chap 1 experimental chemistry

• hydrogen gas is less dense than air, insoluble in water
• oxygen is denser than air, soluble in water
• carbon monoxide is less dense than air, insoluble in water
• carbon dioxide is denser than air, soluble in water
• what are 3 methods of collecting gases

  displacement of water, downward delivery, upward delivery
• gases that are insoluble in water should be collected using displacement of water
• gases that are soluble in water and denser than air should be collected by downward delivery
• gases that are soluble in water and less dense than air should be collected by upward delivery
• gases that can be dried using sulfuric acid are all but NH3
• gases that can be dried using quicklime is all but SO2, SO3, CO2
• gases that can be dried using fused calcium chloride are all but SO2, SO3, CO2
• To separate solid- solid mixtures, we can use a magnet, sublimation or dissolution
• a magnet can be used to attract magnetic substances to separate the non- magnetic and magnetic material
• sublimation: place the mixture in an evaporating dish covered with an inverted filter funnel. gently heat the mixture. the substance (eg. ammonium chloride) changes into gas directly on heating. the white fumes of ammonium chloride rise and reform on the cold funnel. the non-volatile sodium chloride remains in the evaporating dish

  
• dissolution is to separate soluble and insoluble solids by using a solvent that dissolves one of the solids, while the insoluble solid can be removed by filtration. then the filtrate can be evaporated to dryness or crytalised
• to separate solid- liquid mixtures, use filtration, evaporation to dryness, crystallisation or simple distillation
• filtration: the mixture is poured into the filter funnel lined with filter paper. the filter paper has tiny holes through which the particles of the liquid are able to pass through but the particles of the solid are large so they cannot pass through the holes and will be trapped by the filter paper. the solid collected in the filter paper is the residue while the liquid passing through is called the filtrate
• evaporation to dryness is heating the solution until all the solvent has been evaporated but is only suitable for thermally stable substances
• crystallisation: solution is placed in an evaporating dish and heated to evaporate most of the solvent to make the solution saturated. the saturated solution will be then cooled, where crystals will form on cooling. crystals are then removed by filtering, washed with small amount of cold distilled water and dried by pressing them between sheets of filter paper
• how to test of solution is saturated: place a glass rod into the solution and remove. crystals would start to form on the surface of the glass rod
• solubilities of solids will increase as the temperature rises. when a saturated solution is cooled, the solubility of the solid will decrease and the excess solid will be crystallised out
• simple distillation: obtain pure liquid which is the solvent from a solution
• process of simple distillation:

  • solution is heated till it boil, where water evaporates and becomes steam
  • steam enters condenser and condenses back into water
  • water is hence, collected as distillate in the beaker
  • salt solution which remains in the distillation flask becomes more concentrated and is residue
• ways to separate liquid- liquid mixtures: fractional distillation, separating funnel and chromatography