutral substances like pure water have a pH of 7
  • Alkalis have a pH greater than 7
• Testing for acids and bases:

  • Litmus paper test:
  • Acid turns litmus paper red
  • Base turns litmus paper blue
• Importance of controlling soil acidity:

  • Plant growth is affected by soil acidity or alkalinity
  • Liming is used to treat acidic soil
  • Adding manure or compost helps with alkaline soil
• Method B for salt preparation by titration:

  • Stage 1: Acid in the burette, known volume of alkali in conical flask with indicator
  • Stage 2: Acid added until indicator changes color, repeat without indicator
  • Stage 3: Evaporate salt solution to form crystals
• Test for carbonate: add dilute acid -> bubbles produced
• Test for Chloride: acidify with nitric acid, add aqueous silver nitrate -> white precipitate
• ammonium -> ammonia produced on warming when reacted with sodium hydroxide
• Test for Nitrate: add aqueous sodium hydroxide, then aluminum foil, warm -> ammonia produced
• calcium -> produces white ppt which is insoluble in excess when reacted with sodium hydroxide. 


  -> produces no ppt or very slight white ppt when reacted with aqueous ammonia
• Test for ammonia gas: turns damp, red litmus paper turns blue (weak base)
• Test for carbon dioxide: turns limewater milky
• Test for chlorine: bleaches damp litmus paper
• Test for hydrogen: pops with a lit splint
• Test for oxygen: relights a glowing splint
• Copper (II) -> when reacted with sodium hydroxide, light blue ppt. Insoluble in excess when. 


  -> when reacted with aqueous ammonia, light blue ppt produced. Soluble in excess. Gives a dark blue solution.
• All nitrates are soluble in water
• All halides are soluble in water except silver and lead
• All sulfates are soluble in water except lead, barium and calcium
• All carbonates are insoluble in water except sodium, potassium and ammonium
• Iron (II) -> When reacted with both sodium hydroxide and aqueous ammonia, it forms a green ppt. It is insoluble in excess
• Iron (III) -> red brown ppt and insoluble in excess when reacted with both sodium hydroxide and ammonia
• Zinc -> White ppt, soluble in excess, forms colourless solution when reacted with sodium hydroxide and ammonia
• Lithium's flame colour is red
• Sodium's flame colour is yellow
• Potassium's flame colour is lilac
• Copper (II)'s flame colour is blue-green