Chem chapter 1

• Pure substances have specific melting or boiling point under fixed conditions
• Rf value is Distance travelled by substance / distance travelled by solvent

  Rf number cannot be more than 1

  • Bigger Rf is more soluble
• Applications of fractional distillation

  Oil refineries seperate different substances from crude oil, like petrol or kerosene.

  Ethanol produced by glucose fermentation is extracted in breweries.
• locating agents sprayed on a colourless solution / chromatography results to produce coloured spots
• Time (s), Temp (K), Length (m), mass (kg), volume (m3)
• For time.

  Digital stopwatch - hundredth of a second

  Analogue stopwatch - tenth of a second
• For temp

  temp in K = temp in C +273

  
  

  Analogue thermometers - alcohol and mercury

  Digital thermometers - much wider range
• For length

  1m = 10 decimetre = 100cm = 1000mm
• For mass

  1kg = 1000g = 1 000 000 mg

  1t = 1000kg = 1 000 000g

  1kt = 1000t = 1 000 000kg
• Volume measurements

  1m3 = 1000 decimetre3 = 1 000 000 cm3
• Volum apparatus

  Pipette - fixed volume, e.g 10.0

  Flask - larger fixed volume

  Cylinder - range of volumes to the nearest 0.5cm3

  Burette - range of volumes to the nearest 0.05cm3
• solubility - How easily gas/solid dissolves in water
• density - How dense a gas is compared to the surrounding air
• relative molecular mass of air is 30
• Concentrated sulfuric acid is not for gases that react with sulfuric acid, but for most gases e.g. chlorine
• Quicklime (calcium oxide) for e.g. ammonia. Must be freshly heated. Not for gases which react with calcium oxide.
• Fused calcium chloride for e.g. hydrogen. Must be freshly heated. Not for gases which react to calcium chloride
• seperating solid-solid mixtures

  magnetic attraction, sieving, using suitable solvents, sublimation
• Seperating solid-liquid mixtures

  Filtration, evaporation to dryness, crystallisation, simple distillation
• Separating liquid-liquid mixtures

  Separating funnel, chromatography, fractional distillation
• Magnetic attraction

  To seperate magnetic solids (iron, nickel, cobalt) from non magnetic solids

  Used in recycling plants
• Sieving

  Used to separate solids with different particle sizes

  Used in bakery for flour
• Using suitable solvents

  Used to separate solid-solid mixtures where only one of the solids is soluble in solvent
• Sublimation


  To separate a substance that changes from solid to gaseous state directly

  • The solid sublimes into a gas upon heating and moves away from mixture. The gas will change back to solid on a cool surface. This deposit is called the sublimate.
• Filtration

  To separate insoluble solids from liquids.

  The liquid is called filtrate. The solid left is called residue.
• Evaporation to dryness

  To separate a dissolved solid from its solvent by heating until all the solvent has vaporised

  e.g. salt mixture
• Crystallisation

  Obtain a pure solid from its saturated solution. A saturated solution is one which no more solute can be dissolved.

  • heat solution until its saturated
  • cool solution until crystal form
  • pour mixture through a funnel to collect crystal as residue
• Simple distillation

  To separate a pure solvent from a solution.

  • in the condenser, water in at the bottom and water out at the top
  • boiling chip to ensure smooth boiling
  • pure water collected is the distillate
• Miscible liquids

  Form a uniform (homogeneous) solution when mixed together.
• Heterogeneous liquids

  Contain immiscible liquids

  E.g. water and oil.
• Phases

  When a heterogeneous mixture of 2 or more immiscible liquids are undisturbed, they separate into layers known as phases. Denset liquid at the bottom
• Separating funnel

  To separate immiscible liquids, least dense liquid at the top
• Chromatography

  To separate a mixture which has different solubilities in a given solvent.

  Solvent front refers to the final position of solvent
• Applications of Rf value - identify unauthorised substances in urine. Separate components like DNA
• Fractional distillation

  To separate miscible liquids with different boiling points.
• Fractional distillation - the initial distillate collected will contain the substance with a lower boiling point. To avoid contaminating the distillate with the other substance, the flask must be removed once the temperature reaches above the boiling point of the initial distillate.
• Length of fractionating column determines its ability to separate substances. Liquids with similar boiling points will require a longer fractionating column for better separation