Chem (T3U1-2)

• Rules:

  1. Most carbonates are insoluble in water except sodium, potassium and ammonium
  2. All ammonium, potassium and sodium salts are soluble in water
  3. All nitrates are soluble in water
  4. Most sulfates are soluble in water except barium, calcium and lead
  5. Most chlorides are soluble in water except lead and silver
• Basic oxides: formed when a metal element combines with oxygen and reacts with acids to form a salt and water.

  • ex: NaOH, KOH, Ca(OH)2
• Acidic oxides: formed when a non-metal combines with oxygen and reacts with bases to form a salt and water

  • when dissolved in water, they produce an acidic solution with low pH
  • ex: carbon dioxide, sulfur trioxide, silicone dioxide
• Amphotheric oxides: behaves as an acid and base

  • salt and water formed in both cases
  • ex: aluminium oxide, zinc oxide, copper oxide, lead oxide
• Neutral oxides: show neither basic or acidic properties and don't form salts when reacted with acids or bases

  • ex: nitrogen monoxide, carbon monoxide, dinitrogen oxide
• Acids are a type of solution containing H+ ions and determines its acidity

  • have pH values below 7
  • can neutralise a base, forming salt and water
  • H+ ions is what makes a solution acidic
  • ex: HCl
• Bases are a type of solution containing -OH ions which determines its alkalinity

  • have pH values above 7
  • water soluble
  • can neutralise an acid, forming salt and water
  • OH- ions is what makes the solution alkalai
  • ex: NaOH
• Acid + metal --> Salt + hydrogen
• Acid + bases --> Salt + water
• Acid + metal carbonate --> Salt + water + carbon dioxide
• Bases + alkalis and ammonium salts --> Salt + ammonia + water
• Litmus paper: red in acid, blue in base
• Methyl orange: red in acid, yellow in base
• Phenolphtalein: colorless in acid, pink in base
• Method A is heating, filtration, evaporation and crystalisation

  • used when starting substance is solid
  • not applicable to pure substances of metals less reactive than hydrogen (Cu, Hg, Ag, Au) or very reactive ones (K, Na, Ca)
  • can be applied to metals less reactive than hydrogen only if it's oxides (CuO, AgO, etc)
  • only used to metals from magnesium to tin
• Method B is titration and precipitation

  titration:

  • used when starting substance is a liquid
  • neutralisation is done in this process where a phenolphtalein is used

  precipitation:

  • used to prepare insoluble salts
• Acidic reactions:

  1. Mg + H2SO4 --> MgSO4 + H2
  2. MgO + HCl --> MgCl2 + H2O
  3. CuCO3 + HCl --> CuCl2 + CO2 +H2O
• Alkaline reaction:

  1.

  • Mg(OH)2 + HCl --> MgCl2 + H2O
  • MgO + H2SO4 --> MgSO4 + H2O

  2. NH4Cl + NaOH --> NaCl + H2O + NH3
• Precipitation steps:

  1. dissolve soluble salts in water and mix with a stirring rod in a beaker
  2. filter it to remove precipitate from mixture
  3. wash filtrate to remove traces of other solutions
  4. leave in an oven to dry
• Titration steps:

  1. Add alkalai + indicator to conical flask with pipette
  2. Add acid to burette, noting the starting volume
  3. Slowly add acid to alkalai until indicator changes colour. Calculate volume of acid added, repeat steps 1-3 without indicator
  4. Transfer solution to evaporating basin. heat to partially evaporate water
  5. Remove evaporating basin from heat and allow filtrate to dry and crystalise
• Method A steps:

  1. heat acid until warm and add metal, base or carbonate, stirring constantly until it stops disappearing
  2. filter mixture to remove excess base and transfer solution to evaporating basin
  3. evaporate water from solution with bunsen burner until crystals appear
  4. remove evaporating basin from heat and allow filtrate to dry and crystalise